Ecological study on mosquito vectors of Japanese encephalitis virus in Bellary district, Karnataka

Background & objectives: Japanese encephalitis virus (JEV) has been a serious public health problem in Bellary district since 1981. Though JE is a vector borne disease, no published record was available regarding prevalence of mosquito species in this region. A two years ecological study was therefore conducted to determine species composition, seasonal prevalence and relative abundance of culicid taxa, particularly JE vectors endemic to this area. Methods: Three villages with recent JE out breaks, were selected for regular mosquito collections. During daytime, adult mosquitoes resting inside human and domestic animal habitations were collected using aspirators and flashlights at weekly intervals. Similarly, adult mosquitoes were collected from cattle sheds and pig enclosures at dusk hours. Results: A total of 120113 mosquitoes collected at dusk belonged to 5 genera and 24 species, including 13 species those have already yielded JE virus in India with Cx. tritaeniorhynchus contributing to 70.3 per cent. General mosquito population showed bimodal pattern of peak occurrence during February and October in both the peaks, Cx. tritaeniorhynchus contributed maximum JE. Substantial densities of An. subpictus and An. peditaeniatus during JE season suggest the supportive role of these species. Other vector species viz., Cx. quinquefasciatus, Cx. pseudovishnui, Cx. vishnui, Cx. gelidus, Cx. fuscocephala, Cx. bitaeniorhynchus, Ma. annulifera, Ma. uniformis and An. barbirostris perhaps have a limited role in the transmission of JE virus due to their extremely poor density. Interpretation & conclusion: Cx. tritaenorhynchus appears to have a major role in the transmission of JE virus in Bellary district. Risk of transmission of JEV to humans can be reduced by house spraying with residual insecticides and intermittent paddy irrigation.