THE HIV virus has jumped from primates to people on at least seven separate occasions in recent history, not twice as is commonly thought. And people in Cameroon are showing up with symptoms of HIV, but are testing negative for both the virus and its primate equivalent SIV, the virus from which HIV is thought to have evolved. That suggests that new strains of an HIV-like virus are circulating in wild animals and infecting people who eat them, sparking fears that such strains could fuel an already disastrous global HIV pandemic.
The warnings come from experts who gathered this week for the annual meeting of the Society for Conservation Biology at Columbia University, New York. They say that deforestation and the trade in bush meat are creating the ideal conditions for new diseases to emerge, as people have ever closer contact with exotic animals that harbour novel pathogens. 鈥淓xisting viruses might sometimes recombine into more drug-resistant forms. Such a virus could show up at new locations in deadlier incarnations,鈥� says Tonie Rocke, an epidemiologist with the US Geological Survey.
The conference reports follow the discovery this year that simian foamy virus, another disease that infects monkeys, has been found in bush-meat hunters and three different species of primates. As yet, it hasn鈥檛 caused ill-effects, but it could mutate into something more insidious. 鈥淏asically, this is a virus looking for a disease,鈥� says William Karesh, director of the World Conservation Society鈥檚 field veterinary programme.
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Despite those concerns, we still do not have a clear idea of how many wild animals are killed and eaten, David Wilkie, co-chair of the Wildlife Conservation Society, told the conference. He has carried out the first-ever survey of daily bush-meat consumption by rural communities in Gabon. Over two years, he documented a flourishing, but previously unrecognised, informal trade in bush meat, where rural communities hunted and ate small game, having already caught most available primates. He thinks official studies of bush meat sold in markets account for only 40 per cent of the total bush meat eaten in the country.
鈥淚n the Congo basin alone, between 1 and 5 million metric tonnes of bush meat was consumed last year,鈥� says Heather Eves, head of the Bushmeat Crisis Task Force (BCTF), a non-governmental organisation that monitors the trade. And the dangers of eating such animals are real. The BCTF points out that SIV infection has now been reported in 26 different species of African nonhuman primates, many of which are hunted and sold as food.
The bush-meat trade is not the only way new diseases could jump into humans. The trade in wildlife, both for agriculture and as pets, is a major global business estimated to be worth billions of dollars. In 2002 alone, for instance, over 38,000 mammals, 365,000 birds, 2 million reptiles, 49 million amphibians, and 216 million fish were imported into the US. Last year, monkeypox jumped from pet prairie dogs to their human masters. That 鈥渨as just a gentle wake-up call,鈥� says Rocke. Previously the disease had only been known to infect humans after bush-meat hunters ate red colobus monkeys.
The trade in exotic farmed meat also appears to have sparked an unusual outbreak of a common human parasite called Trichinella. This year, a farmed crocodile in Papua New Guinea was discovered with Trichinella, which was only thought to infect mammals, after being fed wild pig meat (Emerging Infectious Diseases, vol 10, p 1507). In 1999, another farmed crocodile in Zimbabwe was similarly infected. 鈥淭here is a strong chance that infected crocodiles may be in other countries, and could infect humans who eat them,鈥� says Edoardo Pozio, a parasitologist at Rome鈥檚 institute of public health. People in Papua New Guinea who eat crocodile meat have already been found to have the parasite, which can cause fever, rashes, and respiratory and neurological problems in humans.
Rocke says there are few safeguards to prevent the spread of diseases through the wildlife trade, and is calling for stricter import and quarantine restrictions.