Dispatches

As long as man has hunted wild animals, says William Karesh (Wildlife Conservation Society, Bronx, NY), people have caught diseases from carcasses. But as the commercialization of tropical forests has increased over the past century, people are coming into close contact with once isolated animal species. As a result, warns Beatrice Hahn (University of Alabama at Birmingham, GA), we are now being exposed to potentially dangerous new infectious agents as never before. AIDS is a good example of how forest commercialization can disastrously affect human health. The emergence of HIV1 in Africa in the early 20th century coincided with a period of massive human intervention in the forest, explains Rebecca Hardin (McGill University, Montreal). “Between 1900 and 1950, there was the rubber boom, the initiation of logging, and considerable road and railroad construction”, she says. “Local people had always eaten bushmeat, often as a delicacy, but [at that time] the forests became laced with hunters and their camps, all there to provide meat for migrant laborers.” At some point during this period, says Hahn, simian immunodeficiency viruses (SIVs) moved into humans – probably through exposure to infected blood during bushmeat preparation. HIV1’s closest SIV relative is found in chimpanzees and, as Hahn and her collaborators recently reported (Science 2003; 300: 1713), this virus may itself be the result of recombination between two SIVs acquired by chimpanzees from monkey meat. Both Hahn and Hardin warn that, with the recent commercialization and expansion of the bushmeat trade, other SIVs may also jump to humans. To find out how likely this is, Hahn is developing assays to screen a large archive of monkey sera for SIVs. “If infection rates are high in the wild and we constantly come into contact with these monkeys”, she explains, “then the risk of transmission to people will also be high”, although exposure will not necessarily result in a new human disease. People can also contract the Ebola virus from wild animals. However, although non-human primates get Ebola – indeed, the current Congo outbreak was detected in great apes in November, 2 months before the first human cases – the identity of the true reservoir species remains unknown. “People can get Ebola directly from this mystery reservoir or by handling another infected animal or person”, explains Karesh. People could therefore contract Ebola by handling any meat caught in the bush, in this case probably during subsistance rather than commercial hunting. Another recent example of how human diseases can originate in wild meat comes from SARS. Peter Ben Embarek (World Health Organization) explains that a coronavirus similar to that found in SARS patients has been isolated from masked palm civets and raccoon dogs being sold as delicacies in animal markets in Guangdong, China. “We also know that some of the original cases were people who handled wild animals or food in markets or restaurants”, he continues. “However, we do not know yet whether the true SARS reservoir is either of these species, the badger ferret, in which we discovered viral antibodies, or another animal.” Wild meat consumption constitutes a substantial risk to human health, concludes Ben Embarek, and the danger is increased as people move into relatively undisturbed forests, where they are exposed to new infectious agents. To minimize the threat, Ben Embarek calls for such moves to be done in an organized way, with minimal disruption of the local ecology. “Conservation and environmental protection are important”, he says, “not only to save biodiversity, but also to protect ourselves from close contact with species that harbor dangerous infectious agents”. “There is a clear link between the health of great apes and people”, adds Karesh. At the same time as he and his colleagues are training officials in central Africa to monitor the health of great apes, they are also pushing to improve the health of the local people. Vaccination of villagers against childhood diseases such as measles protects both the people and the gorillas, he points out. Furthermore, by explaining to local people how they can get diseases from animals, the researchers have been able to reduce the consumption of primates. Hardin sees initiatives such as that headed by Karesh as important for both human health and conservation. But, she says, international stakeholders also need to be convinced that it would be wise to put off large-scale exploitation of certain forest regions until infectious agents are more thoroughly researched. “The leadership of influential people is key to building local skills for adequate surveillance and monitoring, if we are to use forests without causing either extinctions or the transmission of new and deadly diseases to the human population”, she concludes. Dispatches