Seasonal effects in gastrointestinal parasite prevalence, richness and intensity in vervet monkeys living in a semi‐arid environment

Parasite and pathogen incidence and prevalence is driven by both periodic variation in environmental conditions and host characteristics. Given the increasing risk of zoonotic transmission to humans, and the close phylogenetic relationship between humans and non‐human primates, understanding this variation in parasite dynamics is becoming essential for epidemiologists and conservationists alike. The extreme seasonal temperatures coupled with declining annual rainfall and severe periodic drought of the semi‐arid Karoo poses distinct challenges to both hosts and pathogens and serves as a window into how animals confront climate change‐induced environmental changes. Here we quantified annual variation in gastrointestinal parasite prevalence, intensity and richness in three troops of wild vervet monkeys ( Chlorocebus pygerythrus ) and determined what climatic variables were driving these changes. Further, we assessed whether there is long‐term temporal dependence in intra‐individual faecal egg counts. We found variation in the prevalence of five genera of helminths identified in the study population, but little variation in parasite richness across the year. Such variation was driven primarily by precipitation and maximum daily temperature. Finally, we found structure in faecal egg counts, suggesting that contrary to previous findings, egg shedding of Trichostrongylus sp. and ? Protospirura sp. are not stochastic processes and may serve as an indicator of individual levels of infection in our population. Combined, these results provide the first report of seasonal effects in gastrointestinal parasites of vervet monkeys living in an extreme environment.