American Journal of Primatology 71:1–7 (2010) RESEARCH ARTICLE Patterns of Gastro-Intestinal Parasites and Commensals as an Index of Population and Ecosystem Health: The Case of Sympatric Western Chimpanzees (Pan troglodytes verus) and Guinea Baboons (Papio hamadryas papio) at Fongoli, Senegal MICHAELA E. HOWELLS 1 , JILL PRUETZ 2 , AND THOMAS R. GILLESPIE 3,4Ã 1 Department of Anthropology, University of Colorado, Boulder, Colorado 2 Department of Anthropology, Iowa State University, Ames, Iowa 3 Department of Environmental Studies and Program in Population Biology, Ecology and Evolution, Emory University, Atlanta, Georgia 4 Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia The exponential decline of great apes over the past 50 years has resulted in an urgent need for data to inform population viability assessment and conservation strategies. Health monitoring of remaining ape populations is an important component of this process. In support of this effort, we examined endoparasitic and commensal prevalence and richness as proxies of population health for western chimpanzees (Pan troglodytes verus) and sympatric guinea baboons (Papio hamadryas papio) at Fongoli, Senegal, a site dominated by woodland-savanna at the northwestern extent of chimpanzees’ geographic range. The small population size and extreme environmental pressures experienced by Fongoli chimpanzees make them particularly sensitive to the potential impact of pathogens. One hundred thirty- two chimpanzee and seventeen baboon fecal samples were processed using sodium nitrate floatation and fecal sedimentation to isolate helminth eggs, larvae, and protozoal cysts. Six nematodes (Physaloptera sp., Ascaris sp., Stronglyloides fuelleborni, Trichuris sp., an unidentified hookworm, and an unidentified larvated nematode), one cestode (Bertiella sp.), and five protozoans (Iodamoeba buetschlii, Entamoeba coli, Troglodytella abrassarti, Troglocorys cava, and an unidentified ciliate) were detected in chimpanzee fecal samples. Four nematodes ( Necator sp., S. fuelleborni, Trichuris sp., and an unidentified hookworm sp.), two trematodes (Shistosoma mansoni and an unidentified fluke), and six protozoans (Entamoeba histolytica/dispar, E. coli, Chilomastix mesnili, Balantidium coli, T. abrassarti, and T. cava) were detected in baboon fecal samples. The low prevalence of pathogenic parasite species and high prevalence of symbiotic protozoa in Fongoli chimpanzees are indicative of good overall population health. However, the high prevalence of pathogenic parasites in baboons, who may serve as transport hosts, highlight the need for ongoing pathogen surveillance of the Fongoli chimpanzee population and point to the need for further research into the epidemiology and cross-species transmission ecology of zoonotic pathogens at this site. Am. J. Primatol. 71:1–7, 2010. r 2010 Wiley-Liss, Inc. Key words: Africa; apes; disturbance ecology; zoonoses INTRODUCTION With fewer than 200,000 remaining individuals and a yearly population decline of 4.7%, chimpanzees (Pan troglodytes) are one of the most threatened primates in Africa [Goodall, 1983, 1986, 1988]. The compounded pressures of human population growth, commercial logging, and the bushmeat trade have resulted in significant population declines in chim- panzee populations across the continent [Butynski, 2003]. In recent years it has become clear that in addition to these pressures, pathogens can also dramatically impact chimpanzee populations as evidenced by high rates of mortality in wild chimpan- zee populations associated with anthropozoonotic transmission of human respiratory viruses [Kaur et al., 2008; Kondgen et al., 2008] and the natural Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ajp.20884 Received 12 January 2010; revised 11 August 2010; revision accepted 11 August 2010 Contract grant sponsors: National Geographic Society; The Explorers Club; The American Society of Primatologists Con- servation Grant; Sigma Xi Grant in Aid; Iowa State University’s Department of Anthropology and College of Liberal Arts and Sciences; Emory University; University of Illinois. Ã Correspondence to: Thomas R. Gillespie, E510 Math and Science Center, 400 Dowman Drive, Emory University, Atlanta, GA 30322. E-mail: thomas.gillespie@emory.edu r r 2010 Wiley-Liss, Inc.