Spatiotemporal dynamics and determinants of yellow fever outbreaks in 21st century Brazil: an ecological study

BACKGROUND: Yellow fever (YF) is a highly lethal arboviral disease that is transmitted to humans by the bites of infected mosquitoes. However, the drivers of epidemic episodes are not well understood. In this ecological study, we analysed spatial and temporal patterns of the largest yellow fever outbreaks in the 21st century in Brazil. METHODS: We describe the spatial and temporal patterns of 2178 human YF cases, 2911 non-human primate (NHP) cases and immunization coverage using the Global and Local Moran's Index, directional distribution and logistic regression models. RESULTS: Spatially distinct clusters were detected along heterogeneous forestland and ecological corridors. Human YF occurrence increased with a higher abundance and diverse genera of NHP YF cases along with seven other variables: lower vaccination coverage, lower elevation, moderate annual mean temperature, higher annual precipitation, increased vector abundance, low to moderate urbanization and forested land. CONCLUSIONS: Our results suggest that human YF epidemics are largely driven by vaccination coverage and environmental conditions that aid transmission in vectors and hosts. This sustains the local sylvatic cycle across administrative and political boundaries. These results reinforce the need to study YF spillover and dispersion dynamics at the human-animal-environment interface to improve disease control and devise multisectoral mitigation strategies.