Science

In Sickness and In Health
Purpose of Public Health
Public health is the science of protecting and improving the health of families and communities through promotion of healthy lifestyles, research for disease and injury prevention and detection and control of infectious diseases.
Overall, public health is concerned with protecting the health of entire populations. These populations can be as small as a local neighbourhood, or as big as an entire country or region of the world.
Public health professionals try to prevent problems from happening or recurring through implementing educational programs, recommending policies, administering services and conducting research – in contrast to clinical professionals like doctors and nurses, who focus primarily on treating individuals after they become sick or injured. Public health also works to limit health disparities. A large part of public health is promoting healthcare equity, quality and accessibility.
The focus of a public health intervention is to prevent and manage diseases, injuries and other health conditions through surveillance of cases and the promotion of healthy behaviors, communities and environments. Many diseases are preventable through simple, non-medical methods. For example, research has shown that the simple act of hand washing with soap can prevent many contagious diseases.[4] In other cases, treating a disease or controlling a pathogen can be vital to preventing its spread to others, such as during an outbreak of infectious disease, or contamination of food or water supplies. Public health communications programs, vaccination programs, and distribution of condomsare examples of common public health measures. Measures such as these have contributed greatly to the health of populations and increases in life expectancy.
Public health plays an important role in disease prevention efforts in both the developing world and in developed countries, through local health systems and non-governmental organizations. The World Health Organization (WHO) is the international agency that coordinates and acts on global public health issues. Most countries have their own government public health agencies, sometimes known as ministries of health, to respond to domestic health issues. For example, in the United States, the front line of public health initiatives are state and local health departments. The United States Public Health Service (PHS), led by the Surgeon General of the United States, and the Centers for Disease Control and Prevention, headquartered in Atlanta, are involved with several international health activities, in addition to their national duties. In Canada, the Public Health Agency of Canada is the national agency responsible for public health, emergency preparedness and response, and infectious and chronic disease control and prevention. ThePublic health system in India is managed by the Ministry of Health & Family Welfare of the government of India with state owned health care facilities.
Hospitals, Clinics and Other Health Providers
Hospital: It is a health care institution providing patient treatment with specialized staff and equipment. The best-known type of hospital is the general hospital, which has an emergency department. A district hospital typically is the major health care facility in its region, with large numbers of beds for intensive care and long-term care. Specialised hospitals include trauma centres, rehabilitation hospitals, children’s hospitals, seniors' (geriatric) hospitals, and hospitals for dealing with specific medical needs such as psychiatric problems (see psychiatric hospital) and certain disease categories. Specialised hospitals can help reduce health care costs compared to general hospitals.
A teaching hospital combines assistance to people with teaching to medical students and nurses. The medical facility smaller than a hospital is generally called a clinic. Hospitals have a range of departments (e.g., surgery, and urgent care) and specialist units such as cardiology. Some hospitals have outpatient departments and some have chronic treatment units. Common support units include pharmacy, pathology, and radiology.
Hospitals are usually funded by the public sector, by health organisations (for profit or nonprofits), by health insurance companies, or by charities, including direct charitable donations. Historically, hospitals were often founded and funded by religious orders or charitable individuals and leaders.
Today, hospitals are largely staffed by professional physicians, surgeons, and nurses, whereas in the past, this work was usually performed by the founding religious orders or by volunteers. However, there are various Catholic religious orders, such as the Alexia sand the Bon Secours Sisters that still focus on hospital ministry today, as well as several other Christian denominations, including the Methodists and Lutherans, which run hospitals. In accordance with the original meaning of the word, hospitals were originally "places of hospitality", and this meaning is still preserved in the names of some institutions such as the Royal Hospital Chelsea, established in 1681 as a retirement and nursing home for veteran soldiers.
The earliest known institutions aiming to provide cures were Ancient Egyptian Temples (which were devoted to the Greek Healer god named Asclepia).Institutions which were made Especially to cure the ill were found In India when Fa Xian, A buddhist Monk travelled across India. These institutions in India were based upon the works of Charaka (who was an ancient Teacher and Researcher for the Human body ) and his work known as the Charakasamhita.The Romans created Buildings called valetudinarian for the care of sick slaves, gladiators and Soldiers as back as 100 BC.
Clinics:  They are the healthcare facilities devoted to the care of outpatients (someone who needs treatment for a span less than 24 Hours.). The Word Clinic derives from the Greek word Klinein meaning to slope/lean/recline, which makes the literal meaning of Clinic to be, ‘one who receives baptism on a sick bed'.
The function of clinics differs from country to country. For instance, a local general practice run by a single general practitioner provides primary health care and is usually run as a for-profit business by the owner, whereas a government specialist clinic may provide subsidised specialised health care.
Some clinics function as a place for people with injuries or illnesses to come and be seen by a triage nurse or other health worker. In these clinics, the injury or illness may not be serious enough to warrant a visit to an emergency room, but the person can be transferred to one if required. Treatment at these clinics is often less expensive than it would be at a casualty department. Also, unlike an ER these clinics are often not open on a 24 x 7 x 365 basis. They sometimes have access to diagnostic equipment such as X-ray machines, especially if the clinic is part of a larger facility. Doctors at such clinics can often refer patients to specialists if the need arises.
Clinics are often associated with a general medical practice, run by one or several general practitioners or clinics are usually operated by physiotherapists and psychology clinics by clinical psychologists, and so on for each health profession. Some clinics are operated in-house by employers, government organizations or hospitals and some clinical services are outsourced to private corporations, specialising in provision of health services. In China, for example, owners of those clinics do not have formal medical education. There were 659,596 village clinics in China in 2011. Health care in India, China, Russia and Africa is provided to vast rural areas by mobile health clinics or roadside dispensaries, some of which integrate traditional health practices. In India these traditional clinics provide ayurvedic medicine and unaniherbal medical practice. In each of these countries traditional medicine tends to be a hereditary practice.
Medical Laboratories and/For Research: It is a laboratory where tests are done on biological specimens in order to get information about the health of a patient. Such laboratories may be divided into categorical departments such as microbiology, haematology, clinical biochemistry,immunology, serology, histology, cytology, cytogenetics, or virology. In many countries, there are two main types of labs that process the majority of medical specimens. Hospital laboratories are attached to a hospital, and perform tests on these patients. Private or community laboratories receive samples from general practitioners, insurance companies, and other health clinics for analysis.
A biomedical research facility is where basic research or applied research is conducted to aid the body of knowledge in the field of medicine. Medical research can be divided into two general categories: the evaluation of new treatments for both safety and efficacy in what are termed clinical trials, and all other research that contributes to the development of new treatments. The latter is termed preclinical research if its goal is specifically to elaborate knowledge for the development of new therapeutic strategies.

Medical Education
Medical education: It is the education related to the practice of being a medical practitioner; either the initial training to become a physician(i.e., medical school and internship), additional training thereafter (e.g., residency and fellowship).
Medical education and training varies considerably across the world. Various teaching methodologies have been utilised in medical education, which is an active area of educational research.
These are divided into two parts: Entry Level and Postgraduate Level and often Even there’s a third part (i.e. To Continue Education).
Entry-level medical education programs are tertiary-level courses undertaken at a medical school. Depending on jurisdiction and university, these may be either undergraduate-entry (most of Europe, India, China), or graduate-entry programs (mainly Australia, Canada, United States).
In general, initial training is taken at medical school. Traditionally initial medical education is divided between preclinical and clinical studies. The former consists of the basic sciences such as anatomy, physiology, biochemistry, pharmacology, pathology. The latter consists of teaching in the various areas of clinical medicine such as internal medicine, pediatrics, obstetrics and gynecology, psychiatry, general practice and surgery. However, medical programs are using systems-based curricula in which learning is integrated, and several institutions do this. In the United States, until quite recently, the requirements for the M.D. degree did not include even one course in human nutrition. Today, this omission has been rectified; at least to the extent that one such course is required
Following completion of entry-level training, newly graduated doctors are often required to undertake a period of supervised practice before full registration is granted; this is most often of one-year duration and may be referred to as an "internship" or "provisional registration" or "residency".
Further training in a particular field of medicine may be undertaken. In some jurisdictions, this is commenced immediately following completion of entry-level training, while other jurisdictions require junior doctors to undertake generalist (unstreamed) training for a number of years before commencing specialisation.
Education theory itself is becoming an integral part of postgraduate medical training. Formal qualifications in education are also becoming the norm for medical school educators, who are increasingly accountable for their students.
Nowadays, Medical Education can also be gained online with Learning Management Systems and Virtual learning Environments such as EdX and other Online OpenCoursewaves.

National and Global Institutes

India: The All India Institutes of Medical Sciences (AIIMS) are a group of autonomous public medical colleges of higher education. These institutes have been declared by Act of Parliament as institutions of national importance. AIIMS New Delhi, the fore-runner parent excellence institution, was established in 1956.

United States: The National Institutes of Health (NIH) is a biomedical research facility primarily located in Bethesda, Maryland. An agency of the United States Department of Health and Human Services, it is the primary agency of the United States government responsible for biomedical and health-related research. The NIH both conducts its own scientific research through its Intramural Research Program (IRP) and provides major biomedical research funding to non-NIH research facilities through its Extramural Research Program.
With 1,200 principal investigators and more than 4,000 postdoctoral fellows in basic, translational, and clinical research, the IRP is the largest biomedical research institution in the world, while, as of 2003, the extramural arm provided 28% of biomedical research funding spent annually in the U.S., or about US$26.4 billion.
The NIH comprises 27 separate institutes and centers that conduct research in different disciplines of biomedical science. The IRP is responsible for many scientific accomplishments, including the discovery of fluoride to prevent tooth decay, the use of lithium to manage bipolar disorder, and the creation of vaccines against hepatitis, Haemophilus influenzae (HIB) and human papillomavirus(HPV).

China: The National Health Research Institutes in Zhunan Township, Miaoli County, Taiwan, is a non-profit foundation dedicated to medical research and improved healthcare in Taiwan. Established by the Republic of China government in 1995, NHRI is under the supervision of the Ministry of Health and Welfare.

Global: Some of the World’s Top Universities such as Harvard, Yale, Princeton, Wiscousin, Georgia etc. have their Global Health Institutes its Suggested to read a bit about them on Wiki.

Private vs. Public Health
Public Hospitals:  These are the healthcare centres which are operated by the Government for Service to the public. They can’t turn anyone away, if they knock their doors. They are cheap and a lot more affordable than private hospitals. It is a big and has got a lot more beds and employees as compared to Private Hospitals but patient-to-doctor Ratio is poor.
Private Hospitals: These are the healthcare centres which are operated by Individuals or Companies for Profit. They are smaller than Public Hospitals and Provide much more personalized care as compared to Public Hospitals. Nurses here take care for 1-2 Patients a time instead of tonnes of patients at once like in case of Public Hospitals. Wait times tend to be shorter and level of technology tends to be higher than Public Hospitals. They might refuse you to enter if you don’t have sufficient funds, they might not accept all forms of insurance, and they tend to be more expensive (as compared to private hospitals) in general.
According to the 2014 American Hospital Association Annual Survey, there are 5,686 hospitals in the United States. Of that total, 2,904 are public hospitals, and 1,060 are private. There are a total of 795,603 staffed beds in public hospitals and 118,910 staffed beds in private hospitals. Public hospitals had about 33.6 million admissions annually while private hospitals had about 1.8 million admissions annually.

AS FOR SUCCESSES AND SHORTCOMINGS THERE’S A HUGE LIST THUS, WE SUGGEST TO RESEARCH
 #Spreadthepwaathogen
From Hippocates to the Four Humours : Classical Views of Disease
The Classical views of Diseases include the Works of Hippocrates: The Theory of Humorism (which originated as part of Indian Ayurvedic System), The Four Temperaments (The Proto Psychological Theory which was proposed by Hippocrates), Wu Xian (Chinese) and TECHNICALLY the Greek Legend of Asclepius (whose Rob said to be the Rod of Asclepius remains to be the symbol of Medicine today.).
Humorism was a system of medicine detailing the makeup and workings of the human body, adopted by the Indian Ayurveda system of medicine, Ancient Greek and Roman physicians and philosophers, positing that an excess or deficiency of any of four distinct bodily fluids in a person—known as humors or humours—directly influences their temperament and health. The humoralist system of medicine is highly individualistic, for each individual patient was said to have their own unique humoral composition. Moreover, it resembled a holistic approach to medicine as the link between mental and physical processes was emphasized by this framework. From Hippocrates onward, the humoral theory was adopted by Greek, Roman and Persian physicians, and became the most commonly held view of the human body among European physicians until the advent of modern medical research in the nineteenth century. The concept has not been used in medicine since then.
The Four Humours along with the Temperaments and Seasons which were developed upon them by Hippocrates and Indian Ayurvedic experts:
Humour
Season
Element
Organ
Quality
Temperament
Temperament Characteristics
Ancient Name
Blood
Spring
Air
Heart
Warm and Moist
Sanguine
Optimistic and Social
Sanguis
Yellow Bile
Summer
Fire
Liver
Warm and Dry
Choleric
Short tempered or irritable
Khole
Black Bile
Autumn
Earth
Spleen
Cold and Dry
Melancholic
Analytical and Quiet
Melaina Khole
Phlegm
Winter
water
Brain
Cold and Moist
phlegmatic
Relaxed and Peaceful
phlegma

