"Bushmeat," despite its name, is not President George W. Bush's favorite food.
Throughout the dense forests of central Africa, bushmeat is eaten primarily by a primate called mangabey. In the monkey house at the zoo, the sign on its cage reads: "Sooty Mangabey monkey (Cercocebus). Habitat: Rain forests of Equatorial West Africa, especially in the Cameroons, Guinea and Gabon. It lives mainly on leaves, seeds and bugs, and is preyed upon by leopards, lions, hyenas and wild dogs."
Homo sapiens also prey on the primate species. Ape meat commands premium prices in upscale eateries all over central Africa. Sooty mangabeys are hunted not only for what's sold as bushmeat, but also as pets. The hunters who track and butcher them in the wild, without benefit of sanitary inspection, risk catching the viral infections carried by the blood of their prey - namely the HIV pathogen.
Molecular epidemiologist Nathan Wolfe, at Johns Hopkins University in Baltimore, explained where primates fit into the equation. "Mangabeys harbor the human HIV-2 strain; chimpanzees [Pan troglodytes] HIV-1," he said. "The hunting and butchering of wild monkeys, gorillas and apes infected with SIV [simian immunodeficiency virus] is thought to have triggered the human AIDS pandemic some 20 years ago." An article in a recent The Lancet carries the title: "Naturally acquired simian retrovirus infections in central African hunters." Wolfe is the lead author.
"Our findings," Wolfe observed, "consist of zoonotic infections with simian foamy virus [SFV], a variant retrovirus endemic in most Old World primates. In a survey of the Cameroons, we found that 10 individuals of 1,099 [1 percent] in the population had antibodies in their blood - reflecting SFV infection.
"In the 20 years since its discovery, HIV-1 has caused morbidity and mortality in man on a previously unimaginable scale. We demonstrated first of all that HIV was not just a single virus; it's multiple foamy viruses. There's HIV-1 and HIV-2, each of which came from a different non-human primate.
"When we first discovered these foamy retroviruses [FRV] in monkeys - simians - we used electron microscopy [EM]," Wolfe said. "Foaminess is not unique to primates. Some non-primates have also been discovered. We could see that when we grew these viruses up in cell culture in the laboratory, they killed cells. And in that process we could see a foamy appearance in the EM.
"To avoid contamination," Wolfe went on, "we processed human and primate samples separately in laboratories in different buildings. We examined 200 individuals from each of nine villages in southern Cameroon, close to natural non-human primate habitats, both forested and non-forested. Each of the three people who tested positive by PCR were from a different rural village in the lowland forest of southern Cameroon - a region of high primate biodiversity.
"Of the three, the first FRV-infected person was a 45-year-old man. He had butchered and consumed monkey, chimpanzee and gorilla meat and hunted all these groups, using at various times guns, bows and wire snares. The second FRV-infected person was a 48-year-old woman who said that she consumed and butchered monkeys and hunted them with wire snares The third infected participant was a 25-year-old man who butchered monkeys and chimpanzees, but who may also have been exposed through contact with a pet monkey."
Demand For Primate Meat Plus Open Forest Access
"FRV infections in this study were from several geographically isolated locations," Wolfe recounted, "suggesting that - contrary to conventional wisdom - retrovirus zoonosis is widespread. It arises in various locations where people are naturally exposed to non-human primates. The scarce information that exists suggests," he went on, "that there is no secondary transmission or morbidity and mortality in people with SFV infection. The increased amount of it in central Africa has resulted from a combination of urban demand for bushmeat and greater access to primate habitats provided by logging roads, which increased the frequency of human exposure to primate retroviruses and other disease-causing agents."
An accompanying commentary in the same March 20, 2004, issue of The Lancet bears the title: "Cross-species transmissions of simian retroviruses in Africa and risk for human health." It starts off: "Emerging zoonotic diseases are among the most important public health threats threatening humanity. One of the major examples is the AIDS epidemic, which emerged in the 1980s to human beings several decades earlier."
The commentary's author, Martine Peeters from the Research Institute for Development in Montpellier, France, stated: "For foamy viruses no disease has yet been observed in human beings," but she added that "it cannot be excluded that the pathogenicity of foamy viruses with a particular simian strain might emerge in the human population after a long incubation period, and especially as life expectancy increases."
Dead-End Transmission Or Clusters Of Human Spread?
"Studies will now need to be started," Peeters ventured, "to examine whether in these natural settings in Africa human-to-human transmission occurs with foamy viruses, and whether any disease is associated with these infections. Such epidemiological surveys in rural African populations will show whether the [simian] human foamy virus infections described in Cameroon are isolated dead-end cross-species transmissions.
"Commercial logging is an important economic activity in west-central Africa," Peeters pointed out, "and has led to road construction into remote forest areas, human migration and the development of social and economic networks (including those of sex workers), which support this industry. We recently found a high prevalence of HIV among young women in a logging area in Cameroon, suggesting human [AIDS] infection with simian retroviruses (which have a long incubation period), might spread unrecognized for several years and lead to another AIDS epidemic."
"As to our ongoing work," Wolfe said, "we're asking: Do these foamy viruses cause disease? We don't know if they do or not. Do they spread from person to person? We don't know that either. We're focusing on that right now."