Importance of Epizootic Surveillance in the Epidemiology of Yellow Fever in South America

Purpose of Review: Yellow fever (YF), a mosquito-borne viral hemorrhagic disease, remains a significant public health concern in South America. This review evaluates the critical role of epizootic surveillance, particularly in non-human primates (NHPs), in understanding the epidemiology of yellow fever, focusing on recent outbreaks in Brazil and Colombia during 2024–2025. Recent Findings: The review underscores the growing importance of NHPs, especially howler monkeys (Alouatta spp.), as sentinel species for the early detection of yellow fever virus (YFV) circulation. From January to May 2025, more than 100 epizootic events were reported in Brazil and Colombia, frequently preceding or coinciding with human cases. Advances in molecular diagnostics, ecological modeling, and entomovirological surveillance have further highlighted the value of a One Health approach. Nevertheless, persistent challenges such as underreporting, limited vector surveillance, and ecological disturbances impede effective disease monitoring. Summary: Epizootic surveillance in NHPs is a vital early warning system for yellow fever outbreaks. Strengthening integrated surveillance networks and prioritizing high-risk areas will enhance outbreak preparedness and guide targeted vaccination strategies throughout South America.