Insights into the threats of toxoplasmosis for free-ranging black-tufted marmosets living in our neighborhood.

Toxoplasmosis is a globally significant zoonotic disease with the potential to severely impact wild animal populations. Neotropical non-human primates (NHPs), particularly callitrichids, are highly susceptible, often experiencing fatal outcomes. This study examines toxoplasmosis in free-ranging black-tufted marmosets (Callithrix penicillata) in anthropogenic environments of Central Brazil, analyzing epidemiological and pathological data from 2017 to 2022. A retrospective review of 1095 NHP deaths identified a 9.2% prevalence (101/1,095) of acute fatal toxoplasmosis (AFT) in black-tufted marmosets across Central Brazil and 10.3% (53/515) within the federal district (FD). Necropsied marmosets from the FD showed an estimated AFT prevalence of 50.7% and a lethality rate of 20.3%. AFT cases were linked to outbreaks and isolated incidents, with a likely seasonal peak during the dry season. Pathological findings included severe hepatic damage, splenitis, interstitial pneumonia, and myocarditis. Immunohistochemistry and qPCR confirmed Toxoplasma gondii infection, with the highest parasite loads in the spleen and liver. Given the anthropogenic pressures of habitat fragmentation, urbanization, and T. gondii exposure, this study advances the understanding of toxoplasmosis as an emerging disease in wild marmosets. Findings of this study establish a critical foundation for conservation strategies and insights into toxoplasmosis dynamics in free-ranging NHPs living in our neighborhood.