This Table anyhow provides improved info, According to the Original Humorism Theory, Blood was believed to be released by the Liver. Excess of Yellow Bile was believed to cause Anger which is the reason why in many Languages: Anger is written as Colere (French) and colera (Spanish).
Although advances in cellular pathology and chemistry discredited humoralism by the nineteenth century, the theory had dominated Western medical thinking for more than 2,000 years.
Hippocrates: He was a Greek physician of the Age of Pericles (Classical Greece), and is considered one of the most outstanding figures in the history of medicine. He is referred to as the "Father of Western Medicine" in recognition of his lasting contributions to the field as the founder of the Hippocratic School of Medicine. This intellectual school revolutionized medicine in ancient Greece, establishing it as a discipline distinct from other fields with which it had traditionally been associated (theurgy and philosophy), thus establishing medicine as a profession.
Asclepius: He was a god of medicine in ancient Greek religion and mythology. Asclepius represents the healing aspect of the medical arts; his daughters are Hygieia ("Hygiene", the goddess/personification of health, cleanliness, and sanitation), Iaso (the goddess of recuperation from illness), Aceso (the goddess of the healing process), Aglae (the goddess of beauty, splendor, glory, magnificence, and adornment), and Panacea (the goddess of universal remedy). He was associated with the Roman/Etruscan god Vediovis. He was one of Apollo's sons, sharing with Apollo the epithet Paean ("the Healer.Those physicians and attendants who served this god were known as the Therapeutae of Asclepius [These include Plato, Julian(The Emperor). Dionysus, Aelian etc.].
Another Example of Classical View of Medicine in Ayurved is The Doshas.
According to this concept in Ayurvedic Medicine (Dosha), Health can exist only if there’s an equal balance of three doshas in the Human Body. These Three Doshas are:
1) Vatta(or the Wind): It is the dosha which is the impulse principle necessary to mobilise the Nervous System.
2) Pitta: It is something that is secreted between the Stomach and Bowels [i.e. (today)Bile].  And flowing through the Liver, and permeating Spleen, heart, eyes and Skin. Its main Quality is heat. It is the energy principle which uses bile for Digestion of food and to enhance metabolism.
3) Kapha: The Bodily nutrient which is said to be the principle bodily fluid which maintains Lubrication and Carrier of Nutrients throughout the Body.
Wu Xing:  It is also known as the Five Elements, Five Phases, the Five Agents, the Five Movements, Five Processes, and the Five Steps/Stages, is a fivefold conceptual scheme that many traditional Chinese fields used to explain a wide array of phenomena, from cosmic cycles to the interaction between internal organs, and from the succession of political regimes to the properties of medicinal drugs. The "Five Phases" are Wood , Fire ,Earth , Metal , and Water. This order of presentation is known as the "mutual generation" sequence. In the order of "mutual overcoming" they are Wood, Earth, Water, Fire, and Metal. 
The system of five phases was used for describing interactions and relationships between phenomena. After it came to maturity in the second or first century BCE during the Han dynasty, this device was employed in many fields of early Chinese thought, including seemingly disparate fields such as geomancy or Feng shui, astrology, traditional Chinese medicine, music, military strategy and martial arts. The system is still used as a reference in some forms of complementary and alternative medicine and martial arts.
Distinguishing Between Sickness, Illness and Disease
Disease
Illness
Sickness
It is a pathological process, most often physical as in throat infection, or cancer of the bronchus, sometimes undetermined in origin, as in schizophrenia. The quality which identifies disease is some deviation from a biological norm. There is an objectivity about disease which doctors are able to see, touch, measure, smell.
It is a feeling, an experience of unhealth which is entirely personal, interior to the person of the patient. Often it accompanies disease, but the disease may be undeclared, as in the early stages of cancer or tuberculosis or diabetes. Sometimes illness exists where no disease can be found. Traditional medical education has made the deafening silence of illness-in-the-absence-of-disease unbearable to the clinician.
It is the external and public mode of unhealth. Sickness is a social role, a status, a negotiated position in the world, a bargain struck between the person henceforward called ‘sick’, and a society which is prepared to recognise and sustain him. The security of this role depends on a number of factors, not least the possession of that much treasured gift, the disease. Sickness based on illness alone is a most uncertain status. But even the possession of disease does not guarantee equity in sickness. 
Example: Common Cold WHICH CAN BE EASILY INTERPRETED BY LOOKING ON THE VICTIM.
Examples are: When you’re in Mental Depression which is extremely Personal, When you have Minor leg pain, Headache which isn’t much projected physically.
Example: When you go on a leave for an entire week from Any Institution.
Here the Doctor can feel your heartbeat, Check your temperature to get readings of the INSANITY/Degree of the Disease.
Here The Doctor can’t get any specific measurements.
Here, It is much like Illness but just that here the Public might Force you to goto a Doctor (Unlike In Illness).

According to Ancient Greeks, They clearly Differentiated Disease, Illness and Sickness by appointing different Gods to each of these: Asclepius for Diseases, Laso for Illness and Algea for Sickness.
Advances in the 19th and 20th Century
Traditional ideas of the body, whereby women were regarded as smaller versions of men, and 'turned outside in' (i.e. with internal rather than external sexual organs) were gradually superseded by a binary concept of sexual determinism, in which difference governed all aspects of physiology, health and social behaviour. As the body was also defined as a closed system of energy, 
physical, mental and reproductive expenditure were held to be in competition. Hence the notions that male sexual 'excess' led to debility and female reproductive health was damaged by intellectual study. Hence, too, must have derived the Victorian prescription for many ailments: rest.
In the Early Victorian Period (1830s-1850s), Disease transmission was largely understood as a matter of inherited susceptibility, and Water and Air Bourne Diseases were not accepted.
The 1848 edition of Buchan's Domestic Medicine, with its coloured frontispiece showing the symptoms of smallpox, scarlet fever and measles, listed among the general causes of illness 'diseased parents', night air, sedentary habits, anger, wet feet and abrupt changes of temperature. The causes of fever included injury, bad air, violent emotion, irregular bowels and extremes of heat and cold. Cholera, shortly to be epidemic in many British cities, was said to be caused by rancid or putrid food, by 'cold fruits' such as cucumbers and melons, and by passionate fear or rage.
Scientific developments in the 19th century had a major impact on understanding health and disease, as experimental research resulted in new knowledge in histology, pathology and microbiology. Few of these advances took place in Britain, where medical practice was rarely linked to scientific work and there was public hostility to the animal vivisection on which many experiments relied. The biochemical understanding of physiology began in Germany in the 1850s, together with significant work on vision and the neuromuscular system, while in France Louis Pasteur laid the foundations of the germ theory of disease based on the identification of micro-bacterial organisms. By the end of the century a new understanding of biology was thus coming into being, ushering in a new emphasis on rigorous hygiene and fresh air, and a long-lasting fear of invisible contagion from the unwashed multitude, toilet seats and shared utensils. British patent applications around 1900 include devices for avoiding infection via the communion chalice and the new-fangled telephone.
With Technological Advances all the processes were underpinned, from the ophthalmoscope (an Instrument used to see through/into the eye) to the Microscope (to look upon microorganisms), to instruments like kymograph(to measure blood pressure and muscular contraction.) The Stethoscope was invented in France in 1817 which aided diagnosis of respiratory and cardiac disorders.  However, the most famous British visual image, Luke Fildes's The Doctor (exhibited at the Royal Academy in 1891) shows a medical man with virtually no 'modern' equipment.
The Invention of immunization and eradication of Smallpox are also examples of some of the Advances that took place in Public Health. Thanks to Edward Jenner.
Surgeries advanced through the 19th Century, With the invention of Anaesthesia (oxygen Supplier). Notable Public Demonstrations of the effects of ether in London in October 1846 and the use of Chloroform for the Queen’s eighth confinement in 1853.
Anaesthetics enabled surgeons to perform more sophisticated operations in addition to the traditional amputations. Specialised surgical instruments and techniques followed, for some time with mixed results, as unsterile equipment frequently led to fatal infection.
Antiseptic surgical procedures based on the practical application of Pasteur's laboratory work were developed by Joseph Lister (1827-1912) using carbolic acid (phenol) from 1869 in Edinburgh and in 1877 in London. Aseptic procedures followed, involving sterilisation of whole environments. Successful outcomes, such as Edward VII's appendicitis operation on the eve of his scheduled coronation, helped pave the way for the 20th-century era of heroic surgery.
In 1895, at the end of the era, came Wilhelm Roentgen's discovery of X-rays, and in due course the photo of Roentgen's wife's hand became a potent sign of medical advance through scientific instruments. But overall the 19th century is notable more for systematic monitoring of disease aetiology than for curative treatment.
Throughout the era, since disorders of both body and mind were believed to be heritable conditions, the chronic sick, the mentally impaired and the deranged were vigorously urged against marriage and parenthood.
Agents of Infection and Modes of Transmission
The process of infection can be broken down into stages, each of which can be blocked by different defence mechanisms. In the first stage, a new host is exposed to infectious particles shed by an infected individual. The number, route, mode of transmission, and stability of an infectious agent outside the host determines its infectivity. Some pathogens, such as anthrax, are spread by spores that are highly resistant to heat and drying, while others, such as the human (HIV), are spread only by the exchange of bodily fluids or tissues because they are unable to survive as infectious agents outside the body.
The mammalian body is susceptible to infection by many pathogens, which must first make contact with the host and then establish a focus of infection in order to cause infectious disease. To establish an infection, the pathogen must first colonize the skin or the internal mucosal surfaces of the respiratory, gastrointestinal, or urogenital tracts and then overcome or bypass the innate immune defences associated with the epithelia and underlying tissues. If it succeeds in doing this, it will provoke an adaptive immune response that will take effect after several days and will usually clear the infection. Pathogens differ greatly in their lifestyles and means of pathogenesis, requiring an equally diverse set of defensive responses from the host immune system.
Actually, there are more than a few types of Infection Agents, In Almost all of these cases these are microorganisms. We could have different types of Microorganisms based o their Size, Shape etc. Bacteria and protozoa are microscopic one-celled organisms, while viruses are even smaller. Fungi grow like plants and helminths resemble worms.

Modes of Pathogen Transmission: The Transmission involves the following stages:
1) Escape from the host or reservoir of infection (where the infectious agent normally lives and multiplies).
2) Transport to the new host.
3) Entry to the new host.
4) Escape from the new host.
Different pathogens have different modes of transmission. For example respiratory pathogens are usually airborne and intestinal pathogens are usually spread by water or food.
There are basically two modes of Pathogen transmission:
1) Direct Transmission: It occurs when a pathogen is transferred directly from an individual to you. It happens in the case of HBV, One might get infected with HBV if he had an open wound which was subjected to HBV infected blood. A person who has got cold might wipe their nose with their bare hands, The Mucus would be dripping with virus and then when we would shake hands with anyone else, The Virus might get into his nose (through his hands) as well. Hepatitis B and HIV are examples of Direct Transmission through Saliva or Sex. Measles, Tuberculosis and Mumps are examples of the transmission through Air (sneezing).
2) Indirect Transmission: It occurs when an inanimate object serves as a temporary reservoir for the infectious agent.  For example, you could become infected with HBV if you come into contact with equipment that has dried infectious blood on it. Microorganisms need food for their growth and survival, They can get into our food any time (This food-chain is known as plough to plate).Once They get into our food They can get into our stomach and cause diseases. Some Diseases such as Cholera and Typhoid are caused due to drinking Contaminated Water. Insects are responsible for Spreading many diseases, The Female Anopheles mosquito carries the Plasmodium Falciparum Protozoan (It gets into the body as soon as the mosquito haves a Blood Meal.). The Bubonic Plague (Black Death) is a bacterial disease of rodents caused by Yersinia pestis. Formites (These are non-living) are basically the algae which is carried by bedding, Towels, toys and barbed wire.

Detecting and Managing Epidemics
Clinicians are often in the best position to recognize an outbreak of disease; sometimes they see an unusually high number of people with the same disease and at other times patients report that they know other people with similar symptoms. Even if the clinician does not suspect an outbreak, his reporting contributes to the detection of outbreaks. Filling in discharge summaries and death certificates, and reporting cases of notifiable disease all contribute to health surveillance. Ensuring that the forms are completed accurately and transferred in a timely fashion makes a major contribution to outbreak detection and general health surveillance.
Depending on the type of organism involved, the conditions of spread and the target population, outbreaks can be acute and fast-moving, such as gastroenteritis in a nursery school or long-term care home, or they can evolve more slowly, such as the AIDS pandemic. While public health authorities are ultimately responsible for ensuring the detection and control of outbreaks, clinicians are major players in this area because they are usually the first point of contact with the affected population. Likewise, hospital infection control teams rely on the cooperation of clinicians in preventing infections. The basic steps in outbreak control and management are:
1. Establish the existence of an outbreak: This refers to identifying that there is to be an epidemic before it develops into a full epidemic. This is especially true of rare diseases and diseases in small populations, where an absolute increase of a very small number of cases could represent a large relative increase in an illness in the population. For instance, in a community where there are usually two cases of a given disease in one month, four cases in one month (relative increase of 100%, absolute increase of 2 cases) may or may not constitute an outbreak. In such instances, it can be very difficult to decide how much time and money to spend on investigating something that might be just a chance occurrence. Consultation with epidemiologists or statisticians may be required, but the statistical techniques for assessing the influence of chance in disease clusters are still in development. A pandemic can be declared only after a careful evaluation by WHO.
2. Define what constitutes a case and identify cases as they occur: A crucial early step in investigating a possible outbreak is to define what constitutes a case, as the case definition will be used in the search for more cases, who will then be questioned about their exposures. The case definition describes precisely the symptoms, signs, history, or test results that indicate a probable case of disease. Clinicians may be asked to help in the search to uncover all cases, and they may also have valuable information linking the cases, which can suggest a possible cause. Because of biological variation, the presenting symptoms and signs for cases of any illness vary.
3. Formulate hypotheses on the causes, and implement initial control measures: Using the information gathered in the initial steps of the investigation, public health professionals describe the epidemic in time, place, and person. An outbreak progresses, they may draw an epidemic curve to track its evolution in. They describe in detail the circumstances of the outbreak and the demographic characteristics of the people affected. Thus, the patterns described usually indicate the likely source of the outbreak and the population at high risk. This is generally sufficient to suggest some initial control measures.
4. Test the hypotheses through analysis of surveillance data or special studies: Once there is a hypothesis about the cause of the outbreak, it should be tested. If removing the suspected source is followed by a decline in the outbreak, the hypothesis may be correct, although the decline could still be serendipitous. Cross-sectional studies can be carried out in the case of food-borne outbreaks in a limited population. For instance, in the case of an outbreak associated with a social gathering, guests can be asked about symptoms and about foods eaten to identify particular foods that are likely to have been contaminated.
5. Draw conclusions and re-adjust hypotheses and control measures if needed: Once the cause of the outbreak has been confirmed, the initial control measures may need to be adjusted. If the source cannot be identified, more epidemiological detective work may be required. Based on the results of the outbreak investigation, it may also be possible to recommend action to prevent future similar outbreaks.
6. Plan for long-term prevention and control: Outbreak investigations should be designed to indicate the possible long-term preventive actions and ways of improving response to future similar outbreaks. When available and safe, active immunization is a very successful way of preventing outbreaks of infectious disease. As long as the vaccine provides lasting immunity, the person remains protected, at least to some degree. Vaccines have created an opportunity for eradication of disease. Smallpox, a virulent and once common illness that afflicted humans for centuries, was eradicated in 1977. Currently, the World Health Organization is working to eradicate polio, which, in 2010, is endemic in only four countries, although still appears in epidemic form in twenty-three.
AS FOR THE SEARCH OF CURES AND TREATMENTS, ITS WAY TOO LONG THUS RESEARCH YOURSELF
Social Responses to Disease
How a society responds to diseases is the subject of medical sociology.
A condition may be considered a disease in some cultures or eras but not in others. For example, obesity can represent wealth and abundance, and is a status symbol in famine-prone areas and some places hard-hit by HIV/AIDS. Epilepsy (A group of Neurological Diseases caused by genetic mutations.) is considered a sign of spiritual gifts among the Hmong People (Those living in the mountainous regions of China, Laos, Vietnam and Thailand).
Sickness confers the social legitimization of certain benefits, such as illness benefits, work avoidance, and being looked after by others. The person who is sick takes on a social role called the sick role. A person who responds to a dreaded disease, such as cancer, in a culturally acceptable fashion may be publicly and privately honored with higher social status. In return for these benefits, the sick person is obligated to seek treatment and work to become well once more. As a comparison, consider pregnancy, which is not interpreted as a disease or sickness, even if the mother and baby may both benefit from medical care.
Most religions grant exceptions from religious duties to people who are sick. For example, one whose life would be endangered by fasting on Yom Kippur(It is said to be the Day of Atonement, The Holiest day in Judaism) or during Ramadan (According to Islam, The ninth month of their Calendar, Which marks fasting to the Muhammad) is exempted from the requirement, or even forbidden from participating. People who are sick are also exempted from social duties. For example, ill health is the only socially acceptable reason for an American to refuse an invitation to the White House.
The identification of a condition as a disease, rather than as simply a variation of human structure or function, can have significant social or economic implications. The controversial recognitions as diseases of repetitive stress injury (RSI) and post-traumatic stress disorder (also known as "Soldier's heart", "shell shock", and "combat fatigue") has had a number of positive and negative effects on the financial and other responsibilities of governments, corporations and institutions towards individuals, as well as on the individuals themselves. The social implication of viewing aging as a disease could be profound, though this classification is not yet widespread.
Lepers were people who were historically shunned because they had an infectious disease, and the term "leper" still evokes social stigma. Fear of disease can still be a widespread social phenomenon, though not all diseases evoke extreme social stigma.
Social standing and economic status affect health. Diseases of poverty are diseases that are associated with poverty and low social status; diseases of affluence are diseases that are associated with high social and economic status. Which diseases are associated with which states varies according to time, place, and technology. Some diseases, such as diabetes mellitus, may be associated with both poverty (poor food choices) and affluence (long lifespans and sedentary lifestyles), through different mechanisms. The term diseases describes diseases that are more common among older people. For example, cancer is far more common in societies in which most members live until they reach the age of 80 than in societies in which most members die before they reach the age of 50.

