Summary
Japanese encephalitis (JE) is endemic in India. Although pigs are considered an important amplifier host as well as sentinels for JE outbreaks in people, limited information is available on JE virus (JEV) surveillance in pigs. We investigated the spatio-temporal distribution of JEV seroprevalence and its association with climate variables in 4451 pigs sampled from 10 districts in eastern Uttar Pradesh, India over a 10 year period (2013—2022).
The mean seroprevalence of IgG (2013-2022) and IgM (2017—2022) was 14% (95% CI 12.8—15.2) and 10.98% (95% CI 9.8—12.2), respectively. Throughout the region, higher seroprevalence from 2013—2017 was observed, and was highly variable with no predictable spatio-temporal pattern between districts. Seroprevalence of up to 60.8% in Sant Kabir Nagar in 2016 and 69.5% in Gorakhpur district in 2017 for IgG and IgM was observed, respectively. IgG seroprevalence did not increase with age. Monthly time series decomposition of IgG and IgM seroprevalence demonstrated annual cyclicity (3-4 peaks) with seasonality (higher, broader peaks in the summer and monsoon periods). However, most variance was due to the overall trend and the random components of the time series. Autoregressive time-series modelling of pigs sampled from Gorakhpur was insufficiently predictive for forecasting; however, an inverse association between humidity (but not rainfall or temperature) was observed.
The results confirm year-round endemicity in pigs in eastern Uttar Pradesh. Transient IgG suggests that JEV might not be immunising in pigs, which needs further investigation; some models that inform public health interventions for JEV assume long-term immunity in pigs. Although pigs are used as sentinels for human outbreaks, we find that most variability in pig seroprevalence is not due to underlying trend or annual cyclicity. Therefore, autoregressive models using broad climate variables are most likely insufficiently nuanced to inform public health interventions for JEV prevention in people.
Keywords: time series; Japanese encephalitis virus; India; spatial epidemiology; swine