Parasitological and molecular characterization of gastrointestinal parasites in free-ranging capybaras (Hydrochoerus hydrochaeris) from urbanized environments in Rio de Janeiro, Brazil

Free-ranging capybaras ( Hydrochoerus hydrochaeris ) have increasing epidemiological importance as reservoirs of gastrointestinal parasites that may contribute to parasite circulation at the wildlife–domestic animal–human interface. This study aimed to characterize the gastrointestinal parasitic fauna of capybaras from two urbanized areas in the municipality of Rio de Janeiro, southeastern Brazil, using integrated coproparasitological and molecular approaches. A total of 25 fecal samples were collected directly from captured animals between May 2024 and September 2025. Coproparasitological analyses included flotation, McMaster egg counting, coproculture, the Baermann technique, and oocyst sporulation, whereas molecular analyses included PCR amplification and sequencing of the 18S and 28S rRNA genes. Overall, 80.0% (20/25) of the samples were positive for at least one parasite taxon. Eimeria spp. showed the highest prevalence (56.0%; 14/25), followed by Strongyloides spp. (44.0%; 11/25) and members of the family Trichostrongylidae (28.0%; 7/25). Capillariidae and Oxyuridae were each detected in 12.0% (3/25) of the animals, whereas Monoecocestus sp. and morphologically identified Protozoophaga obesa were detected in 8.0% (2/25). Mixed infections occurred in 65.0% (13/20) of the positive animals. Morphometric analysis identified four Eimeria species, with E. trinidadensis predominating in Manguinhos and E. ichiloensis in Santa Cruz. Molecular analyses supported the identification of Protozoophaga sp. and identified gastrointestinal nematodes belonging to the families Trichostrongylidae and Strongyloididae. Sequences showing high similarity to Caenorhabditis briggsae were also detected, suggesting pseudoparasitism or environmental contamination. These findings expand current knowledge of the gastrointestinal parasitofauna of free-ranging capybaras and demonstrate the value of integrating coproparasitological and molecular approaches for parasite characterization.