Diseases to Explore
Smallpox: It is an infectious Disease Caused by either of two virus variants, Variola Major and Variola Minor.  The disease was originally known in English as the "pox" or "red plague"; the term "smallpox" was first used in Britain in the 15th century to distinguish variola from the "great pox" (syphilis). The last naturally occurring case of smallpox (Variola minor) was diagnosed on 26 October 1977.
Infection with smallpox is focused in small blood vessels of the skin and in the mouth and throat before disseminating. In the skin it results in a characteristic maculopapular rash and, later, raised fluid-filled blisters. V. major produced a more serious disease and had an overall mortality rate of 30–35 percent. V. minor caused a milder form of disease (also known as alastrim, cottonpox, milkpox, whitepox, and Cuban itch) which killed about 1 percent of its victims. Long-term complications of V. major infection included characteristic scars, commonly on the face, which occur in 65–85 percent of survivors. Blindness resulting from corneal ulceration and scarring, and limb deformities due to arthritis and osteomyelitis were less common complications, seen in about 2–5 percent of cases.
Smallpox is believed to have emerged in human populations about 10,000 BC. The earliest physical evidence of it is probably the pustular rash on the mummified body of Pharaoh Ramses V of Egypt. The disease killed an estimated 400,000 Europeans annually during the closing years of the 18th century (including five reigning monarchs),  and was responsible for a third of all blindness. Of all those infected, 20–60 percent—and over 80 percent of infected children—died from the disease. Smallpox was responsible for an estimated 300–500 million deaths during the 20th century. As recently as 1967, the World Health Organization (WHO) estimated that 15 million people contracted the disease and that two million died in that year.
After vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the global eradication of smallpox in 1979. Smallpox is one of two infectious diseases to have been eradicated, the other being rinderpest (An infectious disease very similar to Smallpox but caused in animals.), which was declared, eradicated in 2011.
The incubation period between contraction and the first obvious symptoms of the disease is around 12 days. Once inhaled, variola major virus invades the oropharyngeal (mouth and throat) or the respiratory mucosa, migrates to regional lymph nodes, and begins to multiply. In the initial growth phase the virus seems to move from cell to cell, but around the 12th day, lysis of many infected cells occurs and the virus is found in the bloodstream in large numbers (this is called viremia), and a second wave of multiplication occurs in the spleen, bone marrow, and lymph nodes. The initial or prodromal symptoms are similar to other viral diseases such as influenza and the common cold:fever of at least 38.3 °C (101 °F), muscle pain, malaise, headache and prostration. As the digestive tract is commonly involved, nausea and vomiting and backache often occur. The prodrome, or preeruptive stage, usually lasts 2–4 days. By days 12–15 the first visible lesions—small reddish spots called enanthem—appear on mucous membranes of the mouth, tongue, palate, and throat, and temperature falls to near normal. These lesions rapidly enlarge and rupture, releasing large amounts of virus into the saliva.
Bubonic Plague:  is one of three types of bacterial infection caused by Yersinia pestis. Three to seven days after exposure to the bacteria flu like symptoms develop. This includes fever, headaches, and vomiting. Swollen and painful lymph nodes occur in the area closest to where the bacteria entered the skin. Occasionally the swollen lymph nodes may break open.
The three types of plague are the result of the route of infection: bubonic plague, septicemic plague, and pneumonic plague. Bubonic plague is mainly spread by infected fleas from small animals. It may also result from exposure to the body fluids from a dead plague infected animal. In the bubonic form of plague, the bacteria enter through the skin through a flea bite and travel via thelymphatic vessels to a lymph node, causing it to swell. Diagnosis is by finding the bacteria in the blood, sputum, or fluid from lymph nodes.
Prevention is through public health measures such as not handling dead animals in areas where plague is common. Vaccines have not been found to be very useful for plague prevention. Several antibiotics are effective for treatment including streptomycin, gentamicin, and doxycycline. Without treatment it results in the death of 30% to 90% of those infected. Death if it occurs is typically within ten days. With treatment the risk of death is around 10%.Globally in 2013 there were about 750 documented cases which resulted in 126 deaths. The disease is most common in Africa.
Plague is believed to be the cause of the Black Death that swept through Asia, Europe, and Africa in the 14th century and killed an estimated 50 million people. This was about 25% to 60% of the European population. Because the plague killed so many of the working population, wages rose due to the demand for labor. Some historians see this as a turning point in European economic development.
The best-known symptom of bubonic plague is one or more infected, enlarged, and painful lymph nodes, known as buboes. After being transmitted via the bite of an infected flea, the Y. pestis bacteria become localized in an inflamed lymph node where they begin to colonize and reproduce. Buboes associated with the bubonic plague are commonly found in the armpits, upper femoral, groin and neck region.
Bubonic Plague is an infection of the lymphatic system (The part of Circulatory system which supplies water to plasma in the blood.).
Cholera: It is an infectious intestinal disorder. It is common in southern Asia, and outbreaks also occur occasionally in other parts of the world. Cholera is caused by a comma-shaped bacterium called Vibrio cholerae. The microorganism is transmitted by water or food that has been contaminated with the feces (solid body wastes) of people who have the disease.

Cholera occurs when Vibrio cholerae enters the intestines and releases cholera toxin. The toxin causes the intestine to secrete large amounts of water and salt. Because the intestine cannot absorb the water and salt at the rate they are secreted, the patient suffers severe diarrhea. This loss of fluid causes severe dehydration and changes in the body chemistry. If untreated, the illness can lead to shock and eventually death. With proper treatment, cholera lasts only a few days.

Doctors treat cholera with special solutions that help replace the patient's lost fluids. The solutions may be taken orally or intravenously (by injection). Intravenous treatments are more effective, but they often are not available in rural areas where the illness frequently occurs. An easily prepared household solution for treating cholera consists of 5 grams (1 teaspoon) of salt and 20 grams (4 teaspoons) of sugar per 1 liter (0.95 quart) of water. The amount of fluid given to the patient should match the amount lost in diarrhea.

Prevention of cholera requires adequate sanitation facilities. A vaccine against the illness has been developed, but it is not very effective. People who travel in areas where cholera is widespread should not drink the local water. In addition, they should cook all foods that may have been exposed to water.
It can also be cured with Electrolysis to balance the amount of potassium in the Body. The antibiotics which were used to cure Cholera were heavily affected by Antibiotic Resistance.
The word cholera is from Greek word which means "bile". Cholera likely has its origins in the Indian subcontinent; it has been prevalent in the Ganges delta since ancient times. Early outbreaks in the Indian subcontinent are believed to have been the result of poor living conditions as well as the presence of pools of still water; both of which are ideal living conditions for cholera to thrive. The disease first spread by trade routes (land and sea) to Russia in 1817, later to the rest of Europe, and from Europe to North America and the rest of the world. Seven cholera pandemics have occurred in the past 200 years, with the seventh pandemic originating in Indonesia in 1961.
Polio (or Poliomyelitis): is an infectious disese caused by the poliovirus. In about 0.5% of cases there is muscle weakness resulting in an inability to move. This can occur over a few hours to few days. The weakness most often involves the legs but may less commonly involve the muscles of the head, neck and diaphragm. Many but not all people fully recover. In those with muscle weakness about 2% to 5% of children and 15% to 30% of adults die. Another 25% of people have minor symptoms such as fever and a sore throat and up to 5% have headache, neck stiffness and pains in the arms and legs. These people are usually back to normal within one or two weeks. In up to 70% of infections there are no symptoms. Years after recovery post-polio syndrome may occur, with a slow development of muscle weakness similar to what the person had during the initial infection.
Poliovirus is usually spread from person to person through infected feces entering the mouth. It may also be spread by food or water containing human feces and less commonly from infected saliva. Those who are infected may spread the disease for up to six weeks even if no symptoms are present. The disease may be diagnosed by finding the virus in the feces or detecting antibodiesagainst it in the blood.
The disease is preventable with the polio vaccine; however, a number of doses are required for it to be effective. The United States Center for Disease Control recommends polio vaccination boosters for travelers and those who live in countries where the disease is occurring.[4] Once infected there is no specific treatment. In 2013 polio affected 416 people down from 350,000 cases in 1988. In 2014 the disease was only spreading between people in Afghanistan, Nigeria, and Pakistan. In 2015 Nigeria had stopped the spread of wild poliovirus.[5]
Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art. The disease was first recognized as a distinct condition by Michael Underwood in 1789 and the virus that causes it was first identified in 1908 by Karl Landsteiner. Major outbreaks started to occur in the late 19th century in Europe and the United States. In the 20th century it became one of the most worrying childhood diseases in these areas. The first polio vaccine was developed in the 1950s by Jonas Salk. It is hoped that vaccination efforts and early detection of cases will result in global eradication of the disease by 2018. In 2013; however, there were reports of new cases in Syria and in May 2014, the World Health Organization declared a public health emergency of international concern due to outbreaks of the disease in Asia, Africa and the Middle East. The disease does not naturally occur in any other animals.
Two Basic Patterns of Polio Infection are that which infects through the Central Nervous System and the other which infects through the Immune system.
Polio is caused by a group of RNA viruses which colonize the gastrointestinal Tracts specifically thr oropharynx and intestine.
In 1950, William Hammon at the University of Pittsburgh purified thegamma globulin component of the blood plasma of polio survivors. Hammon proposed the gamma globulin, which contained antibodies to poliovirus, could be used to halt poliovirus infection, prevent disease, and reduce the severity of disease in other patients who had contracted polio. The results of a large clinical trial were promising; the gamma globulin was shown to be about 80% effective in preventing the development of paralytic poliomyelitis. It was also shown to reduce the severity of the disease in patients who developed polio. Due to the limited supply of blood plasma gamma globulin was later deemed impractical for widespread use and the medical community focused on the development of a polio vaccine.
Two types of vaccine are used throughout the world to combat polio. Both types induce immunity to polio, efficiently blocking person-to-person transmission of wild poliovirus, thereby protecting both individual vaccine recipients and the wider community (so-called herd). The Vaccine contains Weakened Polio Virus.
There is no treatment or cure for Polio once it approaches and gets into someone’s body.

Syphilis: It is a sexually transmitted infection caused by the spiro-chetebacterium Treponema pallidum subspeciespallidum. The primary route of transmission is through sexual contact; it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis. Other human diseases caused by related Treponema palliduminclude yaws (subspeciespertenue), pinta(subspecies carateum), and bejel (subspeciesendemicum).
The signs and symptoms of syphilis vary depending in which of the four stages it presents (primary, secondary, latent, and tertiary). The primary stage classically presents with a single chancre [(a firm, painless, non-itchy skin ulceration)In the penis or Vagina], secondary syphilis with a diffuse rash which frequently involves the palms of the hands and soles of the feet, latent syphilis with little to no symptoms, and tertiary syphilis with gummas, neurological, or cardiac symptoms. It has, however, been known as "the great imitator" due to its frequent atypical presentations. Diagnosis is usually made by using blood tests; however, the bacteria can also be detected using dark. Syphilis can be effectively treated with antibiotics, specifically the preferred intramuscular benzathine penicillin G (orpenicillin G potassium given intravenously for neurosyphilis), or else ceftriaxone, and in those who have a severe penicillin allergy, oral doxycycline or azithromycin.
Syphilis is thought to have infected 12 million additional people worldwide in 1999, with greater than 90% of cases in the developing world. After decreasing dramatically since the widespread availability of penicillin in the 1940s, rates of infection have increased since the turn of the millennium in many countries, often in combination with human immunodeficiency virus (HIV). This has been attributed partly to increased promiscuity, prostitution, decreasing use of condoms, and unsafe sexual practices among men who have sex with men. In 2015, Cuba became the first country in the world to eradicate mother-to-child transmission syphilis.

