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Abstract :
[en] Human encroachment into natural environments has increased human-wildlife interactions, heightening the risk of zoonotic disease transmission. In Bali, Indonesia, long-tailed macaques (Macaca fascicularis) regularly interact with humans in touristic areas, creating a prime setting for potential transmission risk of zoonotic gastrointestinal (GI) parasites. GI parasites, including protozoan and helminth species, are transmitted via the fecal-oral route and are among the most common zoonotic agents shared between humans and primates. Various factors can influence GI parasite infection risk. This study aimed to explore the role of social behavior, host characteristics, and interactions with humans in the risk of infection with zoonotic GI parasites in a group of long-tailed macaques. We non-invasively and opportunistically collected 141 fecal samples from 53 identified macaques in Ubud Monkey Forest during 2022 and 2023. Fecal samples were analyzed using direct smear and flotation techniques, with GI parasites identified to the genus level through microscopic observation. We measured presence and species richness of GI parasites for each individual. We used focal sampling to quantify grooming rates among macaques and rates and macaque-human interactions. Social network analysis (SNA) allowed us to explore infection dynamics, including K-tests to determine whether GI parasite infections followed grooming pathways. Finally, we run generalized linear mixed models (GLMMs) to evaluate the effects of several risk factors on GI parasite infections. 74% of fecal samples were tested positive for at least one genus of GI parasites. Seven genera were identified: three protozoa (Entamoeba sp, Iodamoeba sp, Balantioides sp) and four helminths (Strongyloides sp, Oesophagostomum sp, Trichuris sp, and hookworms). Entamoeba sp and hookworms being the most prevalent parasites (respectively 0.71 and 0.42 of prevalence). K-tests showed no increased likelihood of infection for individuals neighboring infected cases and grooming interactions alone did not significantly account for transmission patterns. GLMMs revealed that higher eigenvector centrality in grooming network decreased parasite species richness, suggesting a social buffering effect. A non-significant positive effect of human-macaque interactions on gastrointestinal parasite species richness, retained in the final model through best model selection, was also observed, alongside a significant positive effect on the presence of the protozoan Iodamoeba sp. Our findings suggest that while grooming and social centrality play a role, other factors—such as human-macaque interactions and environmental contamination—are likely contributing to the GI parasites infection dynamics.
