25 years of non-human primates surveillance contributing to yellow fever control in Brazil.

Yellow fever (YF) remains a major zoonotic disease in tropical regions of the Americas and Africa. In Brazil, surveillance of epizootics in non-human primates (NHPs) has become a cornerstone of YF prevention and control. This study provides a historical overview of NHP epizootic surveillance in Brazil from 1999 to 2025 and evaluates its role as an early warning system for human infections within a One Health framework. A retrospective descriptive epidemiological study was conducted using surveillance data from the Notifiable Diseases Information System (SINAN) and the Wildlife Health Information System (SISS-Geo). Records of YF epizootics in NHPs and confirmed human YF cases were analyzed according to geographic region, biome, seasonality, and taxonomic identification. During the study period, 35,496 epizootics involving 43,062 NHPs were reported, of which 3203 (9.0%) were confirmed as YF. The Southeast region accounted for the most notifications, particularly in the states of São Paulo and Minas Gerais. Three major waves of viral dispersion were identified, with the largest occurring during 2016/2017 and 2017/2018. A strong positive correlation was observed between NHP epizootics and human YF cases (r = 0.72; p < 0.001), reinforcing the sentinel role of NHPs. Epizootics generally preceded human cases, especially during the pre-seasonal period. Alouatta was the genus most frequently associated with confirmed infections. Despite advances in surveillance, important regional disparities and logistical limitations persist, particularly in the Amazon region. These findings highlight the strategic importance of integrated NHP surveillance for early outbreak detection, vaccination planning, and prevention of YF transmission in Brazil.