Little pig, little pig, let me come in: The influence of landscape structure and La Niña climatic anomalies on the emergence of Japanese encephalitis virus in Australian piggeries in 2022

The widespread activity of Japanese encephalitis virus (JEV) in previously unaffected regions of eastern and southern Australia in 2022 represents the most significant local arbovirus emergency in almost 50 years. Japanese encephalitis virus is transmitted by mosquitoes and maintained in wild ardeid birds and amplified in pigs, the latter of which suffer significant reproductive losses as a result of infection. The landscape of JEV outbreak risk in mainland Australia is almost entirely unknown, particularly in the eastern and southern parts of the country where the virus has not been previously documented. Although other areas with endemic JEV circulation in the Indo-Pacific region have demonstrated the importance of wild waterbird-livestock interface in agricultural-wetland mosaics, no such investigation has yet determined the configuration of pathogenic landscapes for Australia. Moreover, the recent emergence in Australia has followed substantial precipitation and temperature anomalies associated with the La Niña phase of the El Niño Southern Oscillation. This study investigated the landscape epidemiology of JEV outbreaks in Australian piggeries recorded between January and April of 2022 to determine the influence of ardeid habitat suitability, hydrogeography, hydrology, land cover and La Niña-associated climate anomalies in demarcating risk. Outbreaks of JEV in domestic pigs were associated with ardeid species richness, agricultural and riparian landscape mosaics, hydrological flow accumulation, and grasslands. This study has identified the composition and configuration of landscape features that delineated risk for piggeries during the 2022 emergence of JEV in Australia. Although preliminary, these findings can inform actionable strategies for the development of new One Health JEV surveillance specific to the needs of Australia.