West Nile virus: the Indian scenario

Abstract

West Nile virus (WNV) is an important arthropod borne flavivirus; usually causes a mild infection called West Nile fever (WNF) in human and horses. Mosquitoes are the principal vectors of WNV. Various Culex species are found to act as vectors in different geographical regions. The virus is maintained in a bird-mosquito cycle in nature. In India, Culex mosquitoes are tentatively incriminated as vectors of WNV. Experimental studies have shown that Culex tritaeniorhynchus, Cx. vishnui, Cx. bitaeniorhynchus and Cx. univittatus, Culex pipiens fatigans and Aedes albopictus could act as potential vectors of WNV. Transovarial transmission of WNV has been experimentally demonstrated in Culex mosquitoes. Apart from mosquitoes, the role of other arthropods is also considered in the maintenance of WNV during inter-enzootic periods. The possible role of ardeid birds in the maintenance of WNV has been described in India. Though very few clinically overt cases of human encephalitis due to WNV are observed, Japanese encephalitis virus (JEV) is found to dominate in southern India. WNF in horses has not been documented in India. JEV immunized monkeys were protected from WNV challenge and the WNV immunization was found to reduce the disease severity due to JEV. Based on the limited genome sequence analysis, the Indian isolates are grouped together under the genetic lineage-I. WNV infection is diagnosed by IgM antibody capture enzyme linked immunosorbant assay, haemagglutination inhibition test, neutralization test and reverse transcriptase-polymerase chain reaction (RT-PCR). For the effective control of Culex mosquitoes, integrated vector control strategies are recommended. Specific methods are not available for the treatment of WNV infection. However, in patients with encephalitis supportive therapy is recommended. Though a few candidate vaccines are under laboratory trial, no vaccine has been available commercially for the control of WNV infection in human and animals. In view of the global interest on WNV, this paper describes the present status of WNV in India.