Distribution of dengue virus types in Aedes aegypti in dengue endemic districts of Rajasthan, India.

BACKGROUND & OBJECTIVE Dengue haemorrhagic fever (DHF) is the major cause of sustained morbidity/ mortality among human cases of dengue in dengue endemic areas of Rajasthan. Screening of mosquitoes collected from disease endemic settings and typing the virus could provide significant epidemiological information for prospective risk of DHF. We therefore carried out a study on different dengue virus types as occurring in field collected Aedes aegypti mosquitoes from four dengue endemic districts of Rajasthan, India. METHODS Adult Ae. aegypti were collected from the human dwellings of urban, peri-urban and rural settings of four dengue endemic districts of Rajasthan, India. The field collected adults were fed on 4 per cent glucose solution and kept in the laboratory for 3-4 days. The adult field collected Ae. aegypti, were subjected to indirect fluorescence antibody test (IFAT) following standard procedure. Commercially acquired monoclonal antibodies against DEN types 1, 2, 3 and 4 were used. The remnants of IFA test subjected mosquitoes were made into viral suspension which was inoculated into the cell culture medium and mouse brain to confirm the presence of virus as shown by IFA test. RESULTS Of the 498 adult Ae. aegypti tested, 78 (15.6%) were positive by IFA test. Among urban areas, desert area (Jodhpur) showed highest (21.6%) mosquito infectivity followed by 7.1 per cent in forest and river area (Kota) and least (3.2%) in semi-arid area (Jaipur). Among rural settings also, desert area showed maximum (25.0%) natural infection in mosquitoes followed by rural setting-1 of semi-arid area (24.1%). Among urban setting of desert area, all the four dengue types viz., DEN-1, 2, 3 and 4 were detected. In semi-arid area, urban settings showed presence of DEN-3, whereas among rural settings, rural-1 showed all the four DEN types, rural-2 showed DEN-1 and DEN-3, rural-4 showed DEN-3 and DEN-4, and rural-3 showed no mosquito infections. In forest and river area, among urban settings only, three DEN types, 1, 2 and 4 were observed. INTERPRETATION & CONCLUSION In desert and semi-arid areas of Rajasthan, where people possess tendency of over- and sustained storage of domestic water, present observations on occurrence of all four dengue virus types may have important bearing on the epidemiology of DHF in the area.