Sero-prevalence of West Nile virus in urban and peri-urban poultry farms of Guwahati, India

West Nile virus (WNV) is a zoonotic, emerging mosquito-borne virus which can cause severe disease in the form of encephalitis and acute flaccid paralysis in humans. In Assam, northeast India, arboviruses seem to be re-emerging, however, WNV has been little studied. The present investigation was carried out from April, 2018 to March, 2019 to study sero-positivity of WNV in chicken in urban and peri-urban areas of Guwahati, the capital city of Assam. Four urban and four peri-urban areas of Guwahati were selected. A total of 864 chicken serum samples (72 samples per month) were screened by ELISA and further confirmed by haemagglutination inhibition (HI), which revealed that 3.13% of the chickens had been exposed to WNV, with 0.69% sero-positivity in urban areas compared to 5.56% in peri-urban. Peak sero-prevalence of WNV were reported during the month of July and August with 8.33% each with lowest sero-prevalence being recorded in November (1.39%) and no sero-positive birds from December to April. These results indicate that WNV is one of the actively circulating flaviviruses in Assam, and human febrile and encephalitic cases should be screened for the disease

Mosquito abundance and pig seropositivity as a correlate of Japanese encephalitis in human population in Assam, India

Background & objectives: Assam is the most vulnerable state for Japanese encephalitis (JE) in India. The situation warrants characterization of epidemiological patterns of JE in vectors, pigs and human population. This investigation was aimed to determine the relative abundance of mosquito species and seroprevalence of JE in pigs in order to draw an epidemiological association with reported human JE cases in Assam. Methods: Pig sera and mosquitoes from selected farms in Sivasagar and Kamrup districts of Assam were collected fortnightly for one year during June 2015–May 2016. Pig sera were tested for JE antibodies by haemagglutination and virus neurtralization tests. Mosquito species were identified microscopically following the taxonomic keys. The results were analyzed with data on confirmed human JE cases in the selected districts. Results: Culex gelidus (26.07%) and Cx. tritaeniorhynchus (24.07%) were the most abundant species in collected mosquitoes (n = 997). A total of 22.99% of pigs (n = 335) were JEV seropositive and 45.65% of human acute encephalitis syndrome cases (n = 230) were positive for JE virus (JEV) infection. Relative mosquito abundance, pig positivity and human cases were highest during monsoon (June–September) and least during winter (December–February). Rise in mosquito population was observed during pre-monsoon season (March–May) and concurrently higher number of human cases and pig seropositivity were recorded. A good correlation was observed between mosquito number and JEV positivity in pigs/human, and between pigs and human cases (p < 0.05). Human population in Sivasagar was at higher risk for JE infection (OR: 6.46, p < 0.0001) than in Kamrup rural district. Interpretation & conclusion: This study indicates that a seasonal correlation exists between mosquito abundance and JEV seroconversion in pigs with concurrent human JEV outbreaks under field conditions in Sivasagar and Kamrup rural districts of Assam and that monitoring mosquito abundance/density and pig JEV seropositivity may help in predicting JEV outbreak in human population in the region