Abstract

Background: Environmental and biological factors can regulate host-parasite interactions. However, in the context of habitat alteration due to human-induced activities, little is known about its effects on parasite infections in wildlife populations. This study focused on the study of 363 wild rodents (Phyllotis darwini Waterhouse 1837) inhabiting two areas with different anthropogenic pressures (i.e., non-altered [protected] and altered [rural] area) in the Coquimbo Region, in Chile, during five consecutive seasons (2021–2022). Coprological examinations were carried out using the Mini-FLOTAC method, and factors associated with parasite infections (i.e., seasons, site types, sex, and body mass) were evaluated. Results: The overall prevalence of gastrointestinal parasitism was 74.9% (272/363), and 16 parasite taxa were found, some of which were reported for the first time in P. darwini, such as Archiacanthocephala, Ascaridina, Trichosomoididae, Schistosoma sp., Isospora spp., Giardia sp., and Entamoebidae. The best predictors of parasitism included type of site, seasonality, and body condition. The infection probability and density (as eggs/oocysts per gram of feces) of some parasite taxa were lower in rodents inhabiting the rural area compared to those in the protected area, but no difference was observed in the gastrointestinal parasite richness according to the type of site. Seasonal effects were also observed, with a higher likelihood of parasite infection and greater parasite richness in winter and spring of 2022 in both protected and rural areas. Rodents with higher scaled body mass index showed higher likelihood of parasite infection and higher parasite richness in both kinds of areas. Sex-biased parasitism was not detected in adults. Conclusions: The results presented in this one-year study indicate that gastrointestinal parasites in Phyllotis darwini in north-central Chile are influenced by habitat alteration, seasonality, and body mass. Reduction of host populations due to anthropogenic effects may limit parasite transmission in altered sites. Non-native hosts may still introduce new species to the parasite fauna of P. darwini in the altered area. Seasonal patterns may be explained by favorable biotic and abiotic conditions during wetter winter, for both hosts and developmental parasitic stages, including time-lagged effects extended into spring. Finally, larger rodents may show higher exposure to parasite transmission. © The Author(s) 2025.