First Report of Mansonella sp. Microfilariae in Sapajus nigritus: Insights into the Host-Parasite Relationship

Abstract Primates can share parasites with humans, and understanding host-parasite interactions is essential for evaluating the condition of wild primates, ecological dynamics, and One Health interface, which integrates humans, animal, and environmental health in shared environments. One example is filarial nematodes of the genus Mansonella , for which a lack of in-depth studies of symptoms or blood alterations limits our understanding of their impact on host health and parasite-host dynamics in wild populations. We investigated microfilariae in Sapajus nigritus on Marambaia Island in Rio de Janeiro, Brazil. We also evaluated the host-parasite relationship by assessing the association between microfilarial load with physical and hematological parameters of the hosts. We captured 27 S. nigritus and screened them for microfilariae using blood samples via microscopy—based on morphological and morphometric characteristics—and polymerase chain reaction (PCR), followed by ITS1 sequencing for molecular species identification. We also assessed physical and hematological parameters. We detected microfilariae in 25 individuals (93%) by PCR and in 22 (81%) by microscopy with high mean intensity, mean abundance, and parasite load. We classified the infected S. nigritus as healthy based on both physical and hematological parameters. A multivariate linear model revealed a significant positive association between Mansonella sp. load and red blood cell parameters, while associations with white blood cell parameters were negative and nonsignificant. These results suggest that S. nigritus coexists with Mansonella sp. microfilariae without apparent clinical signs of disease, potentially indicating immunological tolerance. Our findings highlight the importance of understanding host-parasite interactions in wild primates, particularly in environments where human-primate interfaces may occur, suggesting a potential risk of cross-species parasite transmission.