Tuberculosis:  is a widespread, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis generally affects the lungs, but can also affect other parts of the body. It is spread through the air when people who have an active TB infection cough, sneeze, or otherwise transmit respiratory fluids through the air. Most infections do not have symptoms, known as latent tuberculosis. About one in ten latent infections eventually progresses to active disease which, if left untreated, kills more than 50% of those so infected.
The classic symptoms of active TB infection are a chronic cough with blood sputum, fever, night sweats, and weight loss (the last of these giving rise to the formerly common term for the disease, "consumption"). Infection of other organs causes a wide range of symptoms. Diagnosis of active TB relies on radiology (commonly chest X-rays), as well as microscopic examination and microbiological cultureof body fluids. Diagnosis of latent TB relies on the tuberculin skin test(TST) and/or blood tests. Treatment is difficult and requires administration of multiple antibiotics over a long period of time. Household, workplace and social contacts are also screened and treated if necessary. Antibiotic resistance is a growing problem inmultiple drug-resistant tuberculosis (MDR-TB) infections. Prevention relies on early detection and treatment of cases and on screening programs and vaccination with the bacillus Calmette-Guérin vaccine.
One-third of the world's population is thought to have been infected with M. tuberculosis, and new infections occur in about 1% of the population each year. In 2007, an estimated 13.7 million chronic cases were active globally, while in 2013, an estimated 9 million new cases occurred. In 2013 there were between 1.3 and 1.5 million associated deaths, most of which occurred in developing countries. The total number of tuberculosis cases has been decreasing since 2006, and new cases have decreased since 2002. The rate of tuberculosis in different areas varies across the globe; about 80% of the population in many Asian and African countries tests positive in tuberculin tests, while only 5–10% of the United States population tests positive. More people in the developing world contract tuberculosis because of a poor immune system, largely due to high rates of HIV infection and the corresponding development of AIDS.
Its basic Symptom is Chest Pain but in some cases it even gets outside the pulmonary Organs of the body.
Malaria: It is one of the most widespread and threatening parasitic diseases that affect human beings. The disease is common in tropical and subtropical regions. Malaria is caused by infection with parasites called Plasmodia (in the singular, Plasmodium). The parasites are one-celled organisms called protozoans. They are transmitted to human beings through the bite of the female Anopheles mosquito. Scientists estimate that about 500 million people are infected by malaria parasites and 1 million to 3 million people die from malaria each year. In addition to the deaths and suffering caused by malaria, the disease harms economic and social development in many countries. The disease slows economic growth because it makes many people too ill to work. In addition, the cost of treating malaria takes funds that are needed for other development.
A malarial attack lasts several hours and is accompanied by fever, headache, muscular pain, and nausea. The attacks come in a specific pattern. P. falciparum, P. vivax, and P. ovale cause attacks of chills and fever that return about every 48 hours. In P. malariae infections, symptoms return about every 72 hours. Between attacks, the infected individual usually feels better but is often weak and anemic.
The most serious disease is caused by P. falciparum. Victims become weaker with each attack, and many die if untreated. P. falciparum can cause severe complications, including respiratory problems, kidney damage, cerebral malaria, and placental malaria. In cerebral malaria, red blood cells infected with parasites stick to small blood vessels in the brain, causing seizures, coma, and death. Placental malaria interferes with the transfer of oxygen from the mother to the developing fetus, causing the unborn baby to develop poorly or die.
P. vivax and P. ovale are not associated with severe illness. Malaria due to these parasites may go away without treatment. However, the parasites can lie dormant and symptoms may reappear after a long period of apparent freedom from the disease. Severe illness with P. malariae is also uncommon.
The life cycle of the Plasmodium protozoan has three stages. The first stage begins when a mosquito bites someone who has malaria. Plasmodia enter the insect's body and reproduce in its stomach. The protozoan young find their way into the mosquito's saliva.
The second stage occurs after the mosquito bites another person. Plasmodia from the mosquito's saliva enter the person's blood. They travel to the liver, where they multiply and form clumps of parasites. After several days, these clumps burst and release new Plasmodia.
During the third stage, each Plasmodium invades a red blood cell, where it multiplies again. The infected blood cells eventually rupture and release large numbers of Plasmodia, which invade additional red blood cells. This cycle of invasion, multiplying, and cell rupture continues, causing the periodic attacks of fever that are typical of malaria. An attack occurs each time the red blood cells rupture. Some Plasmodia enter another mosquito's body when the mosquito bites an infected person, and their life cycle begins again.
Quinine, a drug derived from the bark of the cinchona plant, has been the main treatment for malaria since the 1600's. Most cases can be cured with quinine and similar, synthetic drugs, such as chloroquine, primaquine, and mefloquine. However, some varieties of P. falciparum have become resistant to these drugs. In the 1980's, scientists developed a drug called artemesinin from an herb used in traditional Chinese medicine. The drug is used with others to treat malaria and prevent development of resistant varieties of Plasmodia.
In 1998, the World Health Organization (WHO), an agency of the United Nations, launched a program to reduce malaria worldwide. The program emphasizes drug treatment and prevention of mosquito bites. It includes the limited use of insecticides, such as providing mosquito netting treated with insecticides for people's beds. Researchers are also working to develop a malaria vaccine.
Influenza: It is an infectious disease caused by the influenza virus. The disease is commonly called flu or grippe. The word influenza is sometimes used to refer generally to either influenza or similar illnesses. The symptoms of influenza include chills, fever, headache, body aches, and weakness. The symptoms usually disappear in about a week. The patient's resistance may be lowered, so that secondary infections, such as bacterial pneumonia, follow. Secondary infections are common in patients with immune system disorders or older adults.
There are three main types of influenza viruses: type A, type B, and type C. Types B and C appear to infect only human beings. Type A can infect people and certain animals, such as swine. The animals may then carry and transmit the disease to human beings. Each type of influenza occurs in many varieties called subtypes. The two most common type A subtypes are called H1N1 and H3N2. Subtypes of type A or B viruses cause most epidemics of influenza in human beings.
Influenza is mainly a respiratory disease. The virus is inhaled and comes in contact with cells of the upper air passages. It penetrates the cells that line these passages and reproduces. In time, new viruses are released from the infected cells and infect other cells along the respiratory tract. Influenza may spread deep within the lungs. The virus may also be carried away in exhaled air and infect other people. People may also become infected by touching something with the virus on it and then touching their mouth or nose. People develop immunity or resistance to influenza when the body produces substances called antibodies, which can attach themselves to influenza viruses and prevent them from infecting cells. But the virus may change its chemical composition so that the antibodies no longer work. The cells of the body must produce new kinds of antibodies. The body also can make cells called cytotoxic T cells, also called killer T cells, that recognize and kill cells infected with influenza virus. Simple hygiene practices, such as frequent hand washing, can help control the spread of influenza. However, the most effective means to prevent the spread of the disease is through vaccination. Most influenza vaccines are made from killed or weakened influenza viruses. Scientists are using genetic engineering techniques to produce better vaccines. In addition to vaccines, antiviral drugs, such as amantadine and rimantadine, are effective treatments for type A influenza infections, but not type B infections. Other drugs called neuraminidase inhibitors are effective in treating and preventing type A and B infections. Treatment of patients may include combating secondary infections, which cause most of the deaths associated with influenza. Physicians control these infections with antibiotics and other drugs.
Influenza tends to occur in epidemics. Each outbreak is caused by a virus slightly different from the earlier ones. Scientists often name the different strains (types) of the virus after the place where the strain was first identified. For example, A/Sydney/97 refers to a type A influenza strain that was first identified in Sydney, Australia, in 1997.
One of the worst global epidemics, called a pandemic, of influenza occurred in 1918-1919. In this pandemic, known as the Spanish flu, 25 million to 100 million people, including about 600,000 Americans, died. In 1957-1958, a strain called Asian flu caused a pandemic, as did the Hong Kong flu in 1968-1969. In each instance, the pandemics have been caused by new subtypes of the type A influenza virus.
Dengue: It is a mosquito-borne tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles. In a small proportion of cases, the disease develops into the life-threatening dengue hemorrhagic fever, resulting in bleeding, low levels of blood plateletsand blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs.
Dengue is transmitted by several species of mosquito within the genus Aedes, principally A. aegypti. The virus has five different types; infection with one type usually gives lifelong immunity to that type, but only short-term immunity to the others. Subsequent infection with a different type increases the risk of severe complications. As there is no commercially available vaccine, prevention is sought by reducing the habitat and the number of mosquitoes and limiting exposure to bites.
Treatment of acute dengue is supportive, using either oral or intravenous rehydration for mild or moderate disease, and intravenous fluids and blood transfusion for more severe cases. The number of cases of dengue fever has increased dramatically since the 1960s, with between 50 and 528 million people infected yearly. Early descriptions of the condition date from 1779, and its viral cause and transmission were understood by the early 20th century. Dengue has become a global problem since the Second World War and is endemic in more than 110 countries. Apart from eliminating the mosquitoes, work is ongoing on a dengue vaccine, as well as medication targeted directly at the virus.
The International Dengue Week is celebrated on 15 June every year, As an attempt to spread awareness about preventing Dengue.
Yellow Fever: It is an acute viral disease. In most cases, symptoms include fever, chills (Temperature increased from the limit at the Hypothalamus), loss of appetite (loss of the will to eat food), nausea (Discomfort in the upper part of the stomach), muscle pains particularly in the back, and headaches. Symptoms typically improve within five days. In some people within a day of improving, the fever comes back, abdominal pain occurs, and liver damage begins causing yellow skin. If this occurs, the risk of bleeding and kidney problems is also increased.
The disease is caused by the yellow fever virus and is spread by the bite of the female mosquito. It infects only humans, other primates, and several species of mosquitoes. In cities, it is spread primarily by mosquitoes of the Aedes aegypti species. The virus is an RNA virus of the genus Flavivirus. The disease may be difficult to tell apart from other illnesses, especially in the early stages. To confirm a suspected case, blood sample testing with polymerase chain reaction is required.
A safe and effective vaccine against yellow fever exists and some countries require vaccinations for travellers. Other efforts to prevent infection include reducing the population of the transmitting mosquito. In areas where yellow fever is common and vaccination is uncommon, early diagnosis of cases and immunization of large parts of the population is important to prevent outbreaks. Once infected, management is symptomatic with no specific measures effective against the virus. In those with severe disease, death occurs in about half of people without treatment.
Yellow fever causes 200,000 infections and 30,000 deaths every year, with nearly 90% of these occurring in Africa. Nearly a billion people live in an area of the world where the disease is common. It is common in tropical areas of South America and Africa, but not in Asia. Since the 1980s, the number of cases of yellow fever has been increasing. This is believed to be due to fewer people being immune, more people living in cities, people moving frequently, and changing climate. The disease originated in Africa, where it spread to South America through the slave trade in the 17th century. Since the 17th century, several major outbreaks of the disease have occurred in the Americas, Africa, and Europe. In the 18th and 19th centuries, yellow fever was seen as one of the most dangerous infectious diseases. In 1927 yellow fever virus became the first human virus to be isolated.

Leishmaniasis: It is a disease caused by protozoan parasites of the genus Leishmania and spread by the bite of certain types of sandflies. The disease can present in three main ways: cutaneous, mucocutaneous, or visceral leishmaniasis. The cutaneous form presents with skin ulcers, while the mucocutaneous form presents with ulcers of the skin, mouth, and nose, and the visceral form starts with skin ulcers and then later presents with fever, low red blood cells, and enlarged spleen and liver.
Infections in humans are caused by more than 20 species of Leishmania. Risk factors include poverty, malnutrition, deforestation, and urbanization. All three types can be diagnosed by seeing the parasites under the microscope. Additionally, visceral disease can be diagnosed by blood tests.
Leishmaniasis can be partly prevented by sleeping under nets treated with insecticide. Other measures include spraying insecticides to kill sandflies and treating people with the disease early to prevent further spread. The treatment needed is determined by where the disease is acquired, the species of Leishmania, and the type of infection. Some possible medications used for visceral disease include liposomal amphotericin B, a combination of pentavalent antimonials and paromomycin, andmiltefosine. For cutaneous disease, paromomycin, fluconazole, or pentamidine may be effective.
About 12 million people are currently infected in some 98 countries. About 2 million new cases and between 20 and 50 thousand deaths occur each year. About 200 million people in Asia, Africa, South and Central America, and southern Europe live in areas where the disease is common. The World Health Organization has obtained discounts on some medications to treat the disease. The disease may occur in a number of other animals, including dogs and rodents.
Hepatitis: It is an inflammation of the liver. The condition can be self-limiting or can progress to fibrosis (scarring), cirrhosis or liver cancer. Hepatitis viruses are the most common cause of hepatitis in the world but other infections, toxic substances (e.g. alcohol, certain drugs), and autoimmune diseases can also cause hepatitis.
There are 5 main hepatitis viruses, referred to as types A, B, C, D and E. These 5 types are of greatest concern because of the burden of illness and death they cause and the potential for outbreaks and epidemic spread. In particular, types B and C lead to chronic disease in hundreds of millions of people and, together, are the most common cause of liver cirrhosis and cancer.
Hepatitis A and E are typically caused by ingestion of contaminated food or water. Hepatitis B, C and D usually occur as a result of parenteral contact with infected body fluids. Common modes of transmission for these viruses include receipt of contaminated blood or blood products, invasive medical procedures using contaminated equipment and for hepatitis B transmission from mother to baby at birth, from family member to child, and also by sexual contact.
Acute infection may occur with limited or no symptoms, or may include symptoms such as jaundice (yellowing of the skin and eyes), dark urine, extreme fatigue, nausea, vomiting and abdominal pain.
Scientists have identified 5 unique hepatitis viruses, identified by the letters A, B, C, D, and E. While all cause liver disease, they vary in important ways.
1) Hepatitis A virus (HAV) is present in the faeces of infected persons and is most often transmitted through consumption of contaminated water or food. Certain sex practices can also spread HAV. Infections are in many cases mild, with most people making a full recovery and remaining immune from further HAV infections. However, HAV infections can also be severe and life threatening. Most people in areas of the world with poor sanitation have been infected with this virus. Safe and effective vaccines are available to prevent HAV.
2) Hepatitis B virus (HBV) is transmitted through exposure to infective blood, semen, and other body fluids. HBV can be transmitted from infected mothers to infants at the time of birth or from family member to infant in early childhood. Transmission may also occur through transfusions of HBV-contaminated blood and blood products, contaminated injections during medical procedures, and through injection drug use. HBV also poses a risk to healthcare workers who sustain accidental needle stick injuries while caring for infected-HBV patients. Safe and effective vaccines are available to prevent HBV.
3) Hepatitis C virus (HCV) is mostly transmitted through exposure to infective blood. This may happen through transfusions of HCV-contaminated blood and blood products, contaminated injections during medical procedures, and through injection drug use. Sexual transmission is also possible, but is much less common. There is no vaccine for HCV.
4) Hepatitis D virus (HDV) infections occur only in those who are infected with HBV. The dual infection of HDV and HBV can result in a more serious disease and worse outcome. Hepatitis B vaccines provide protection from HDV infection.
5) Hepatitis E virus (HEV) is mostly transmitted through consumption of contaminated water or food. HEV is a common cause of hepatitis outbreaks in developing parts of the world and is increasingly recognized as an important cause of disease in developed countries. Safe and effective vaccines to prevent HEV infection have been developed but are not widely available.

Vaccines to immune after Hepatitis A is achieved in 99%-100% of the people by receiving two dose of inactivated virus. Vaccines to prevent Hepatitis B have been available since 1986and has been supplied into more than 177 countries. It can be achieved by having a Three-Dose recombinant virus.

