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