Exposure and susceptibility drive reinfection with gastrointestinal parasites in a social primate

1. Increased risk of infectious disease transmission has been proposed as one major cost of group living. While factors corresponding to transmission via exposure to infectious stages and susceptibility to infections upon contact are relatively well understood, both aspects are rarely investigated simultaneously.
2. Here, we assessed the influence of exposure and susceptibility measures on strongyle nematode reinfection after experimental deworming of Barbary macaques (Macaca sylvanus) (n=57). We investigated impacts of behaviour (social bonds, grooming and ground use) and physiology (faecal glucocorticoids, urinary C-Peptides, urinary neopterin, gastrointestinal [GI] helminth coinfection) on the likelihood of reinfection, using patch occupancy modelling and information theoretic model selection to determine the best models predicting reinfection patterns.
3. Coinfection was the most consistent risk factor, spending time on presumably contaminated soil, interacting with many partners and forming strong same sex bonds also tended to increase infection risk. In contrast, strong social bonds with opposite sex partners had a consistently protective effect.
4. Our results indicate that coinfections could serve as an integrative measure of individual disease susceptibility. Furthermore, we show that social contact contributes to both exposure and susceptibility to environmentally transmitted parasites, with the outcome depending on specific interactions patterns.