World Hepatitis Day is celebrated on July 28 Every Year to celebrate awareness regarding prevention of this disease

Mumps: It is a viral disease caused by the mumps virus. Initial signs and symptoms often include fever, muscle pain, headache, and feeling tired. This is then usually followed by painful swelling of one or both parotid glands. Symptoms typically occur 16 to 18 days after exposure and resolve after 7 to 10 days. Symptoms in adults are often more severe than in children. About a third of people have mild or no symptoms. Complications may include infections of the covering of the brain (15%), pancreatitis (4%), permanent deafness, and painful testicular swelling which uncommonly results in infertility. Women may develop ovarian swelling but this does not increase the risk of infertility.
Mumps is highly contagious and spreads rapidly among people living in close quarters. The virus is transmitted by respiratory droplets or direct contact with an infected person. Only humans get and spread the disease. People are infectious to each other from a few days before the start of symptoms to four days after. After an infection a person is typically immune for life. Re-infection is possible but tends to be mild. Diagnosis is usually suspected due to parotid swelling and can be confirmed by isolating the virus on a swab of the parotid duct. Testing for IgM antibodies in the blood is simple and may be useful; however, can be falsely negative in those who have been immunized.
Mumps is preventable by two doses of the mumps vaccine. Most of the developed world includes it in their immunization programs, often in combination with measles and rubella vaccine. Countries that have low immunization rates may see an increase in cases among older age groups and thus worse outcomes. There is no specific treatment. Efforts involve controlling symptoms with pain medication such as acetaminophen. Intravenous immunoglobulin may be useful in certain complications. Hospitalization may be required if meningitis or pancreatitis develops. About one per ten thousand people who are infected die.
Without immunization about 0.1% to 1% of the population are affected per year. Widespread vaccination has resulted in a more than 90% decline in rates of disease. Mumps is more common in the developing world where vaccination is less common. Outbreaks, however, may still occur in a vaccinated population. Before the introduction of a vaccine, mumps was a common disease worldwide. Larger outbreaks of disease would typically occur every two to five years. Children between the ages of five and nine were most commonly affected. Among immunized population often those in their early 20s are affected. Around the equator it often occurs all year round while in the more northerly and Southerly regions of the world it is more common in the winter and spring. Painful swelling of the parotid glands and testicles were described by Hippocrates in the 5th century BCE.
There’s a combined Vaccine known as the MMR Vaccine which is available for Mumps, Measles and Rubella (Thus, MMR) which is widely used to prevent mumps.

Meningitis: It is an acute inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs. Meningitis can be life-threatening because of the inflammation's proximity to the brain and spinal cord; therefore, the condition is classified as a medical emergency.
The most common symptoms of meningitis are headache and neck stiffness associated with fever, confusion or altered consciousness, vomiting, and an inability to tolerate light (photophobia) or loud noises (phonophobia). Children often exhibit only non-specific symptoms, such as irritability and drowsiness. If a rash is present, it may indicate a particular cause of meningitis; for instance, meningitis caused by meningococcal bacteria may be accompanied by a characteristic rash.
A lumbar puncture diagnoses or excludes meningitis. A needle is inserted into the spinal canal to extract a sample of cerebrospinal fluid (CSF) that envelops the brain and spinal cord. The CSF is examined in a medical laboratory. The first treatment in acute meningitis consists of promptly administered antibiotics and sometimes antiviral drugs. Corticosteroids can also be used to prevent complications from excessive inflammation. Meningitis can lead to serious long-term consequences such as deafness, epilepsy, hydrocephalus and cognitive deficits, especially if not treated quickly. Some forms of meningitis (such as those associated with meningococci, Haemophilus influenzae type B, pneumococci or mumps virus infections) may be prevented by immunization. In 2013 meningitis resulted in 303,000 deaths – down from 464,000 deaths in 1990.

HIV/AIDS(Human Immunodeficiency Virus/ Acquired Immune Deficiency Syndrome): It is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV). It may also be referred to as HIV disease or HIV infection. Following initial infection, a person may experience a brief period of influenza-like illness. This is typically followed by a prolonged period without symptoms. As the infection progresses, it interferes more and more with the immune system, making the person much more susceptible to common infections, like tuberculosis, as well as opportunistic infections and tumors that do not usually affect people who have working immune systems. The late symptoms of the infection are referred to as AIDS. This stage is often complicated by an infection of the lung known as pneumocystis pneumonia, severe weight loss, skin lesions caused by Kaposi’s, or other AIDS-defining conditions.
HIV is transmitted primarily via unprotected sexual intercourse (including anal and oral sex), contaminated transfusions, hypodermic, and from mother to child during pregnancy, delivery, or breastfeeding. Some bodily fluids, such as saliva and tears, do not transmit HIV. Common methods of HIV/AIDS prevention include encouraging and practicing safe sex, needle-exchange programs, and treating those who are infected. There is no cure or vaccine; however, antiretroviral treatment can slow the course of the disease and may lead to a near-normal life expectancy. While antiretroviral treatment reduces the risk of death and complications from the disease, these medications are expensive and have side effects. Treatment is recommended as soon as the diagnosis is made. Without treatment, the average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.
Since its discovery, AIDS has caused an estimated 36 million deaths worldwide (as of 2012). In 2014 it resulted in about 1.2 million deaths and about 36.9 million people were living with HIV. HIV/AIDS is considered a pandemic—a disease outbreak which is present over a large area and is actively spreading. Genetic research indicates that HIV originated in west-central Africa during the late 19th or early 20th century. AIDS was first recognized by the United States Centers for Disease Control and Prevention(CDC) in 1981 and its cause—HIV infection—was identified in the early part of the decade.
HIV/AIDS has had a great impact on society, both as an illness and as a source of discrimination. The disease also has significant economic. There are many misconceptions about HIV/AIDS such as the belief that it can be transmitted by casual non-sexual contact. The disease has become subject to many controversies involving religion. It has attracted international medical and political attention as well as large-scale funding since it was identified in the 1980s.

Cooties: It is a fictional childhood disease, used in the United States of America and Canada as a rejection term and an infection tag game(such as Humans vs. Zombies). It is similar to the British dreaded lurgi, and to terms used in the Nordic countries, in Italy, and in New Zealand. A child is said to "catch" cooties through close contact of an "infected" person or from a person of the opposite sex of the same age. Often the "infected" person is someone who is perceived as different, such as being of the opposite sex, disabled, or shy, or who has peculiar mannerisms. Usually the phrase is used by boys, as in "now you've got girl cooties". The phrase is most commonly used by children aged 3–10; however, it may be used by children older than 10 in a cruel, sassy, or playful way.

According to Fiction, Cooties is a Sexually Transmitted Disease that is passed instantaneously when physical contact with an infected individual of the opposite sex occurs, attaching itself to your skin, the disease then spreads into your blood stream. Symptoms include ridicule, exclusion from peers and scabby encrusted sores. There is no cure for the disease, but anyone infected should find a sharp piece of metal and hammer it into his/her skull before you infect others.
Cooties are extremely deadly over time. The most common form of death is explosion that is a result of an over abundance of the cooties virus within an individual. There has been one known survivor, but the effects of the disease have caused him to be an outcast and forced him into hiding. He has been come to be known as "bigfoot".
Chicken Pox (also known as varcilla): It is a highly contagious disease caused by the initial infection with varicella zoster virus(VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab over. It usually starts on the chest, back, and face then spreads to the rest of the body. Other symptoms may include fever, feeling tired, and headaches. Symptoms usually last five to ten days. Complications may occasionally include pneumonia, inflammation of the brain, or bacterial infections of the skin among others. The disease is often more severe in adults than children. Symptoms begin ten to twenty one days after exposure to the virus.
Chickenpox is an airborne disease which spreads easily through the coughs and sneezes of an infected person. It may be spread from one to two days before the rash appears until all lesions have crusted over. It may also spread through contact with the blisters. Those with shingles may spread chickenpox to those who are not immune through contact with the blisters. The disease can usually be diagnosed based on the presenting symptom; however, in unusual cases may be confirmed by polymerase chain reaction (PCR) testing of the blister fluid or scabs. Testing for antibodies may be done to determine if a person is or is not immune. People usually only get the disease once.
The varicella vaccine has resulted in a decrease in the number of cases and complications from the disease. It protects about 70 to 90 percent of people from disease with a greater benefit for severe disease. Routine immunization of children is recommended in many countries. Immunization within three days of exposure may improve outcomes in children. Treatment of those infected may include calamine lotion to help with itching, keeping the fingernails short to decrease injury from scratching, and the use of paracetamol (acetaminophen) to help with fevers. For those at increased risk of complications antiviral medication such as aciclovi rare recommended.
Chickenpox occurs in all parts of the world. Before routine immunization the number of cases occurring each year was similar to the number of people born. Since immunization the number of infections in the United States has decreased nearly 90%. In 2013 chickenpox resulted in 7,000 deaths globally – down from 8,900 in 1990. Death occurs in about 1 per 60,000 cases. Chickenpox was not separated from smallpox until the late 19th century. In 1888 its connection to shingles was determined. The first documented use of the term chicken pox was in 1658. Various explanations have been suggested for the use of "chicken" in the name, one being the relative mildness of the disease.

Obesity: It is a medical condition in which excess body fat has accumulated to the extent that it may have a negative effect on health, leading to reduced life expectancy and/or increased health problems. In Western countries, people are considered obese when their body mass index (BMI), a measurement obtained by dividing a person's weight by the square of the person's height, is over30 kg/m2, with the range 25–30 kg/m2 defined as overweight. Some East Asian countries use stricter criteria.
Obesity increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, obstructive sleep apnea, certain types of cancer, and osteoarthritis. Obesity is most commonly caused by a combination of excessive food energy intake, lack of physical activity, and genetic susceptibility, although a few cases are caused primarily by genes, endocrine disorders, medications, or psychiatric illness. Evidence to support the view that some obese people eat little yet gain weight due to a slow metabolism is limited. On average, obese people have greater energy expenditure than their thin counterparts due to the energy required to maintain an increased body mass.
Dieting and exercising are the main treatments for obesity. Diet quality can be improved by reducing the consumption of energy-dense foods, such as those high in fat and sugars, and by increasing the intake of dietary fiber. With a suitable diet, anti-obesity drugs may be taken to reduce appetite or decrease fat absorption. If diet, exercise, and medication are not effective, a gastric balloon may assist with weight loss, or surgery may be performed to reduce stomach volume and/or bowel length, leading to feeling full earlier and a reduced ability to absorb nutrients from food.
Obesity is a leading preventable cause of death worldwide, with increasing rates in adults and children. Authorities view it as one of the most serious public health problems of the 21st century. Obesity is stigmatized in much of the modern world (particularly in the Western), though it was widely seen as a symbol of wealth and fertility at other times in history and still is in some parts of the world. In 2013, the American Medical Association classified obesity as a disease.
Smoking: It is a practice in which a substance is burned and the resulting smoke breathed in to be tasted and absorbed into the bloodstream. Most commonly the substance is the dried leaves of the tobacco plant which have been rolled into a small square of rice paper to create a small, round cylinder called a "cigarette". Smoking is primarily practiced as a route of administration for recreational drug use because the combustion of the dried plant leaves vaporizes and delivers active substances into the lungs where they are rapidly absorbed into the bloodstream and reach bodily tissue. In the case of cigarette smoking these substances are contained in a mixture of aerosol particles and gasses and include the pharmacologically active alkaloid nicotine; the vaporization creates heated aerosol and gas to form that allows inhalation and deep penetration into the lungs where absorption into the bloodstream of the active substances occurs. In some cultures, smoking is also carried out as a part of various rituals, where participants use it to help induce trance-like states that, they believe, can lead them to "spiritual enlightenment".
Cigarettes are primarily industrially manufactured but also can be hand-rolled from loose tobacco and rolling paper. Other smoking implements include pipes, cigars, bidis, hookahs, vaporizers, and bongs. Smoking-related diseases have been shown to kill approximately half of long term smokers when compared to average mortality rates faced by non-smokers. A 2007 report states that, each year, about 4.9 million people worldwide die as a result of smoking.
Smoking is one of the most common forms of recreational drug use. Tobacco smoking is the most popular form, being practiced by over one billion people globally, of whom the majority are in the developing world. Less common drugs for smoking include cannabis and opium. Some of the substances are classified as hard narcotics, like heroin, but the use of these is very limited as they are usually not commercially available.
The history of smoking can be dated to as early as 5000 BC, and has been recorded in many different cultures across the world. Early smoking evolved in association with religious ceremonies; as offerings to deities, in cleansing rituals or to allow shamans and priests to alter their minds for purposes of divination or spiritual enlightenment. After the European exploration and conquest of the Americas, the practice of smoking tobacco quickly spread to the rest of the world. In regions like India and Sub-Saharan Africa, it merged with existing practices of smoking (mostly of cannabis). In Europe, it introduced a new type of social activity and a form of drug intake which previously had been unknown.
Perception surrounding smoking has varied over time and from one place to another: holy and sinful, sophisticated and vulgar, a panacea and deadly health hazard. In the 20th century smoking came to be viewed in a decidedly negative light, especially in Western countries. This is due to smoking tobacco being among the leading causes of many diseases such as lung cancer, heart attacks, COPD, erectile dysfunction, and birth defects. The health hazards of smoking have caused many countries to institute high taxes on tobacco products, run ads to discourage use, limit ads that promote use, and provide help with quitting for those who do smoke.

