Pandemics, Origins of

The Origin of HIV

In 1980, the same year the World Health Organization formally announced a major victory in the global eradication of smallpox, the first patients who developed a new and unusual type of pneumonia were being diagnosed. This marked the beginning of one of the most devastating infectious diseases in history, the HIV/AIDS pandemic. Approximately 2.7 million new HIV infections were estimated to have occurred in 2007 alone, corresponding to one person becoming infected every 10 seconds. In some African countries, the pandemic is thought to have decreased average life expectancy by approximately 15 years.

The origin of HIV has long been debated. Two strains are known, HIV-1, which is the predominant virus worldwide, and HIV-2. The oldest known HIV-1 infection was identified in a sample collected in 1959 from a Bantu male living in the Democratic Republic of Congo. Humans are not the natural host of the virus. Where did the virus come from, and how did it cross into the human species? There is now evidence supporting the view that HIV emerged from simian immunodeficiency viruses, which are retroviruses that naturally infect many different nonhuman primates in Africa, from which they were introduced into the human population on several different occasions. HIV-1 emerged after a virus infecting a particular chimpanzee subspecies, Pan troglodytes troglodytes, crossed into humans; and HIV-2 is thought to have originated from a similar virus that crossed from sooty mang-abeys. Both species are commonly hunted and sold at markets as “bushmeat,” and some of these animals are kept as pets. One hypothesis proposes that close contact with pets, contact with blood or blood products during hunting and butchering, [Page 560]and the consumption of improperly cooked infected meat all facilitated the transmission of these viruses to humans.

HIV is not the only retrovirus originating in animals. Cross-species transmission has more recently become apparent for another pathogen, the human T-cell leukemia virus (HTLV), which is estimated to infect approximately 20 million people worldwide. While the majority of individuals infected with HTLV remain without symptoms, approximately 1% to 4% of those infected with HTLV-1, the most studied type, develop a form of T-cell leukemia or lymphoma over the course of 20 to 30 years, and others develop a progressive degenerative condition of the nervous system. Several studies that examined bushmeat hunters from central Africa revealed that contact with blood and body fluids during hunting of nonhu-man primates provides an ideal opportunity for the cross-species transmission of HTLV and facilitates the infection of humans.

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