Prevalence of Antibodies to Japanese Encephalitis Virus and Severe Fever with Thrombocytopenia Syndrome Virus in Wild Boars Captured Across Different Locations in Toyama Prefecture, Japan

Wild boars inhabit fields, hills, and farms across Japan, where they are fed on by numerous arthropods, including mosquitoes and ticks. Consequently, they are frequently exposed to arthropod-borne pathogens. In Toyama Prefecture, blood samples from captured wild boars have long been collected for classical swine fever virus antibody testing, with detailed records kept on the capture locations. In this study, we investigated the prevalence of antibodies against Japanese encephalitis virus (JEV) and severe fever with thrombocytopenia syndrome virus (SFTSV) using 3059 serum samples collected from wild boars over the past six years. A previously developed single-round infectious particles (SRIPs) assay system was employed for the analysis. We also examined the geographic distribution of antibody-positive wild boars. The results showed that antibody positivity rates for both JEV and SFTSV increased annually from 2019 to 2024. Geographical analysis revealed that JEV antibody-positive wild boars were distributed throughout Toyama Prefecture, whereas SFTSV antibody-positive wild boars were concentrated mainly in the northwestern region and along the western prefectural border. These findings suggest that JEV continue to pose an infection risk across the entire prefecture, while SFTSV has been actively spreading in the northwestern area during 2023-2024, raising concern over an increasing risk of human infection.