Type 2 Diabetes: When you have this disease, your body does a poor job turning the carbohydrates in food into energy. This causes sugar to build up in your blood. Over time it raises your risk for heart disease, blindness, nerve and organ damage, and other serious conditions. It strikes people of all ages, and early symptoms are mild. About 1 out of 3 people with type 2 diabetes don't know they have it. 
People with type 2 diabetes often have no symptoms. When they do appear, one of the first may be being thirsty a lot. Others include dry mouth, bigger appetite, peeing a lot -- sometimes as often as every hour -- and unusual weight loss or gain. As your blood sugar levels get higher, you may have other problems like headaches, blurred vision, and fatigue. Some health habits and medical conditions related to your lifestyle can raise your odds of having type 2 diabetes, including: Smoking and Eating a lot of red meat.  Hispanics, African-Americans, Native Americans, and Asians are more likely to get it. In a healthy person, insulin helps turn food into energy. Your stomach breaks down carbohydrates into sugars. They enter the bloodstream, prompting your pancreas to release the hormone insulin in just the right amount. It helps your cells use the sugar for fuel. In type 2 diabetes, your cells can’t use sugar properly. That means there's a lot of it in your blood. If you have a condition called insulin resistance, your body makes the hormone, but your cells don’t use it or respond to it like they should. If you’ve had type 2 diabetes for a while but haven’t treated it, your pancreas will make less insulin. You can control blood sugar levels by changing your diet and losing extra weight. That will also cut your risk of complications. Carefully track the carbs in your diet. Keep amounts the same at every meal, watch how much fat and protein you eat, and cut calories. Ask your doctor to refer you to a dietician to help you make healthy choices and an eating plan. Your doctor may prescribe insulin early in your treatment and combine it with pills. It can also help people with type 2 diabetes who develop "beta-cell failure." This means the cells in your pancreas no longer make insulin when blood sugar is high. If this happens, insulin will become part of your daily routine. New drugs called non-insulin injectables are available for people with type 2 diabetes. These medications cause your body to make insulin to control blood sugar levels. If you don't treat diabetes with a healthy diet and exercise, you're more likely to get plaque in your arteries than people who don't have it. This sticky substance slows blood flow and increases your risk of clots. It leads to hardening of the arteries (called atherosclerosis), which makes you more likely to have a heart attack or stroke. About 2 of 3 people with diabetes die of heart disease. High blood sugar can damage the tiny blood vessels that bring oxygen and nutrients to the retina, a critical part of your eye. This is known as diabetic retinopathy, and it can lead to vision loss. It’s the leading cause of new cases of blindness in people between the ages of 20 and 74. Pools of blood, or hemorrhages, on the retina of an eye are visible in this image.
Historical Outbreaks to Research
Black Death: It was one of the most devastating pandemics in human history, resulting in the deaths of an estimated75 to 200 million people and peaking in Europe in the years 1346–53. Although there were several competing theories as to the aetiology of the Black Death, analysis of DNA from victims in northern and southern Europe published in 2010 and 2011 indicates that the pathogen responsible was the Yersinia pestis bacterium, probably causing several forms of plague.
The Black Death is thought to have originated in the arid plains of Central Asia, where it then travelled along the Silk Road, reaching Crimea by 1343. From there, it was most likely carried by Oriental rat fleas living on the black rats that were regular passengers on merchant ships. Spreading throughout the Mediterranean and Europe, the Black Death is estimated to have killed 30–60% of Europe's total population. In total, the plague reduced the world population from an estimated 450 million down to 350–375 million in the 14th century. The world population as a whole did not recover to pre-plague levels until the 17th century. The plague recurred occasionally in Europe until the 19th century.
The plague created a series of religious, social, and economic upheavals, which had profound effects on the course of European.
It has also got a movie based on it, which was released in 2010.
Modern treatment methods include insecticides, the use of antibiotics, and a plague vaccine. The plague bacterium could develop drug-resistance and again become a major health threat. One case of a drug-resistant form of the bacterium was found in Madagascar in 1995. A further outbreak in Madagascar was reported in November 2014.

Plague of Justinian: It was a pandemic that afflicted the Eastern Roman Empire (Byzantine Empire), especially its capital Constantinople, the Sassanid Empire, and port cities around the entire Mediterranean Sea. One of the greatest plagues in history, this devastating pandemic resulted in the deaths of an estimated 25 million (initial outbreak) to 50 million (two centuries of recurrence) people.
Recent research has confirmed that the cause of the pandemic was Yersinia pestis, the organism responsible for bubonic plague. The plague's social and cultural impact during the period of Justinian has been compared to that of the similar Black Death that devastated Europe 600 years after the last outbreak of Justinian plague. The principal historian during the 6th century, Procopius, viewed the pandemic as worldwide in scope. Genetic studies point to China as having been the primary source of the contagion.
The plague returned periodically until the 8th century.  The waves of disease had a major effect on the future course of European history. Modern historians named this plague incident after the Eastern Roman Emperor Justinian I, who was emperor at the time of the initial outbreak; he contracted the disease himself yet survived.
The number of deaths is uncertain. Modern scholars believe that the plague killed up to 5,000 people per day in Constantinople at the peak of the pandemic. The initial plague ultimately killed perhaps 40% of the city's inhabitants and caused the deaths of up to a quarter of the human population of the eastern Mediterranean. Frequent subsequent waves of the plague continued to strike throughout the 6th, 7th and 8th centuries, with the disease becoming more localized and less virulent.
This outbreak seems to have left a trace in the genome of Y. pestis itself.
After the last recurrence in 750, pandemics on the scale of Plague of Justinian did not appear again in Europe until the Black Death of the 14th century.
The Plague of Justinian is generally regarded as the first recorded instance of bubonic plague. This conclusion is based on the historical description of the clinical manifestations during the epidemic and the detection of Y. pestis DNA from human remains at ancient grave sites dated to that period. A genetic study of the bacterium causing bubonic plague based on samples taken from the remains of 14th-century plague victims in London and a survey of other samples suggests that the Plague of Justinian and others from antiquity arose from either now-extinct strains of Yersinia pestis genetically distinct from the 14th-century strain or came from pathogens entirely unrelated to bubonic plague. However, further work by the same researchers noted that the spread of several unusual modern variants of plague worldwide can be dated to an evolutionary radiation event approximately coinciding with the Plague of Justinian, supporting the notion that it was caused by a strain of bubonic plague.

Antonine Plague (Plague of Galen) :  a Greek physician living in the Roman Empire who described it—was an ancient pandemic brought back to the Roman Empire by troops returning from campaigns in the Near East. It has been suspected to have been either smallpox or measles, but the true cause remains undetermined. The epidemic may have claimed the life of Roman emperor Lucius Verus, who died in 169 and was the co-regent of Marcus Aurelius Antoninus, whose family name, Antoninus, was given to the epidemic. The disease broke out again nine years later, according to the Roman historian Dio Cassius, and caused up to 2,000 deaths a day in Rome, one quarter of those who were affected, making the disease have a mortality rate of about twenty-five percent (25%).The total deaths have been estimated at five million, and the disease killed as much as one-third of the population in some areas and devastated the Roman army.
Ancient sources agree that the epidemic appeared first during the Roman siege of Seleucia in the winter of 165–166. Ammianus Marcellinus reports that the plague spread to Gaul and the legions along the Rhine. Eutropius asserts that a large population died throughout the Empire.
In their consternation, many turned to the protection offered by magic. Lucian of Samosata's irony-laden account of the charlatan Alexander records a verse of his "which he despatched to all the nations during the pestilence... was to be seen written over doorways everywhere"—particularly in those houses which were emptied, Lucian remarks.
Plague of Athens: It was a devastating epidemic which hit the city-state of Athens in ancient Greece during the second year of the Peloponnesian War (430 BCE)when an Athenian victory still seemed within reach. It is believed to have entered Athens through Piraeus, the city's port and sole source of food and supplies. Much of the eastern Mediterranean also saw outbreak of the disease, albeit with less impact. The plague returned twice more, in 429 BC and in the winter of 427/426 BC.
Sparta and its allies, with the exception of Corinth, were almost exclusively land based powers, able to summon large land armies which were very nearly unbeatable. Under the direction of Pericles, the Athenians pursued a policy of retreat within the city walls of Athens, relying on Athenian maritime supremacy for supply while the superior Athenian navy harassed Spartan troop movements. Unfortunately the strategy also resulted in adding many people from the countryside to an already well-populated city, introducing a severe crowding factor as well as resource shortages. Due to the close quarters and poor hygiene exhibited at that time Athens became a breeding ground for disease and many citizens died including Pericles, his wife, and his sons Paralus and Xanthippus. In the history of epidemics the 'Plague' of Athens is remarkable for its one-sided affliction and bias on the ultimate outcome of a war.
In his History of the Peloponnesian War, the historian Thucydides who was present and contracted the disease himself and survived describes the epidemic. He writes of a disease coming from Ethiopia and passing through Egypt and Libya into the Greek world—a plague so severe and deadly that no one could recall anywhere it’s like, and physicians ignorant of its nature not only were helpless but themselves died the fastest, having had the most contact with the sick. In overcrowded Athens the disease killed an estimated one third to two thirds of the population. The sight of the burning funeral pyres of Athens caused the Spartans to withdraw, their troops being unwilling to risk contact with the diseased enemy. Many of Athens' infantry and expert seamen died as well as their general Pericles. After the death of Pericles, Athens was led by a succession of leaders Thucydides described as incompetent or weak. According to Thucydides, not until 415 BC had Athens recovered sufficiently to mount a major offensive, the disastrous Sicilian.
Accounts of the Athenian plague graphically describe the social consequences of an epidemic. Thucydides' account clearly details the complete disappearance of social morals during the time of the plague. The impact of disease on social and religious behaviour was also documented during the worldwide pandemic best known as the Black Death.
Cholera Outbreak of 1854: It was a severe outbreak of cholera that occurred near Broad Street in the Soho district of London, England in 1854. This outbreak is best known for the physician John Snow's study of the outbreak and his discovery that contaminated water, not air, spread cholera. This discovery came to influence public health and the construction of improved sanitation facilities beginning in the 19th century. Later, the term "focus of infection" would be used to describe places like the Broad Street pump in which conditions are good for transmission of an infection.
In the mid-19th century, the Soho district of London had a serious problem with filth due to the large influx of people and a lack of proper sanitary services: the London sewer system had not reached Soho. Many cellars (basements) had cesspools underneath their floorboards. Since the cesspools were overrunning, the London government decided to dump the waste into the River Thames. That specific action contaminated the water supply, leading to a cholera outbreak.
On 31 August 1854, after several other outbreaks had occurred elsewhere in the city, a major outbreak of cholera reached Soho. John Snow, the physician who eventually linked the outbreak to contaminated water, later called it "the most terrible outbreak of cholera which ever occurred in this kingdom."
Over the next three days, 127 people on or near Broad Street died. In the next week, three quarters of the residents had fled the area. By 10 September, 500 people had died and the mortality rate was 12.8 percent in some parts of the city. By the end of the outbreak, 616 people had died.

Great Plague of London (1665-1666): It was the last major epidemic of the bubonic plague to occur in England. It happened within the centuries-long time period of the Second Pandemic, an extended period of intermittent bubonic plague epidemics which began in Europe in 1347, the first year of the Black Death, an outbreak which included other forms such as pneumonic plague, and lasted until 1750.
The Great Plague killed an estimated 100,000 people, almost a quarter of London's population. Plague is caused by the Yersinia pestisbacterium, which is usually transmitted through the bite of an infected rat flea.
The 1664–66 epidemic was on a far smaller scale than the earlier Black Death pandemic; it was remembered afterwards as the "great" plague mainly because it was the last widespread outbreak of bubonic plague in England during the 400-year time span of the Second Pandemic.
Plague had been one of the hazards of life in Britain ever since its dramatic appearance in 1347 with the Black Death. The Bills of Mortality began to be published regularly in 1603, in which year 33,347 deaths were recorded from plague. Between then and 1665, only four years had no recorded cases. In 1563 a thousand people were reportedly dying in London each week, in 1593 there were 15,003 deaths, 1625 saw 41,313 dead, between 1640 and 1646 came 11,000 deaths, culminating in 3,597 for 1647. The 1625 outbreak was recorded at the time as the 'Great Plague', until 1665 surpassed it. These official figures are likely to under-report actual numbers.
By late autumn, the death toll in London and the suburbs began to slow until, in February 1666, it was considered safe enough for the King and his entourage to come back to the city. With the return of the monarch, others began to return: The gentry returned in their carriages accompanied by carts piled high with their belongings. The judges moved back from Windsor to sit in Westminster Hall, although Parliament, which had been prorogued in April 1665, did not reconvene until September 1666. Trade recommenced and businesses and workshops opened up. London was the goal of a new wave of people who flocked to the city in expectation of making their fortunes. Writing at the end of March 1666, Lord Clarendon, the Lord Chancellor, stated "... the streets were as full, the Exchange as much crowded, the people in all places as numerous as they had ever been seen ...".
The plague in London largely affected the poor, as the rich were able to leave the city by either retiring to their country estates or residing with kin in other parts of the country. The subsequent Great Fire of London, however, ruined many city merchants and property owners. As a result of these events, London was largely rebuilt and Parliament enacted the Rebuilding of London Act 1666. Although the street plan of the capital remained relatively unchanged, some improvements were made: streets were widened, pavements were created, open sewers abolished, wooden buildings and overhanging gables forbidden, and the design and construction of buildings controlled. The use of brick or stone was mandatory and many gracious buildings were constructed. Not only was the capital rejuvenated, but it became a healthier environment in which to live. Londoners had a greater sense of community after they had overcome the great adversities of 1665 and 1666.

