Vectors of Japanese Encephalitis in India

In India, the Japanese Encephalitis (JE) virus has been isolated from 17 mosquito species, with the highest occurrence in the Culex vishnui subgroup, including Cx. tritaeniorhynchus, Cx. vishnui, Cx. quinquefasciatus and Cx. pseudovishnui. Female mosquitoes acquire infection after feeding on infected vertebrate hosts and, following an extrinsic incubation period of 9–12 days, become capable of transmitting the virus to humans and other hosts. These vectors are widespread and predominantly breed in water bodies with abundant vegetation such as paddy fields, irrigation canals, puddles, shallow ditches, and fishponds, which explains their high prevalence in rural areas. JE vectors are crepuscular, being most active during dawn and dusk, and are primarily exophagic, feeding outdoors, though they may occasionally feed or rest indoors. Cx. tritaeniorhynchus, the principal vector, is mainly exophilic but may exhibit indoor resting during periods of high density, particularly during paddy cultivation. The vectors are largely zoophilic, preferring to feed on cattle and pigs, with cattle potentially providing a protective zooprophylactic effect by diverting mosquito bites away from humans. Their population peaks during the monsoon and post-monsoon seasons (July to December). Feeding activity is highest during the first hour after sunset, mostly outdoors, although entry into houses and animal shelters at night has been observed. The flight range of the Cx. vishnui group typically varies from 1 to 3.5 kilometres, depending on environmental conditions, availability of hosts, and breeding habitats.