The detection of Japanese encephalitis virus (JEV) in the Murray region, New South Wales: a public health investigation.

Abstract: The detection of Japanese encephalitis virus (JEV) in pigs, at four piggeries in the Murray region in February 2022, prompted a public health investigation (PHI) by the New South Wales Department of Health (NSW Health) to identify people at greatest risk of infection. The PHI included three components: a vaccination clinic and accompanying clinic questionnaire; a serological investigation; and a cross-sectional study for consenting Australian-born participants who completed an extended questionnaire after receiving their serological results. The goals were to vaccinate a presumably naïve population to reduce associated risk and to understand the seroprevalence among Australian-born piggery workers. A total of 322 farm workers and/or residents attended clinics organised by NSW Health; 311 received a JEV vaccine (96.6%); and 302 (94%) completed a clinic questionnaire. Of 178 people from whom serology was collected (55.3%), a total of 165 returned Defined Epitope Blocking enzyme-linked immunosorbent assay (DEB ELISA) results; 153/165 of those returning DEB ELISA results were Australian born. The study's cross-sectional component involved 129 participants, ten of whom were seropositive. The overall seropositivity for 153 Australian-born participants across the identified piggeries was 6.5% (95% confidence interval [95% CI]: 3.4-12.0%), suggesting that JEV was circulating in piggeries, and plausibly more broadly, within the Murray region prior to serology collection. Male sex and working on, or visiting, a farm other than their regular workplace were both associated with JEV seropositivity (odds ratio [OR]: 5.4; 95% CI: 0.94-137.1 and OR: 37; 95% CI: 0.92-22.08 respectively). JEV vaccination uptake was high among piggery workers in the Murray region. Further studies are needed to determine if piggery workers have an increased risk of developing JEV compared to people who do not work or live on JEV-affected piggeries. The reasons for the emergence of JEV in pigs in the Murray region remain unclear.