Japanese Encephalitis Virus Sylvatic co-occurrence probabilities under a changing climate

Japanese Encephalitis is a growing concern in Australia. This follows the first outbreak of cases of the tropical disease in southern Australia in 2022. The sylvatic cycle of Japanese encephalitis virus (JEV) includes waterbirds as reservoir hosts and mosquito vectors. The human risk of infection from JEV is increased by the presence of amplifying host species such as feral pigs. The spatial distribution of these species may be sensitive to a changing climate, potentially increasing or decreasing the risk of outbreaks. In this study, we aim to investigate how spatial distributions of vectors and hosts may change under different climate change scenarios, by mapping JEV species co-occurrence probabilities in Australia on a national scale. Maximum Entropy modelling was used to develop species distribution models within Australia for three mosquito species, 12 species of Australian waterbirds, and feral pigs. A sylvatic co-occurrence probability (CoP) was calculated by merging projected presence probabilities for each species for the 2025, 2050 and 2090 climatic periods. Climate projections were sourced for eight climate models under a high (RCP 8.5) and low (RCP 4.5) climate change scenario based on CMIP-5 projections. Results showed that coastal regions with high climatic suitability for species co-occurrence were unlikely to change greatly under these climate projections. Mosquito presence probabilities and hence JEV CoP, were most consistently associated with temperature range and aridity climate indices, though high collinearity among candidate predictors limits causal inference. Our results highlight the need to understand climate effects on all the species in the transmission cycle and ultimately suggested that current regions of relatively high climatic suitability for species co-occurrence will remain high in the future.