Eradication of infectious diseases

Eradication is the reduction of an infectious disease's prevalence in the global host population to zero. It is sometimes confused with elimination, which describes either the reduction of an infectious disease's prevalence in a regional population to zero, or the reduction of the global prevalence to a negligible amount. Further confusion arises from the use of the term eradication to refer to the total removal of a given pathogen from an individual (also known as clearance of an infection), particularly in the context of HIV and certain other viruses where such cures are sought. Selection of infectious diseases for eradication is based on rigorous criteria, as both biological and technical features determine whether a pathogenic organism is (at least potentially) eradicable. The targeted organism must not have a non-human reservoir (or, in the case of animal diseases, the infection reservoir must be an easily identifiable species, as in the case of rinderpest), and/or amplify in the environment. This implies that sufficient information on the life cycle and transmission dynamics is available at the time an eradication initiative is programmed. An efficient and practical intervention (such as a vaccine or antibiotic) must be available to interrupt transmission of the infective agent. Studies of measles in the pre-vaccination era led to the concept of the critical community size, the size of the population below which a pathogen ceases to circulate. Use of vaccination programmes before the introduction of an eradication campaign can reduce the susceptible population. The disease to be eradicated should be clearly identifiable, and an accurate diagnostic tool should exist. Economic considerations, as well as societal and political support and commitment, are other crucial factors that determine eradication feasibility. Two infectious diseases have successfully been eradicated: smallpox and rinderpest. There are also four ongoing programs, targeting poliomyelitis, yaws, dracunculiasis, and malaria. Five more infectious diseases have been identified as of April 2008 as potentially eradicable with current technology by the Carter Center International Task Force for Disease Eradication—measles, mumps, rubella, lymphatic filariasis and cysticercosis. So far, two diseases have been successfully eradicated—one specifically affecting humans (smallpox), and one affecting a wide range of ruminants (rinderpest). Smallpox was the first disease, and so far the only infectious disease of humans, to be eradicated by deliberate intervention. It became the first disease for which there was an effective vaccine in 1798 when Edward Jenner showed the protective effect of inoculation (vaccination) of humans with material from cowpox lesions. Smallpox (variola) occurred in two clinical varieties: variola major, with a mortality rate of up to 40 percent, and variola minor, also known as alastrim, with a mortality rate less than one percent. The last naturally occurring case of Variola major was diagnosed in October 1975 in Bangladesh. The last naturally occurring case of smallpox (Variola minor) was diagnosed on 26 October 1977, on Ali Maow Maalin, in the Merca District, of Somalia. The source of this case was a known outbreak in the nearby district of Kurtuware. All 211 contacts were traced, revaccinated, and kept under surveillance. After two years' detailed analysis of national records the global eradication of smallpox was certified by an international commission of smallpox clinicians and medical scientists on 9 December 1979, and endorsed by the General Assembly of the World Health Organization on 8 May 1980. However, there is an ongoing controversy regarding the continued storage of the smallpox virus by labs in the US and Russia, as any accidental or deliberate release could create a new epidemic for persons born after or in the late 1980s due to the cessation of vaccinations against the smallpox virus. During the 20th century, there were a series of campaigns to eradicate rinderpest, a viral disease which infected cattle and other ruminants and belonged to the same family as measles, primarily through the use of a live attenuated vaccine. The final, successful campaign was led by the Food and Agriculture Organization of the United Nations. On 14 October 2010, with no diagnoses for nine years, the Food and Agriculture Organization announced that the disease had been completely eradicated, making this the first (and so far the only) disease of livestock to have been eradicated by human undertakings.