Origins of HIV and the AIDS Epidemic

September 11-12, 2000, The Royal Society, London, United Kingdom

Jonathan Weber, FRCP, FRCPath, FmedSci, Keith Alcorn, Medical Writer

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In This Article

Be a Virus, See the World

The meeting opened with an overview of cross-species infections, given by Professor Albert Osterhaus of Erasmus University, Rotterdam, The Netherlands. He noted that new pathogens are constantly emerging from animal reservoirs to challenge animal and human populations. Of these, HIV is undoubtedly the most famous zoonosis of the latter half of the 20th century, although the Spanish influenza epidemic of 1918-1919 claimed more human lives than all the conflicts of the 20th century combined. Osterhaus showed that cross-species epidemics are an annual event. The decimation of North Sea seals by a canine paramyxovirus and the appearance of related viruses in dolphins and porpoises are recent examples. All human infectious diseases ultimately have an animal origin, and natural transfer of these infections is a common event in animal populations. Human transfers are seen regularly with influenza A, an avian virus initially, transferred to humans generally through pigs. However, the recent Hong Kong chicken influenza outbreak in humans showed that the threat posed by zoonotic viruses is ever-present, and continuous vigilance will be required.

Dr. Kevin de Cock of the Centers for Disease Control and Prevention, Atlanta, Georgia, gave a rigorous overview of the epidemiological principles that should underlie any discussion of the origins of HIV. He described how The River proposes an ecologic association between contaminated OPV and the emergence of HIV and noted that the hypothesis relies on data that carry with them a high degree of bias and chance in their assembly. For example, on the basis of 38 cases of AIDS identified in the medical literature before 1980 and 58 HIV-1 isolates from stored serum samples, Hooper posits an association between OPV vaccination sites and the earliest manifestation of AIDS. However, these sources are inevitably subject to selection bias, as these cases had unusual characteristics, which caused them to come to the attention of subsequent investigators. Much valuable sera was destroyed in Kinshasa during the 1980s, for example, and Kevin de Cock pointed out that case reports in the medical literature are predominantly the product of academic medical centers, most likely to be accessed by Europeans. In addition, the AIDS cases identified by Hooper and other historians, such as the assiduous Mirko Grmek, lack confirmatory serologic data in most cases. OPV and early AIDS cases might be noncausally associated due to other confounding factors, such as proximity to major transport routes.

De Cock also criticized attempts to analyze SIV distribution among chimpanzees in Central Africa as epidemiologically irrelevant to understanding what took place in the past, just as current HIV prevalence tells us nothing about the date of HIV's emergence in a population. While Kinshasa has yielded evidence of HIV infection as far back as 1959, prevalence has remained stable at around 6% in pregnant women for the past decade, whereas HIV prevalence has climbed to considerably higher levels in southern Africa despite much later introduction of HIV. De Cock argued that the interplay of risk factors is a key determinant in the evolution of the HIV epidemic in a specific locale: male circumcision, history of genital herpes, and female sexual debut before the age of 16 were factors significantly associated with a higher HIV prevalence in a comparative prevalence study of 4 cities in Cameroon, East Africa, and southern Africa.

Dr. Leopold Zekeng of the Cameroon Laboratoire de Sante Hygiene Mobile reviewed HIV and SIV infections in Cameroon and the theory that monkey-hunting Pygmy tribes in the region might have been the vectors for the transfer of HIV from chimps to the wider population. Although Cameroon provides the richest diversity of HIV groups in the world, playing host to infections with HIV-1 groups M, N and O, the more recently identified groups are very rare, with a stable prevalence of HIV-1 group O (2% to 3%) and only 5 identified cases of group N infection among 6500 individuals sampled. Within group M, subtype A and A/G recombinants are predominant. Zekeng and colleagues investigated HIV prevalence among 2 Pygmy tribes and found that it was lower than among the predominant Bantu and strongly associated with contact with urban centers, suggesting that the theory that Pygmy hunters have acted as a bridge for HIV into the human population is probably unfounded.

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