When conservation meets contagion: Mapping yellow fever risk to guide vaccination in an endangered primate

Emerging infectious diseases pose a growing threat to global biodiversity. During Brazil's 2017–2019 yellow fever (YF) outbreak, approximately 30% of the endangered golden lion tamarin (GLT) ( Leontopithecus rosalia ) population was lost—highlighting the vulnerability of wildlife to such epidemics. YF is a vector‐borne disease transmitted by forest‐dwelling mosquitoes, with landscape structure and human modification potentially influencing transmission dynamics. However, the environmental drivers of YF mortality in wild primate populations, and how they shift between outbreak and non‐outbreak periods, remain largely unknown. In this study, we investigated the impact of YF outbreak on GLT mortality and examined the environmental factors that may have facilitated the spread and severity of the disease. Using data derived from three decades of monitoring (1989–2022) and modelling approaches (e.g. generalized linear models and spatial mapping), we compared survival patterns during the 2017–2019 YF outbreak to those from an immediately preceding outbreak‐free period (2014–2016). We modelled the probability that GLTs survived each year as a function of forest cover, fragment connectivity, human population density, road proximity and group size. Landscape and demographic factors showed different effects during outbreak versus non‐outbreak years. While habitat connectivity enhanced survival before the outbreak, it amplified mortality during the YF outbreak, highlighting the context‐dependent effects of landscape features on wildlife populations. Human‐modified environments had minimal impact on GLTs prior to the outbreak, but promoted mortality during the outbreak, likely by facilitating contact with infected mosquito vectors in edge habitats and disturbed forest patches. In contrast, climatic variables did not emerge as significant predictors of survival. Synthesis and applications : Spatial projections revealed high‐risk areas for YF transmission, highlighting priority zones for targeted vaccination efforts in GLTs. By integrating disease ecology into conservation planning, this study offers a scalable framework for spatially informed interventions aimed at mitigating disease‐driven declines in threatened species.