Conservation efforts have led to the recovery of the endangered mountain gorilla populations. Due to their limited potential for spatial expansion, population densities increased, which may alter the epidemiology of infectious diseases. Recently, clinical gastrointestinal illnesses linked to helminth infections have been recorded in both gorilla populations. To understand drivers and patterns of helminth infections we quantified strongylid and tapeworm infections across both Virunga Massif and Bwindi populations using fecal egg counts. We assessed the impact of age, sex, group size, season and spatial differences used as a proxy, which reflects observed variation in the occurrence of gastrointestinal problems, vegetation types, gorilla subpopulation growth and associated social structure on helminth infections. We revealed striking geographic differences in strongylid infections with higher egg counts mostly in areas with high occurrences of gastrointestinal disease. Increased helminth egg counts were also associated with decreasing group size in some areas. Observed spatial differences may reflect mutual effects of variations in subpopulation growth rates, gorilla social structure, and vegetation associated with altitude across mountain gorilla habitat. Helminth infection intensities in Virunga gorillas were lowest in the youngest and the oldest animals. Elucidating parasite infection patterns of endangered species with low genetic diversity is crucial for their conservation management.

Infectious diseases including those caused by parasites can be a major threat to the conservation of endangered species. There is thus a great need for studies describing parasite infections of these species in the wild. Here we present data on parasite diversity in an agile mangabey (Cercocebus agilis) group in Bai Hokou, Dzanga-Sangha Protected Areas (DSPA), Central African Republic. We coproscopically analyzed 140 mangabey fecal samples by concentration techniques (flotation and sedimentation). Agile mangabeys hosted a broad diversity of protistan parasites/commensals, namely amoebas (Entamoeba spp., Iodamoeba buetschlli), a Buxtonella-like ciliate and several parasitic helminths: strongylid and spirurid nematodes, Primasubulura sp., Enterobius sp., and Trichuris sp. Importantly, some of the detected parasite taxa might be of potential zoonotic importance, such as Entamoeba spp. and the helminths Enterobius sp., Trichuris sp., and strongylid nematodes. Detailed morphological examination of ciliate cysts found in mangabeys and comparison with cysts of Balantioides coli from domestic pigs showed no distinguishing structures, although significant differences in cyst size were recorded. Scanning or transmission electron microscopy combined with molecular taxonomy methods are needed to properly identify these ciliates. Further studies using molecular epidemiology are warranted to better understand cross-species transmission and the zoonotic potential of parasites in sympatric non-human primates and humans cohabiting DSPA.