BACKGROUND
Yellow fever virus (YFV) has caused substantial human disease in Brazil, driven by spillover from outbreaks in nearby non-human primates (NHPs). As disease surveillance in NHPs is challenging, the impact of environmental conditions on YFV outbreaks in NHPs remains poorly understood. In this study, we aimed to use joint inference modelling to overcome these obstacles by integrating diverse data streams and to estimate YFV transmission dynamics in NHPs to enhance understanding of yellow fever disease ecology.
METHODS
We applied a multistage analysis using epidemiological, phylogenetic, demographic, and meteorological data in conjunction with mechanistic and statistical modelling. We used EpiFusion joint inference models to infer YFV infection dynamics in NHPs from 2015 to 2019, and statistical generalised additive models to test hypothesised associations between NHP infections and environmental variables and human cases.
FINDINGS
The effective reproduction number (Rt) of YFV in NHPs was approximately 1·0, indicating that small changes in transmissibility can enable explosive sylvatic outbreaks. We also found the possibility of large, entirely unobserved outbreaks in NHPs. El Niño sea surface temperature anomalies at medium-term and long-term lags were important predictors of YFV infection dynamics in NHPs. Finally, we found that the risk of YFV spillover to humans, measured in terms of the effect of NHP infections on human cases, was correlated with the number of NHP infections, with a 7-day to 21-day lag.
INTERPRETATION
YFV might be establishing recurrent transmission in NHP populations in southeast Brazil, indicating that more comprehensive and consistent surveillance is needed. Identifying key environmental drivers and their lags with human YFV cases can be used to develop early warning systems to guide reactive vaccination and public health campaigns to prevent future outbreaks.
FUNDING
None.
C. Judge, F. Iani, E. Finch et al.· Lancet Planetary Health· 0 citations
The 2026 Bundibugyo virus outbreak emerged in a region with frequent conflict, food insecurity, rainforest and mining-related human mobility in Ituri province in the north-eastern region of the Democratic Republic of Congo (DRC). Existing ecological niche models have identified regions environmentally suitable for orthoebolavirus circulation but do not explicitly account for anthropogenic conditions that shape opportunities for interspecies contact, such as wildlife-to-human, and zoonotic spillover. Here, we update habitat suitability models for three putative orthoebolavirus reservoir bat species and for orthoebolavirus, and develop an integrated spatial spillover risk framework that combines ecological suitability with anthropogenic drivers, including human settlement, mining activity, bushmeat-related activities, forest loss, and conflict. We find that the updated model reveals previously under-predicted suitability in eastern DRC, and that the integration of anthropogenic factors with orthoebolavirus habitat suitability improves the prediction of historical zoonotic spillover locations. Boyce Index (measure of spatial predictive accuracy) increases from 0.78 to 0.97 when ecological suitability was combined with the built environment, while mining- and bushmeat-based scenarios showed the greatest enrichment of observed spillover events. We also find a temporal association of the relative contribution of habitat suitability and anthropogenic factors, with mining showing the largest and most consistent effect over the last decade, and conflict acting as a secondary amplifying factor whose apparent contribution has grown in recent periods. Together, these findings demonstrate that ecological suitability alone does not fully characterize landscapes vulnerable to Ebola zoonotic emergence and highlight the value of integrating environmental and anthropogenic information to strengthen One Health surveillance, epidemic preparedness, and targeted public health interventions in the DRC and neighboring countries.
M. Moir, H. Tegally, D. M. Moges et al.· medRxiv· 0 citations
