Seroprevalence of Japanese encephalitis virus and other flavivirus-specific antibodies among Australian blood donors following a novel epidemic spread of Japanese encephalitis virus: a cross-sectional study

Abstract

Abstract Objectives In 2022, Japanese encephalitis virus (JEV) was detected in humans and animals across mainland Australia. We examined the prevalence of JEV and endemic flaviviruses, Murray Valley encephalitis virus (MVEV) and Kunjin virus (KUNV) antibodies in blood donors in different risk geographic areas across southern Australia. Design Prospective cross-sectional serosurvey for JEV, MVEV and KUNV-specific antibodies. Setting Southern Australia. Participants All Australian blood donors who attended nine high-risk (geographical proximity to recent human, animal and/or vector detections of JEV) and three low-risk (no competent JEV vector and no animal or human detections were nearby) donor centres between 8–26 August or 12–17 September 2022 were analysed. Primary and secondary outcome measures Seroprevalence estimates of JEV, MVEV and KUNV-specific antibodies were compared between blood donors from collection sites in areas considered high-risk and low-risk for JEV infection. Seroprevalence estimates were adjusted for age and sex after excluding donors born in JEV-endemic countries and those with documented JEV vaccination. Results JEV-specific antibody seroprevalence was 1.6% (95% CI 1.3% to 2.0%) from 5257 samples. Odds of JEV seropositivity were greater in high-risk versus low-risk areas (OR 1.8, 95% CI 1.5 to 2.2; absolute risk difference: 0.8 percentage points) and in males versus females (OR 2.1, 95% CI 1.2 to 3.6). In high-risk areas, people ≥70 years had higher seroprevalences than those aged 18–29 (OR 3.1, 95% CI 1.8 to 5.5). MVEV and KUNV-specific antibody seroprevalence were 2.2% (95% CI 1.9% to 2.7%) and 3.7% (95% CI 3.2% to 4.3%), respectively, with higher prevalence in high-risk areas (MVEV OR 2.6, 95% CI 1.6 to 4.3; KUNV OR 2.4, 95% CI 1.9 to 3.0) and older ages. Conclusions Blood donors in areas where JEV emerged in the 2021–2022 Australian summer had a 0.8 percentage point higher seroprevalence compared with non-JEV transmission areas, with older male donors most likely to be seropositive. Patterns were similar for endemic flaviviruses. This data informed recommendations for JEV vaccine distribution to high-risk areas and the need for non-pharmaceutical mosquito prevention strategies across Australia, given the highly susceptible population.