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Emerging diseases may change their frequency gradually over time, or they may experience sudden epidemic growth. The importance of vigilance was made clear during the Ebola hemorrhagic fever epidemic in western Africa through 2014–2015. Although health experts had been aware of the Ebola virus since the 1970s, an outbreak on such a large scale had never happened before ( [link] ). Previous human epidemics had been small, isolated, and contained. Indeed, the gorilla and chimpanzee populations of western Africa had suffered far worse from Ebola than the human population. The pattern of small isolated human epidemics changed in 2014. Its high transmission rate, coupled with cultural practices for treatment of the dead and perhaps its emergence in an urban setting, caused the disease to spread rapidly, and thousands of people died. The international public health community responded with a large emergency effort to treat patients and contain the epidemic.

Emerging diseases are found in all countries, both developed and developing ( [link] ). Some nations are better equipped to deal with them. National and international public health agencies watch for epidemics like the Ebola outbreak in developing countries because those countries rarely have the health-care infrastructure and expertise to deal with large outbreaks effectively. Even with the support of international agencies, the systems in western Africa struggled to identify and care for the sick and control spread. In addition to the altruistic goal of saving lives and assisting nations lacking in resources, the global nature of transportation means that an outbreak anywhere can spread quickly to every corner of the planet. Managing an epidemic in one location—its source—is far easier than fighting it on many fronts.

Ebola is not the only disease that needs to be monitored in the global environment. In 2015, WHO set priorities on several emerging diseases that had a high probability of causing epidemics and that were poorly understood (and thus urgently required research and development efforts).

A reemerging infectious disease is a disease that is increasing in frequency after a previous period of decline. Its reemergence may be a result of changing conditions or old prevention regimes that are no longer working. Examples of such diseases are drug-resistant forms of tuberculosis , bacterial pneumonia , and malaria . Drug-resistant strains of the bacteria causing gonorrhea and syphilis are also becoming more widespread, raising concerns of untreatable infections.

Graph of Known human cases of Ebola virus diseases worldwide from 1976 – 2015. There were 604 in 1976-77. There were 44 in 1978-79. There were 0 from 1980 – 87. There were 3 in 1988-89. There were 4 in 1990-91. There were 368 in 1994-95. There were 100 in 1996-97. There were 0 in 1998-99. There were 547 in 2000-2001. There were 178 in 2002-2003. There were 18 in 2004-2005. There were 413 in 2006-2007. There were 38 in 2006-2007. There were 38 in 2008-2009. There was 1 in 2010-2011. There were 53 in 2012-2013. There were 28,718 in 2014-2015.
Even before the Ebola epidemic of 2014–15, Ebola was considered an emerging disease because of several smaller outbreaks between the mid-1990s and 2000s.
Some Emerging and Reemerging Infectious Diseases
Disease Pathogen Year Discovered Affected Regions Transmission
AIDS HIV 1981 Worldwide Contact with infected body fluids
Chikungunya fever Chikungunya virus 1952 Africa, Asia, India; spreading to Europe and the Americas Mosquito-borne
Ebola virus disease Ebola virus 1976 Central and Western Africa Contact with infected body fluids
H1N1 Influenza (swine flu) H1N1 virus 2009 Worldwide Droplet transmission
Lyme disease Borrelia burgdorferi bacterium 1981 Northern hemisphere From mammal reservoirs to humans by tick vectors
West Nile virus disease West Nile virus 1937 Africa, Australia, Canada to Venezuela, Europe, Middle East, Western Asia Mosquito-borne

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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