Bushmeat in Africa as a Potential Threat to People's Health

Infectious diseases, which have been transmitted from animals to humans, constitute a major part of the catastrophic disease epidemics of modern times. The best-known example of this is AIDS, which has confronted humanity with one of the greatest health problems in history. In 2003, UNAIDS published statistics indicating that 3 million people had already died of AIDS. Africa south of the Sahara remains the centre of the AIDS epidemic and the damage done to the various countries' economies is enormous.
AIDS broke out at the start of the 1980s. It is a consequence of the transmission of the simian immunodeficiency virus (SIV) from primates to people, which probably took place several decades earlier. Based on genome and phylogenetic relationships, two AIDS viruses have been distinguished: HIV-1 and HIV-2. HIV-1 can be traced back to SIVcpz found in the central African chimpanzee; HIV-2 originated in SIVsm found in West African mangabeys (Barre-Sinoussi et al. 1983; Clavel et al. 1986). Because of the affinity of virus strains there seems to be no doubt that the virus has been transmitted from manga-beys to humans at least six times, independently of each other, whereas the virus was transmitted from chimpanzees to humans only once. HIV-2 infections seem to be restricted to West Africa, whereas HIV-1 has developed into a global threat.
But it is not only SIV that has infected humans via primates. The so-called HTLVs (human T-lymphotrophic viruses type 1 and 2) have their origins in STLV (simian T-lymphotrophic virus). In addition, Wolfe et al. (2004) recently reported that another retrovirus (i.e. a virus that carries RNA as its genetic information), the primate foamy virus, has been transmitted to the human population. Each primate foamy virus infection was contracted from a distinct lineage of the virus, involving cross-species transmissions from three different primate species.
The three virus groups share a common trait in that they don't have a pathogenic effect on their primary hosts, but cause symptoms of disease in their new host. However, while HIV-1 infections have spread globally, HIV-2 remains restricted to West Africa, whereas HTLV is most prevalent in tropical Africa. In contrast to HIV, only some carriers of the HTLV virus actually develop the disease - and this only after a long incubation period. To date, very little is known about the primate foamy virus and there is as yet no indication that the virus can be transmitted from humans to humans.
Pathogens that can cause acute disease symptoms also have great significance. Among them are the viruses that cause monkey smallpox and Ebola, which can kill non-human primates as well as humans. The Ebola virus caused havoc among gorillas and chimpanzees in Gabon and the Congo Republic and killed a major part of these populations; this is probably the most dangerous example of the threat it presents (Walsh et al. 2003; Leroy et al. 2004). It is probably responsible for the current dramatic decrease of gorillas in the Odzala National Park (press release by the International Primatological Society).
Contact with blood and body fluids, for example during hunting and cutting up of the animal prey, can lead to disease transmission. This is considered a primary mechanism of HIV transmission. The widespread African custom of keeping primates as pets also increases the risk of infection. By now, more than 30 primate species are known to be infected with SIV. Some of the SIV strains have already been transmitted from one primate species to another, which suggests that they could be transmitted to humans sooner or later (Peeters et al. 2002). This risk has been increasing at a constant rate ever since more stakeholders have become involved in the bushmeat trade. Animals have always been hunted in Africa, but not at current levels. There are many reasons for the increase in hunting and the bushmeat trade. Firstly, the well-to-do classes of the cities are willing to pay considerably more for bush-meat than for the meat of domesticated animals. Hence the demand increases. In addition, new roads, particularly logging roads, are opening rainforest areas that were formerly virtually inaccessible. Modern weapons make hunting easier and, at the same time, increase the pressure on the hunters, as they can pay for new guns and ammunition only if they bring down a sufficient quantity of prey. Lastly, many rainforest areas have accommodated migrants from climatically less favoured areas of Africa. These migrants do not obey local hunting taboos.
For all these reasons, the restriction of hunting activities is increasingly important - not only for the protection of many endangered primate species, but also to reduce the risk of disease transmission to humans.

Johannes Refisch

References
Barre-Sinoussi, F. et al. (1983) Isolation of a T-lymphotropic retrovirus from a patient at risk for acquired immunodeficiency syndrome (AIDS). Science 220, 868-871
Clavel, F. et al. (1986) Molecular cloning and polymorphism of the human immune deficiency virus type 2. Nature 324, 691-695
Leroy, E. M. et al. (2004) Multiple Ebola virus transmission events and rapid decline of central African wildlife. Science. 303, 387-390
Peeters M. et al. (2002) A plethora of simian immunodeficiency viruses in primate bush-meat: expanding bushmeat trade may pose new risks to human health. Emerging Infectious Diseases 8, 451-457
Walsh, P. D. et al. (2003) Catastrophic ape decline in western equatorial Africa. Nature 422, 611-614
Wolfe, N. D. et al. (2004) Naturally acquired simian retrovirus infections in Central African hunters. The Lancet 363, 932-937

Dr. Johannes Refisch studied the effect of poaching on monkeys in the Taï Forest, Côte d’Ivoire, and is co-director of the Taï Monkey Project. Now he is developing a project on SIV in monkeys for the Schweizerisches Tropeninstitut.

Gorillas in general - overview

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