Ebola Outbreak of 2015: The most widespread epidemic of Ebola virus disease (commonly known as "Ebola") in history is currently ongoing in West Africa, and has caused significant loss of life in the West African nations of Liberia, Guinea and Sierra Leone, with minor outbreaks elsewhere. It has caused significant mortality, with reported case fatality rates of up to 70% and specifically 57–59% among hospitalized patients. Ebola virus disease was first described in 1976 in two simultaneous outbreaks in Sudan and Democratic Republic of the Congo; this is the 26th outbreak in history and the first to occur in the West African subcontinent. The outbreak began in Guinea in December 2013 and then spread to Liberia and Sierra Leone. A small outbreak of twenty cases occurred in Nigeria and one case occurred in Senegal. Several cases were reported in Mali, and an isolated case occurred in the United Kingdom and another in Sardinia. Imported cases in the United States and Spain led to secondary infections of medical workers but did not spread further. As of 30 December 2015, the World Health Organization (WHO) and respective governments have reported a total of 28,638 suspected cases and 11,315 deaths, though the WHO believes that this substantially understates the magnitude of the outbreak.
This is the first Ebola outbreak to reach epidemic proportions; past outbreaks were brought under control within a few weeks. Extreme poverty, a dysfunctional healthcare system, a mistrust of government officials after years of armed conflict, and the delay in responding to the outbreak for several months have all contributed to the failure to control the epidemic. Other factors include local burial customs that include washing of the body after death and the spread to densely populated cities. As the disease progressed, many hospitals, short on both staff and supplies, became overwhelmed and closed, leading some health experts to state that the inability to treat other medical needs may have been causing "an additional death toll [that is] likely to exceed that of the outbreak itself". Hospital workers, who work closely with the highly contagious body fluids of the diseased, have been especially vulnerable to catching the disease. In August 2014, the WHO reported that ten percent of the dead had been healthcare workers. In September 2014, it was estimated that the countries' capacity for treating Ebola patients was insufficient by the equivalent of 2,122 beds; by December there were a sufficient number of beds to treat and isolate all reported Ebola cases, although the uneven distribution of cases was resulting in serious shortfalls in some areas. On 28 January 2015, the WHO reported that for the first time since the week ending 29 June 2014, there had been fewer than 100 new confirmed cases reported in a week in the three most-affected countries. The response to the epidemic then moved to a second phase, as the focus shifted from slowing transmission to ending the epidemic. On 8 April 2015, the WHO reported a total of only 30 confirmed cases, and the weekly update for 29 July reported only seven new cases. On 7 October 2015, all three of the most seriously affected countries recorded their first joint week without any new cases, however, as of late 2015, while the large-scale epidemic had ended, sporadic new cases were still continuing to emerge, frustrating hopes that the epidemic can be declared over.
On 8 August 2014, the World Health Organization declared the outbreak a public health emergency of international concern. The WHO has been widely criticised for its delay in taking action to address the epidemic. By September 2014, Médecins Sans Frontières/Doctors Without Borders (MSF), the non-governmental organization (NGO) with the largest working presence in the affected countries, had grown increasingly critical of the international response. Speaking on 3 September, the president of MSF spoke out concerning the lack of assistance from the United Nations member countries saying, "Six months into the worst Ebola epidemic in history, the world is losing the battle to contain it."  In a 26 September statement, the WHO said, "The Ebola epidemic ravaging parts of West Africa is the most severe acute public health emergency seen in modern times" and the Director-General, Margaret Chan, called the outbreak "the largest, most complex and most severe we've ever seen”. In March 2015, the United Nations Development Group reported that due to a decrease in trade, closing of borders, flight cancellations, and foreign investment and tourism activity fuelled by stigma, the epidemic has resulted in vast economic consequences in both the affected areas and even throughout African nations that experienced low or no cases of Ebola.
On 31 July 2015, the WHO announced "an extremely promising development" in the search for an effective vaccine for Ebola disease. While the vaccine up to now shows 100% efficacy in individuals, more conclusive evidence is needed on its capacity to protect populations through what is called herd immunity.
In August 2015, after substantial progress in reducing the scale of the epidemic, the WHO held a meeting to work out a "Comprehensive Care Plan for Ebola Survivors" and identify research needed to optimize clinical care and social well-being. Saying "the Ebola outbreak has decimated families, health systems, economies, and social structures", the WHO called the aftermath "an emergency within an emergency." Of special concern is recent research that shows some Ebola survivors experience so-called Post-Ebola Syndrome, with symptoms so severe that survivors may require medical care for months and even years. As the epidemic was coming to an end in December 2015, the United Nations announced that 22,000 children had been orphaned, losing one or both parents to Ebola.
Cocoliztli Epidemic: It refers to millions of deaths in the territory of New Spain in present-day Mexico in 16th century attributed to one or more illnesses collectively called cocoliztli.
The cause of the epidemic remains unknown though it might have been an indigenous viral hemorrhagic fever, perhaps exacerbated by the worst droughts to affect that region in 500 years and living conditions for indigenous peoples of Mexico in the wake of European invasion.  Some historians have suggested it was typhus, measles, or smallpox, though the symptoms did not match.
Cocoliztli epidemics usually occurred within two years of a major drought while another disease called "matlazahuatl" had appeared within two years of the rainy season. The epidemic in 1576 happening after a drought stretching from Venezuela to Canada. The correlation between the drought and the disease seems to be that in the rains that followed the drought, populations of the Vesper mouse, a carrier of viral hemorrhagic fever, increased as conditions improved. There have been 12 epidemics since thought to be of cocoliztli, with the largest being in 1545, 1576, 1736, and 1813.
According to Francisco Hernandez, a physician who witnessed the outbreak in 1576, symptoms included high fever, severe headache, vertigo, black tongue, dark urine, dysentery, severe abdominal and thoracic pain, head and neck nodules, neurologic disorders, jaundice, and profuse bleeding from the nose, eyes, and mouth; death frequently occurred in 3 to 4 days.
Cocoliztli is often said to be the bug to the invention of Ebola.

The First Cholera Pandemic: It began near Calcutta and spread throughout Southeast Asia to the Middle East, eastern Africa and the Mediterranean coast. While cholera had spread across India many times previously, this outbreak went further; it reached as far as China and the Mediterranean Sea before receding. Hundreds of thousands of people died as a result of this pandemic, including many British soldiers, which attracted European attention. This was the first of several cholera pandemics to sweep through Asia and Europe during the 19th and 20th centuries. This first pandemic spread over an unprecedented range of territory, affecting almost every country in Asia.
Cholera was endemic to the lower Ganges River. At festival times, pilgrims frequently contracted the disease there and carried it back to other parts of India on their returns, where it would spread, then subside. The first cholera pandemic started similarly, as an outbreak that was suspected to have begun in 1817 in the town of Jessore. Some epidemiologists and medical historians have suggested that it spread globally through a Hindu pilgrimage, the Kumbh Mela, on the upper Ganges River. Earlier outbreaks of cholera had occurred near Purnia in Bihar, but scholars think these were independent events. In 1817, cholera began spreading outside the Ganges delta. By September 1817, the disease had reached Calcutta on the Bay of Bengal and quickly spread to the rest of the subcontinent. By 1818 the disease broke out in Bombay, on the west coast.
In March 1820 the disease was identified in Siam, in May 1820 it had spread as far as Bangkok and Manila, in spring of 1821 it reached Java, Oman, and Anhai in China; in 1822 it was found in Japan, in the Persian Gulf, in Baghdad, in Syria, and in the Transcaucacus; and in 1823 cholera reached Astrakhan, Zanzibar, and Mauritius.
In 1824, transmission of the disease ended. Some researchers believe that may have been due to the cold winter of 1823–24, which would have killed the bacteria in the water supplies.
The movement of British Army and Navy personnel is believed to have contributed to the range of the pandemic. Hindu pilgrims carried cholera within the subcontinent, as had happened many times previously, but British troops carried it overland to Nepal and Afghanistan. The Navy and merchant ships carried people with the disease to the shores of the Indian Ocean, from Africa to Indonesia, and north to China and Japan.
The total deaths from the epidemic remain unknown. Scholars of particular areas have estimated death tolls. For instance, some estimate that Bangkok might have suffered 30,000 deaths from the disease. In Semarang, Java 1,225 people died in eleven days in April 1821.
Second Cholera Pandemic: It was a cholera pandemic that reached from India across western Asia to Europe, Great Britain and the Americas, as well as east to China and Japan. Cholera caused more deaths, more quickly, than any other epidemic disease in the 19th century. It is exclusively a human disease, and it can spread through many means of travel, such as by persons via caravan, ship, and airplanes. Cholera is known most popularly to spread through warm fecal-contaminated river waters and contaminated foods. The causative microorganisms (Cholera vibrio) flourish by reaching humans. It is treatable with oral re-hydration therapy and preventable with adequate sanitation and water treatment.
Historians believe that the first pandemic had lingered in Indonesia and the Philippines in 1830. Although not much is known about the journey of the cholera pandemic in east India, many believe that this pandemic began, like the first, with outbreaks along the Ganges River delta in India. From there the disease spread along trade routes to cover most of India. By 1828 the disease had traveled to China. Cholera was also reported in China in 1826 and 1835, and in Japan in 1831. In 1829, Iran was apparently infected with cholera from Afghanistan. It spread during the Moscow invasion in August 1830. By 1831 the epidemic had infiltrated Russia’s main cities and towns. Russian soldiers brought the disease to Poland in February 1831. There were a reported 250,000 cases of cholera in Russia and 100,000 deaths.

The Third Pandemic: It is the designation of a major bubonic plague pandemic that began in Yunnan province in China in 1855. This episode of bubonic plague spread to all inhabited continents, and ultimately killed more than 12 million people in India and China alone. According to the World Health Organization, the pandemic was considered active until 1959, when worldwide casualties dropped to 200 per year.
The name refers to this pandemic being the third major bubonic plague outbreak known to western sources. The first was the Plague of Justinian, which ravaged the Byzantine Empire and surrounding areas from 541 to 542. The second was the Black Death, which killed at least one third of Europe's population in a series of expanding waves of infection from 1346 to 1353.
Casualty patterns indicate that waves of this late-19th-century/early-20th-century pandemic may have been from two different sources. The first was primarily bubonic and was carried around the world through ocean-going trade, through transporting infected persons, rats, and cargoes harboring fleas. The second, more virulent strain was primarily pneumonic in character with a strong person-to-person contagion. This strain was largely confined to Asia, in particular Manchuria and Mongolia.
The initial outbreak occurred in Yunnan Province in south-western China in the 1850s.The disease was stable within the province, but was spread due to the Panthay Rebellion. The rebellion displaced local tribes, and also changed animal harvesting practices, leading to greater contact with infected animals. In addition, the rebellion meant that refugees from the conflict moved south, into regions of China with larger populations.
Plague came to British India in 1896, most likely from Hong Kong where the epidemic had been festering since 1894. Over the next thirty years, the country would lose 12.5 million people to the disease. Almost all cases were bubonic, with only a very small percentage changing to pneumonic plague. (Orent, p. 185) The disease was initially seen in port cities, beginning with Bombay (now Mumbai), but later emerged in Pune, Kolkata, and Karachi (now in Pakistan). By 1899, the outbreak spread to smaller communities and rural areas in many regions of India. Overall, the impact of plague epidemics was greatest in western and northern India—in the provinces then designated as Bombay, Punjab, and the United Provinces—while eastern and southern India were not as badly affected.
Researchers working in Asia during the "Third Pandemic" identified plague vectors and the plague bacillus. In 1894, in Hong Kong, Swiss-born French bacteriologist Alexandre Yersin isolated the responsible bacterium (Yersinia pestis) and determined the common mode of transmission. Japanese physician and researcher Kitasato Shibasaburō initially misidentified the bacterium. In 1898, French researcher Paul-Louis Simond demonstrated the role of fleas as a vector.

1918 Spanish Flu Pandemic:  It was an unusually deadly influenza pandemic, the first of the two pandemics involving H1N1 influenza virus. It infected 500 million people across the world, including remote Pacific islands and the Arctic, and resulted in the deaths of 50 to 100 million (three to five percent of the world's population), making it one of the deadliest natural disasters in human history.
Most influenza outbreaks disproportionately kill juvenile, elderly, or already weakened patients; in contrast, the 1918 pandemic predominantly killed previously healthy young adults. Modern research, using virus taken from the bodies of frozen victims, has concluded that the virus kills through a cytokine storm (overreaction of the body's immune system). The strong immune reactions of young adults ravaged the body, whereas the weaker immune systems of children and middle-aged adults resulted in fewer deaths among those groups.
Historical and epidemiological data are inadequate to identify the pandemic's geographic origin. It was implicated in the outbreak of encephalitis lethargica in the 1920s.
To maintain morale, wartime censors minimized early reports of illness and mortality in Germany, Britain, France, and the United States; but papers were free to report the epidemic's effects in neutral Spain (such as the grave illness of King Alfonso XIII), creating a false impression of Spain as especially hard hit—thus the pandemic's nickname Spanish flu. In Spain, a different nickname was adopted, the Naples Soldier (Soldado de Nápoles), which came from a musical operetta (zarzuela) titled La canción del olvido (The Song of Forgetting), which premiered in Madrid during the first epidemic wave. Federico Romero, one of the librettists, quipped that the play's most popular musical number, Naples Soldier, was as catchy as the flu.

Avian Bird Flu of 1957: It refers to an illness caused by any of many different strains of influenza viruses that have adapted to a specific host. All known viruses that cause influenza in birds belong to the species influenza A virus. All subtypes (but not all strains of all subtypes) of influenza A virus are adapted to birds, which is why for many purposes avian flu virus is the influenza A virus. (Note, however, that the "A" does not stand for "avian").
Adaptation is not exclusive. Being adapted toward a particular species does not preclude adaptations, or partial adaptations, toward infecting different species. In this way, strains of influenza viruses are adapted to multiple species, though may be preferential toward a particular host. For example, viruses responsible for influenza pandemics are adapted to both humans and birds. Recent influenza research into the genes of the Spanish flu virus shows it to have genes adapted to both birds and humans, with more of its genes from birds than less deadly later pandemic strains.
While its most highly pathogenic strain (H5N1) had been spreading throughout Asia since 2003, avian influenza reached Europe in 2005, and the Middle East, as well as Africa, the following year.= On January 22, 2012, China reported its second human death due to bird flu in a month following other fatalities in Vietnam and Cambodia. Companion birds in captivity and parrots are highly unlikely to contract the virus, and there has been no report of a companion bird with avian influenza since 2003. Pigeons do not contract or spread the virus. 84% of affected bird populations are composed of chicken and farm birds, while the 15% is made up of wild birds according to capture-and-release operations in the 2000s, during the SARs pandemic. The first deadly Canadian case was confirmed on January 3, 2014. On December 2, 2014, two turkey farms in British Columbia, Canada, had been placed under quarantine after the Canadian Food Inspection Agency confirmed an avian flu outbreak.
H2N2 is a subtype of the influenza A virus. H2N2 has mutated into various strains including the Asian flu strain (now extinct in the wild), H3N2, and various strains found in birds. It is also suspected of causing a human pandemic in 1889. The geographic spreading of the 1889 Russian flu have been studied and published.
Some researchers have asserted that the 1889–1890 flu pandemic (also known as Russian flu) was caused by the influenza virus A virus subtype H2N2. More recent research has suggested H3N8 as a more likely cause. It is the earliest flu pandemic for which detailed records are available. "The 1889 pandemic, known as the Russian Flu, began in Russia and spread rapidly throughout Europe. It reached North America in December 1889 and spread to Latin America and Asia in February 1890. About 1 million people died in this pandemic."
The category 2 Asian flu pandemic outbreak of influenza A virus originated in China in early 1956, and lasted until 1958. Some authors believe it originated from a mutation in wild ducks combining with a pre-existing human strain. Other authors are less certain. The virus was first identified in Guizhou. It spread to Singapore in February 1957, reached Hong Kong by April, and the US by June. The death toll in the US was about 69,800. Estimates of worldwide deaths caused by this pandemic varies widely depending on source, ranging from one to four million, with WHO settling on "about two million".

H1N1: It is the subtype of influenza A virus that was the most common cause of human influenza (flu) in 2009, and is associated with the 1918 outbreak known as the Spanish Flu.
It is an orthomyxovirus (The family of RNA viruses to which H1N1 belongs) that contains the glycoproteins haemagglutinin and neuraminidase. For this reason, they are described as H1N1, H1N2 etc. depending on the type of H or N antigens they express with metabolic synergy. Haemagglutinin causes red blood cells to clump together and binds the virus to the infected cell. Neuraminidase are a type of glycoside hydrolase enzyme which help to move the virus particles through the infected cell and assist in budding from the host cells.
Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza. H1N1 strains caused a small percentage of all human flu infections in 2004–2005.  Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza).
In June 2009, the World Health Organization (WHO) declared the new strain of swine-origin H1N1 as a pandemic. This strain is often called swine flu by the public media. This novel virus spread worldwide and had caused about 17,000 deaths by the start of 2010. On August 10, 2010, the World Health Organization declared the H1N1 influenza pandemic over, saying worldwide flu activity had returned to typical seasonal patterns.
It is in most cases known as Swine Flu, Which has been causing many Outbreaks, Including those in 2009 and 2015 (India).

