Parasite transmission risk from geophagic and foraging behavior in chacma baboons.

Numerous behavioral and ecological factors are associated with parasite transmission. One factor explored in human research, but absent from nonhuman primate research, is parasite transmission from soil ingestion. Human studies suggest geophagy, the regular and deliberate consumption of soil, increases risk of soil-transmitted helminth (STH) infection. Geophagy, which is prevalent in nonhuman primates, has several positive associations: gastrointestinal distress alleviation, possible mineral supplementation, and bacterial infection prevention. Our objective was to determine whether STH transmission was possible from deliberate or accidental soil ingestion, in a troop of chacma baboons (Papio hamadryas ursinus) that engaged in geophagy, foraged on the terrestrial substrata, and had a Trichuris sp. sample prevalence of 100%. We collected and analyzed 80 soil samples from geophagy and ground foraging sites on and around Wildcliff Nature Reserve, South Africa. Forty soil samples were collected from sites where soil was consumed, and 40 were collected from sites where soil was not consumed. At geophagy sites, the number of Trichuris sp. eggs recovered varied significantly between areas used and unused by the baboons, suggesting behavior is an important factor. In contrast, at foraging sites, there was only a tendency to recover more eggs at used than unused areas, and we propose egg recovery was influenced by fecal contamination that occurred throughout foraging stands. The difference in egg recovery between used areas at geophagy sites and used areas at foraging sites was not significant. These preliminary findings suggest both geophagy and foraging sites are a potential source of STH infection for this troop. Whether geophagy benefits outweigh the potential cost of parasite reinfection for this baboon troop is unknown, so we encourage future research on the influence that host foraging behavior may have on parasite reinfection.