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PATHOGENIC THREATS TO GORILLA CONSERVATION

Like every organism, gorillas are threatened by pathogens and parasites, some of them species specific, some shared by other species. Paradoxically, populations that are hunted for Bushmeat seem less prone to Ebola outbreaks, whereas ape populations at the highest densities (and therefore the target of conservation attention) are at greatest risk of an epidemic. Dramatic declines in several ape populations are attributed to outbreaks of ebola haemorrhagic fever, and efforts are under way to develop a method of vaccinating ape populations at risk.

The close phylogenetic relationship between humans and great apes creates exceptionally high potential for pathogen exchange. This has resulted in disease emergence in humans as an unintentional affect of the hunting and butchering of the African great apes, responsible for human outbreaks of Ebola and the global AIDS pandemic (Hahn et al., 2000; Le- roy et al., 2004; Plantier et al., 2009), as well as high rates of mortality in wild chimpanzee (Pan troglodytes) populations associated with anthropozoonotic transmission of human re- spiratory viruses (Köndgen et al., 2008; Kaur et al., 2008). In addition to such cases where pathogenic agents responsible for epidemics could be confirmed, epidemics of a polio-like etiology in chimpanzees (Goodall 1986) and measles-like eti- ology in mountain gorillas (Ferber 2000) are also suspected to have been of human origin.

Less visible than epidemics of acute disease, but equally impor- tant as risk factors for ape conservation are chronic pathogens, which can compromise host immune function and reduce re- productive capacity. Proximity between wild apes and people has been demonstrated to promote transmission of the common gas- trointestinal bacterium Escherichia coli. Moreover, gorillas and chimpanzees living in proximity to humans have been shown to harbor E. coli resistant to multiple antibiotics used by people in the region, indicating that microbes or their genes can ‘‘diffuse’’ from humans to great apes even in the best of conservation cir- cumstances (Goldberg et al., 2007; Rwego et al., 2008). These studies stress that direct contact between species is not neces- sary for interspecific disease transmission. Indeed, most trans- mission of gastrointestinal pathogens between people, livestock,

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and wild apes is probably indirect and environmental. Pathogens such as Cryptosporidium, Giardia, and enteric bacteria (i.e., Shi- gella, Salmonella, E. coli, etc.) readily contaminate water and soil and may persist in wet areas (Gillespie et al., 2008).

These demonstrations of various human pathogens negative- ly impacting wild apes has sparked considerable debate con- cerning the costs and benefits to surviving ape populations of scientific research, ecotourism, and current conservation and management paradigms (summarized in a special issue of the American Journal of Primatology, Garber 2008). Despite the disease-related risks, the consensus is that both research and tourism have contributed in overwhelmingly positive ways to the conservation of gorillas and other apes, enhancing their long-term survival by increasing their scientific and economic value, respectively. Nevertheless, such activities as well as over- lap in great ape and human habitat may have unintended con- sequences on the health and survival of wild ape populations.

In August 2009, more than 80 experts from 17 countries rep- resenting field and laboratory researchers, wildlife veterinar- ians, virologists, and conservation biologists came together in Entebbe, Uganda for a Great Ape Health Workshop to develop best practice guidelines for great ape health. Consensus was that “minimum preventative standards” should be required for all people entering great ape habitat, for tourism, research, or any other reason. Since the majority of observed diseases in great apes of possible or proven human origin are respiratory diseases, the primary measures proposed were wearing masks in proximity to apes, maintaining a minimum of 7 meters dis- tance, a zero tolerance policy on visibly ill people visiting apes, disinfection of hands and boots before visiting apes, and proof of vaccination for all visitors. Further measures may be site specific and more complex. Another important point discussed was the importance of community health programs to lower infection risks from outside protected areas and to provide ben- efits for people living in proximity to great ape habitat. Guide- lines evolved from this consensus process will be published by IUCN within the best practices for ape conservation series (Leendertz 2010).

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