Serological evidence of Japanese encephalitis virus infection in pigs in a low human incidence state, Goa, India

Abstract

Japanese encephalitis (JE) is a mosquito-borne zoonosis caused by Japanese encephalitis virus (JEV). It is a leading cause of encephalitis in humans especially children in Asia. Aquatic wading birds are the reservoirs and pigs serve as amplifying hosts for JEV. Humans and horses are dead-end hosts. JE is endemic in several states of India. Goa, a small state on the west coast of India, had witnessed JE outbreaks in the past and as on date human JE cases are reported sporadically. Although human JE cases are well documented in Goa, the status of JEV exposure of pigs has not been well documented. Hence the present study was undertaken with an objective of identifying JEV exposure in the pig population of Goa state in the light of declining human JE cases. To achieve the objective, between January 2017 and May 2019, serum samples from 666 pigs were screened using enzyme-linked immunosorbent assay (ELISA) for the detection of anti-JEV IgG. The apparent prevalence of anti-JEV IgG in pigs was found to be 7.1 % (95 % confidence interval 5.3 %-9.3 %) and true prevalence was 4.6 % (95 % confidence interval 2.7 %-7.1 %). The seroprevalence of JE recorded in pigs of Goa state was low compared to other endemic states in India, which may also be one of the reasons for the lower prevalence of human JE cases in Goa state. Univariate analysis revealed that the age of the pigs and district did not significantly influence the JE seroprevalence in pigs of Goa state. However, in multivariable logistic regression, the North Goa district was found to significantly (p = 0.017) influence the JE seroprevalence in pigs. The study identified that JEV is still circulating in the Goan pig population and hence constant vigil is required to monitor the intensity of JEV circulation in pigs. Besides forewarning possible human outbreaks in the locality, evidence of JEV exposure in pig population provides valuable data on the magnitude and extent of geographical spread.