In this photo-gallery epidemics, epidemic outbreaks, their occurence, the causing pathogenes and their vectors are introduced.
Epidemic (of a disease) affecting many persons at the same time, and spreading from person to person in a locality where the disease is not permanently prevalent.
Epidemic occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience.
Epidemiologists often consider the term outbreak to be synonymous to epidemic, but the general public typically perceives outbreaks to be more local and less serious than epidemics.
Epidemics of infectious disease are generally caused by a change in the ecology of the host population (e.g. increased stress or increase in the density of a vector species), a genetic change in the parasite population or the introduction of a new parasite to a host population (by movement of parasites or hosts). Generally, an epidemic occurs when host immunity to a parasite population is suddenly reduced below that found in the endemic equilibrium and the transmission threshold is exceeded.
An epidemic may be restricted to one location; however, if it spreads to other countries or continents and affects a substantial number of people, it may be termed a pandemic. The declaration of an epidemic usually requires a good understanding of a baseline rate of incidence; epidemics for certain diseases, such as influenza, are defined as reaching some defined increase in incidence above this baselineA few cases of a very rare disease may be classified as an epidemic, while many cases of a common disease (such as the common cold) would not.
The historically ocurring top 10 epidemics are the following:
- The Black Death
- The Plague of Justinian
- The 1918-19 Influenza Pandemic
- The Third Plague Pandemic
- The 1916 Polio Epidemic
- The First Cholera Pandemic
- The Plague of Athens
- India's Smallpox Epidemic
- Memphis Yellow Fever
- SARS
- bubonic plague
- Chikungunya virus
- cholera
- dengue fiver
- ebola
- hand, foot and mouth diseases
- hepatitis B
- HIV/AIDS
- influenza
- malaria
- measles
- meningitis
- mumps
- plaque
- SARS coronavirus
- small pocks
- yellow fever
The WHO's Twelfth General Programme of Work sets the reduction of "mortality, morbidity and societal disruption resulting from epidemics... through prevention, preparedness, response and recovery activities" as one its five strategic imperatives.
WHO maintaines the Global Outbreak Alert and Response Network (GOARN), a technical collaboration of existing institutions and networks who pool human and technical resources for the rapid identification, confirmation and response to outbreaks of international importance. The Network provides an operational framework to link this expertise and skill to keep the international community constantly alert to the threat of outbreaks and ready to respond.