The influence of individual, group, and anthropogenic factors on gastrointestinal parasite infections in baboons of the Cape Peninsula, South Africa.
Summary of project
Human activities have caused substantial and potentially irreversible changes to nonhuman primate habitats over the last century (Chapman & Peres 2001). The Cape Peninsula in South Africa is a classic example of this phenomenon, with urban sprawl and agriculture posing a serious threat to the continued survival of the local chacma baboon (Papio ursinus) population. Anthropogenic changes to the habitat may lead to health issues in wildlife that are still poorly understood, such as the alteration of parasite transmission rates, host range, and virulence (Daszak et al. 2000; Patz et al. 2000). This is one of the reasons why parasitic infections have been identified as a critical component to consider in conservation biology (May 1988; Scott 1988). However, little is known about factors that influence the host range of parasites in natural populations (Pedersen et al. 2005) and it is currently unclear what aspects of anthropogenic changes to the physical environment facilitate the transmission of infectious agents among wild nonhuman primates or between nonhuman primates and humans. It is therefore important to understand how patterns of parasitism in wild hosts are influenced by host-intrinsic factors, (e.g., ranging patterns, group size, host density, intraspecific and interspecific contact rates, and diet), and environmental factors (e. g. climate, vegetation type). In addition, increased contact between human and non-human primates increases the possibility of parasite transmission in both directions and of sharing infectious diseases (Appleton 1989; Chapman et al. 2005).
In order to establish how parasite infection dynamics are being affected by both natural and anthropogenic factors in the baboon population of the Cape Peninsula, this study had four major goals:
- To determine the gastrointestinal parasite diversity and prevalence of the chacma baboon population of the Cape Peninsula, South Africa. To compare these data with those obtained for other baboon populations within South Africa and other baboon species, in various localities across the African continent.
- To explore the influence of host-intrinsic individual factors (e.g., age, sex, reproductive status, and social status) on parasite species richness (PSR), prevalence, and egg/larval output./li>
- To investigate potential anthropogenic influences on parasite infection dynamics by comparing parasite data collected for six baboon troops subjected to varying levels of human interaction and anthropogenically transformed land.
- To examine the potential for cross-transmission of helminths between baboons and humans by comparing the genetics of specific parasites with a high prevalence in both humans and baboons living within the Cape Peninsula (e.g., Trichuris spp.).
Data on parasite diversity and prevalence were obtained from 616 faecal samples collected from over 350 individuals in eight troops (six from the Cape Peninsula, one from Pringle Bay, and one from Wildcliff Nature Reserve) between July 2006 and August 2007. Faeces were processed using a modified formalin-ether sedimentation technique and helminth eggs and protozoan cysts were identified. A series of potential host-intrinsic (e.g., host sex and age) and host-extrinsic (e.g., troop characteristics, climate) determinants of host-parasite dynamics were investigated. For the molecular analyses of the nematode Trichuris sp., the ITS1-5.8S rDNA-ITS2 region was amplified by PCR from DNA extracted from Trichuris nematodes dissected from the guts of individual baboons from different Cape Peninsula troops. The amplified ITS1-5.8S rDNA-ITS2 regions were sequenced and compared to the ITS1-5.8S rDNA-ITS2 region of Trichuris sp. obtained from human patients.
ResultsThe helminth and protozoan fauna of the Cape Peninsula baboon population was similar to both neighbouring and geographically disparate chacma baboon populations in South Africa. Distribution of helminth infection within a troop was influenced by the age of the host but not by other individual-level traits (i.e., gender and female reproductive and social status). Protozoan and helminth species richness was highest in the troop (Kanonkop) with the least human contact and the most pristine indigenous vegetation and was lowest in the troop (Tokai) with the highest levels of anthropogenic disturbance. Prevalences of the nematodes Trichuris sp. and Oesophagostomum sp. were highest in the troop (Da Gama Park) with the most frequent human interactions. The series of potential host-intrinsic and host-extrinsic determinants of host-parasite dynamics failed to explain the observed inter-troop variations in parasite infections. Molecular analyses of the ubiquitous and highly prevalent nematode, Trichuris sp., provided evidence of two genetically distinct Trichuris species, including a newly identified baboon parasite, named T. papionis, and another that strongly resembles (91% similarity between ITS1-5.8S rDNA-ITS2 sequences) the human T. trichiura. The latter finding provides the first evidence of a likely reverse zoonotic infection of baboons with human parasites.
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