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

BACKGROUND & OBJECTIVE: 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.

A long-term study on vector abundance & seasonal prevalence in relation to the occurrence of Japanese encephalitis in Gorakhpur district, Uttar Pradesh.

BACKGROUND & OBJECTIVES: Japanese encephalitis (JE) virus is an important cause of viral encephalitis in Gorakhpur district, UP. The area has been experiencing outbreaks of JE since 1978. No in-depth longitudinal studies have been carried out on the mosquito species, particularly JE vectors prevailing in the area. Entomological studies were carried out in the district in order to determine the species composition, relative abundance and seasonal prevalence of mosquitoes in relation to the incidence of JE. METHODS: Three JE affected villages were selected as study sites. Weekly visits were made to each village and mosquito collections were made in and around the pig enclosures and cattle sheds with the help of mouth aspirators, aided by flash lights at dusk. RESULTS: The overall mosquito population showed a bimodal pattern with short and tall peaks during March and September respectively. Based on the elevated density and infection with JE virus, Culex tritaeniorhynchus has been considered responsible for causing epidemics in the area. Cx. pseudovishnui, Cx. whitmorei, Cx. gelidus, Cx. epidesmus, Anopheles subpictus, An. peditaeniatus and Mansonia uniformis are suspected to have played some role in the epidemiology of JE in the region. JE cases were reported between August and November with the peak in October when the vectors population, particularly Cx. tritaeniorhynchus was on the decline. INTERPRETATION & CONCLUSION: The results of the study indicate that Cx. tritaeniorhynchus, the most likely vector of JE together with other known vector species remained more active during the period of paddy cultivation. Integrated antilarval measures before the beginning of paddy irrigation may check the breeding of JE vectors in the paddy fields. It may prove beneficial in reducing the vector population during the JE transmission season.

First isolation of Japanese encephalitis virus from the mosquito, Culex tritaeniorhynchus Giles, 1901 (Diptera: Culicidae) in Gorakhpur district, Uttar Pradesh.

A strain of Japanese encephalitis (JE) virus has been isolated from a pool of female mosquitoes of C. tritaeniorhynchus, using C. bitaeniorhynchus cell line. This is the first report of JE virus isolation from mosquitoes in Gorakhpur district of Uttar Pradesh, north India.