SARS and MERS in the 21st Century: The severe acute respiratory syndrome outbreak in 2002 and 2003 led to more than 8,000 infections worldwide and killed close to 10% of those infected.
It was caused by a corona virus that made a species jump from bats to humans through the intermediate host of farmed civet cats bred for human consumption in China. From recognition of the outbreak to identification of the agent and animal reservoir, to containment and resolution, the outbreak occurred during a 9-month period.
 we are now in the 18th month of the Middle East respiratory syndrome (MERS) outbreak. It is of interest at this point to evaluate the current status of the outbreak, which is far from being contained or, for that matter, from being understood in terms of the epidemiology. Perhaps because there have been fewer than 200 cases of MERS, with fewer than 100 deaths, and very limited spread outside of the Arabian Peninsula has something to do with it. Add to that the observation that severe disease has been seen primarily in older individuals with comorbidities, whereas, in contrast to severe acute respiratory syndrome (SARS), young, healthy individuals tend to have asymptomatic-to-mild disease. Clearly, the threat level to the world is perceived as much less with MERS than it was with SARS.
Because SARS started and spread in China, which has formidable scientific expertise, and then spread to Western countries with their scientific resources may explain the differences in response to and knowledge about the MERS and SARS epidemics. There seems to be a large discrepancy between the worldwide scientific resources thrown into the SARS outbreak, which seem to dwarf the resources applied to the MERS outbreak. This could be a result of limited scientific resources in the countries primarily involved, as well as the fact that SARS spread to “the backyards” of industrialized nations while MERS has not. Alternatively, perhaps the novelty of a coronavirus that was lethal for humans in the case of SARS attracted more attention of scientists and funding than the second-place MERS. Regardless of the explanation, the result is that we clearly know less about MERS than we did about SARS, despite the much longer duration of the MERS outbreak.
We know that the novel coronaviruses responsible for both SARS and MERS probably originated in bats and then spread to an intermediate mammalian host from which humans were infected. The discovery of civet cats as an infection source of SARS for humans occurred about 4 months after the international recognition that there was an outbreak of a new disease. In contrast, it was not until 10 months after the recognition of MERS that camels were suspected as the possible intermediate host.
From the experience thus far, it seems likely that the MERS outbreak will continue to limp along with sporadic cases occurring primarily in the Arabian Peninsula followed by nosocomial outbreaks when first introduced into a health care facility. This may change when the routes of transmission to the sporadic cases are clearly identified, or if there is a change in the virus leading to the super spreader phenomenon observed with SARS or a change in virulence of the virus. Without definitive identification of the non-human animal reservoir, there is unlikely to be a practical approach to stopping the epidemic.
Even if camels are proven to be the animal reservoir, an approach to containment will be difficult without a vaccine. Unlike the civet cat in China, camels are important to the daily lives and economies of the countries in the Middle East and elimination of camels is unlikely to occur.
Initial symptoms are flu-like and may include fever, myalgia, lethargy symptoms, cough, sore throat, and other nonspecific symptoms.

Terms to Learn
Endemic: It is used to refer to any infection which is maintained in a population without the need of external inputs.  For example, chickenpox is endemic (steady state) in the UK, but malaria is not. Every year, there are a few cases of malaria reported in the UK, but these do not lead to sustained transmission in the population due to the lack of a suitable vector.
Outbreak: It is a sudden increase in occurrences of a disease in a particular time and place. It may affect a small and localized group or impact upon thousands of people across an entire continent. Two linked cases of a rare infectious disease may be sufficient to constitute an outbreak. Outbreaks may also refer to epidemics, which affect a region in a country or a group of countries, or pandemics, which describe global disease outbreaks.
Pathogenicity: It refers to the ability of an organism to cause disease (ie, harm the host). This ability represents a genetic component of the pathogen and the overt damage done to the host is a property of the host-pathogen interactions. Commensals and opportunistic pathogens lack this inherent ability to cause disease.
Triage:  It is the process of determining the priority of patients' treatments based on the severity of their condition. This rations patient treatment efficiently when resources are insufficient for all to be treated immediately. The term comes from the French verb trier, meaning to separate, sift or select.
The term triage may have originated during the Napoleonic Wars from the work of Dominique Jean Larrey. The term was used further during World War I by French doctors treating the battlefield wounded at the aid stations behind the front. 
Prevalence: It is the proportion of a population found to have a condition (typically a disease or a risk factor such as smoking or seat-belt use). It is arrived at by comparing the number of people found to have the condition with the total number of people studied, and is usually expressed as a fraction, as a percentage or as the number of cases per 10,000 or 100,000 people.
Incidence: It is a measure of the probability of occurrence of a given medical condition in a population within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.
Retrovirus: It is a virus that is composed not of DNA but of RNA. Retroviruses have an enzyme, called reverse transcriptase that gives them the unique property of transcribing their RNA into DNA after entering a cell. The retroviral DNA can then integrate into the chromosomal DNA of the host cell, to be expressed there. HIV is a retrovirus.
Incubation: It is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent. In a typical infectious disease, incubation period signifies the period taken by the multiplying organism to reach a threshold necessary to produce symptoms in the host.
Infectious vs. Lifestyle Diseases:
Infectious Disease
Lifestyle Disease
An infectious disease is a sickness you can catch (or give to) other people.
Lifestyle diseases are sicknesses you cannot get or give to other people. You get lifestyle diseases from unhealthy lifestyle (little exercise, too much unhealthy food, etc.). 
 The flu and chicken pox are examples of infectious diseases.
Examples of lifestyle diseases are type two diabetes and gout.

Epidemiological Transition: It is a phase of development witnessed by a sudden and stark increase in population growth rates brought about by medical innovation in disease or sickness therapy and treatment, followed by a re-levelling of population growth from subsequent declines in fertility rates. "Epidemiological transition" accounts for the replacement of infectious diseases by chronic diseases over time due to expanded public health and sanitation. This theory was originally posited by Abdel Omran in 1971
Intervention: It is an orchestrated attempt by one or many people – usually family and friends – to get someone to seek professional help with an addiction or some kind of traumatic or crisis, or other serious problem. The term intervention is most often used when the traumatic event involves addiction to drugs or other items. Intervention can also refer to the act of using a similar technique within a therapy session.
Descriptive Epidemiology vs. Analytic Epidemiology:
Descriptive Epidemiology
Analytic Epidemiology
It deals with the frequency and the distribution of risk factors in populations and enables to assess the extent of a disease. It can thus provide hypotheses of etiologic research.
It aims to research and study risk and protector factors of diseases.

Risk Factors: is a variable associated with an increased risk of disease or infection. Sometimes, determinant is also used, being a variable associated with either increased or decreased risk.
Cohort:  It is a group of subjects who have shared a particular event together during a particular time span (e.g., people born in Europe between 1918 and 1939; survivors of an aircrash; truck drivers who smoked between age 30 and 40). The people who would’ve together survived through the Black Death, SARS and MERS are also examples.
Zoonosis: These are infectious diseases of animals (usually vertebrates), that can naturally be transmitted to humans.
Fomite: It is any object or substance capable of carrying infectious organisms, such as germs or parasites, and hence transferring them from one individual to another. Skin cells, hair, clothing, and bedding are common hospital sources of contamination.
Latency: It is the time between exposure to a pathogen, chemical or radiation, and when symptoms first become apparent.
Outlier: It is an observation point that is distant from other observations. An outlier may be due to variability in the measurement or it may indicate experimental error; the latter are sometimes excluded from the data set.
Independent vs. Dependent Variables:
Independent Variables
Dependent Variables
It is exactly what it sounds like. It is a variable that stands alone and isn't changed by the other variables you are trying to measure. For example, someone's age might be an independent variable. Other factors (such as what they eat, how much they go to school, how much television they watch) aren't going to change a person's age. In fact, when you are looking for some kind of relationship between variables you are trying to see if the independent variable causes some kind of change in the other variables, or dependent variables.
  Just like an independent variable, a dependent variable is exactly what it sounds like. It is something that depends on other factors. For example, a test score could be a dependent variable because it could change depending on several factors such as how much you studied, how much sleep you got the night before you took the test, or even how hungry you were when you took it. Usually when you are looking for a relationship between two things you are trying to find out what makes the dependent variable change the way it does.
Many people have trouble remembering which is the independent variable and which is the dependent variable. An easy way to remember is to insert the names of the two variables you are using in this sentence in they way that makes the most sense. Then you can figure out which is the independent variable and which is the dependent variable:
(Independent variable) causes a change in (Dependent Variable) and it isn't possible that (Dependent Variable) could cause a change in (Independent Variable).

False Negative(s): It is a test result that indicates a person does not have a disease or condition when the person actually does have it, according to the National Institute of Health (NIH). False negative test results can occur in many different medical tests, from tests for pregnancy , tuberculosis or Lyme disease to tests for the presence of drugs or alcohol in the body.
Double Blind Trials: It is a trial where neither the researchers nor the patients know what they are getting. The computer gives each patient a code number. And the code numbers are then allocated to the treatment groups. Your treatment arrives with your code number on it. Neither you nor your doctor knows whether it is the new treatment or not.
The list of patients and their code numbers is kept secret until the end of the trial. In an emergency the researchers could find out which trial group a patient was in, but generally no one knows until the trial had finished.
Agent: Something that causes some disease/illness to happen.
Patient Zero: It is the initial patient in the population of an epidemiological investigation, or more generally, the first case of a condition or syndrome (not necessarily contagious) to be described in the medical literature, whether or not the patient is thought to be the first person affected.
Chain of Infection:  It is a chain which is made up of six different links: pathogen (infectious agent), reservoir, portal of exit, means of transmission, portal of entry, and the new host. Each link has a unique role in the chain, and each can be interrupted, or broken, through various means.
The first link is the pathogen itself. This is the disease-causing organism. For many illnesses and diseases this is a virus or bacterium. In order to break this link, various methods can be used, including the pasteurization of milk, the chlorination of drinking water, or the use of disinfectants.
The second link is the reservoir. This is the natural environment that the pathogen requires for survival. Reservoirs can be a person, an animal, or an environmental component, such as soil or water. This link can be broken through medical treatment and testing, insect and rodent eradication, or quarantine.
The third link is the portal of exit. This link is needed for the pathogen to leave the reservoir. If the reservoir is a human, then the portal of exit may be saliva, mucous membranes, feces, blood, or nose or throat discharges. By using barrier methods, such as condoms or masks, or covering the mouth while coughing, this link can be broken.
The fourth link is the means of transmission. The pathogen can be transmitted either directly or indirectly. Direct transmission requires close association with the infected host but not necessarily physical contact. Indirect transmission requires a vector, such as an animal or insect. The link can be broken through hand washing, safe sex practices, or avoiding contact with infected individuals.
Link number five is the portal of entry. Entry of the pathogen can take place in one of three ways: penetration, inhalation, or ingestion. The level and severity of an infection may depend on the depth of penetration. Similar to the portal of exit, barrier methods, such as condoms or masks, can be used to break this link along with other methods, such as insect repellents.
The final link is the new host, Once in the new host, various factors influence the severity of infection, including the strength of the immune system and the reproductive rate of the pathogen. Immunization, health promotion, and medical treatment can be used to break this link in the chain.
Droplet Spread: It is used to refer to the direct dissemination of a pathogen from the reservoir to a susceptible host’s conjunctiva, nose or mouth- by spray with relatively large, short-ranged  aerosols produced by sneezing, coughing or talking.
Herd Immunity: It is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune. In a population in which a large number of individuals are immune, chains of infection are likely to be disrupted, which stops or slows the spread of disease. The greater the proportion of individuals in a community who are immune, the smaller the probability that those who are not immune will come into contact with an infectious individual.
Morbidity: It comes from the word morbid, which means "or of relating to disease," like the number of cases of any disease in an areas —morbidity rates for polio that plummeted in the 20th century.
Co-morbidity: It is the presence of one or more additional disorders (or diseases) co-occurring with a primary disease or disorder; or the effect of such additional disorders or diseases. The additional disorder may also be a behavioral or mental disorder.
Infant Mortality: It is the death of a child less than one year of age. It is measured as infant mortality rate (IMR), which is the number of deaths of children under one year of age per 1000 live births.
The leading causes of infant mortality are birth asphyxia, pneumonia, pre-term birth complications, neonatal infection, diarrhoea, malaria, measles and malnutrition. Many factors contribute to infant mortality such as the mother's level of education, environmental conditions, and political and medical infrastructure. Improving sanitation, access to clean drinking water, immunization against infectious diseases, and other public health measures could help reduce high rates of infant mortality.
Child mortality is the death of a child before the child's fifth birthday, measures as the Under-5 Child Mortality Rate (U5MR). National statistics sometimes group these two mortality rates together. Globally, ten million infants and children die each year before their fifth birthday; 99% of these deaths occur in developing nations. Infant mortality takes away society's potential physical, social, and human capital.
The infant mortality rate is one of three indicators used to monitor achievements towards the Fourth Goal of the eight Millennium Development Goals. This goal's target value is to "Reduce by two-thirds, between 1990 and 2015, the under-five mortality rate".

Heterozygote Advantage:  It is the case in which the heterozygote genotype has a higher relative fitness than either the homozygote dominant or homozygote recessive genotype. The specific case of heterozygote advantage due to a single locus is known as overdominance. In more general terms, overdominance is a condition in genetics where the phenotype of the heterozygote lies outside of the phenotypical range of both homozygote parents, and heterozygous individuals have a higher fitness than homozygous individuals.
Polymorphism can be maintained by selection favoring the heterozygote, and this mechanism is used to explain the occurrence of some kinds of genetic variability. A common example is the case where the heterozygote conveys both advantages and disadvantages, while both homozygotes convey a disadvantage. A well-established case of heterozygote advantage is that of the gene involved in sickle cell anaemia.
Centre for Disease Control: It is the leading national public health institute of the United States. The CDC is a federal agency under the Department of Health and Human Services and is headquartered in unincorporated DeKalb County, Georgia, a few miles northeast of the Atlanta city limits.
Its main goal is to protect public health and safety through the control and prevention of disease, injury, and disability. The CDC focuses national attention on developing and applying disease control and prevention. It especially focuses its attention on infectious disease, food borne pathogens, environmental health, occupational safety and health, health promotion, injury prevention and educational activities designed to improve the health of United States citizens. In addition, the CDC researches and provides information on non-infectious diseases such as obesity and diabetes and is a founding member of the International Association of National Public Health Institutes.

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