Sero-epidemiology and risk factor investigation for exposure to Japanese encephalitis virus in swine populations reared in climatically diverse regions of India

Japanese encephalitis (JE) is widely prevalent in the Asia-Pacific region. There is limited information on JE virus (JEV) seroprevalence as well as the associated epidemiologic and ecological factors in India. This study aimed to determine the seroprevalence of JEV and associated risk factors in swine populations from climatically diverse regions of the country. A total of 1205 swine serum samples were collected from the backyard/established/slaughterhouse settings of the western (Maharashtra state), northern (Uttar Pradesh state), northern temperate (Uttarakhand state), and northeastern (Assam state) zones of India. Information on demographic (swine population), geographic (paddy cultivation area) and weather (annual rainfall)-related variables was collected and analysed to understand their association with JE seropositivity. A JEV seroprevalence of 20.3% (95% CI: 17.9-22.7) using IgM and 16.6% (95% CI: 14.3-19.1) using IgG ELISA(s) was recorded, with an overall seroprevalence of 17.7% (95% CI: 15.8-19.6). The highest seroprevalence was observed in Assam state (30.2%; 95% CI: 25.9-34.7) followed by Maharashtra (17.2%; 95% CI: 13.6-21.1), Uttarakhand (13.4%; 95% CI: 10.1-17.3) and Uttar Pradesh (11%; 95% CI: 8.2-14.3). JEV seroprevalence was highest during the post-monsoon season (40.3%, 95% CI: 34.7-46.0, n = 205), followed by the monsoon (18.9%, 95% CI: 15.7-22.2, n = 410), winter (17.0%, 95% CI: 13.5-20.9, n = 290), and summer (3.7%, 95% CI: 1.9-6.2, n = 300) seasons. The final multivariable analysis indicated that odds of infection were 2.59 (95% CI: 1.77-3.81, p = 0.001) times greater in the dense swine population area (population > 7616-81872 v/s 313-2006) and 5.77 (95% CI: 3.80-8.76, p = < 0.001) times greater in the small per capita paddy area (0-0.011 v/s > 0.046-0.091 hectares). This is the first study reporting JEV seroprevalence in the swine population of the northern temperate Indian zone, and it is recommended that sentinel surveillance and JE vaccine coverage be extended to the newly reported areas of virus activity.