Spread, establishment & prevalence of dengue vector Aedes aegypti (L.) in Konkan region, Maharashtra, India.

BACKGROUND & OBJECTIVE Aedes aegypti (L.) (Diptera: Culicidae) was surveyed in the residential biotopes of Sindhudurg, Ratnagiri and Raigadh districts, Maharashtra State during dry (January-May & November- December) and wet (June-October) months in 2002 to update information on its distribution, to analyse post invasion establishment, and to study its prevalence. METHODS The survey was designed to unfold Ae. aegypti distributions at landscape, habitat and micro-habitat levels. Risks of distribution and establishment due to differences amongst settlements, households and habitat attributes were analysed by univariate and multivariate methods. Demographic/transport changes were surveyed for its breeding refugia during dry months and prevalence during the wet seasons. Chi square tests for difference and relative risks of container types were applied to assess container habitats preferences for Ae. aegypti breeding, thus contributing to the risk of establishment and prevalence through seasons. RESULTS Ae. aegypti was present in 16 out of total 28 settlements in dry season and 22 of 25 in wet season; the Breteau index (BI) varied from 1.25 to 57.33 and the container index (CI) was 0.6 to 25.81 in the dry season and BI from 1.25 to 110-00 and CI - 0.2 to 11.37 in the wet season, respectively. At macro-level, rural settlements and ports showed higher odds ratios (OR>1) for presence of Ae. aegypti. At meso-level, OR were 65.8, 24.8 and 4.9 for Ae. aegypti breeding in compact houses, clustered housing and in houses with tap water source respectively. At micro-level the plastic drums and small plastic containers were the important key habitats of its breeding. In the non-residential areas Ae. aegypti breeding was noted in one port during dry season; 10-road transport tyre dumps and scrap, 5 of 7 seaports and none of the two railway station areas during wet season. INTERPRETATION & CONCLUSION At macro-geographic level Ae. aegypti distribution increased in 3 settlements, new establishment was seen in 7, new records in ten settlements and two were negative in past and present surveys. Logistic regression analyses indicated that the distribution was found to be more associated with ports and rural areas. At meso-geographic level the house aggregations and household drinking water supplies were of risk even at lower urbanization and rural levels. At micro-level, the site and potability were confounders; outdoor non potable water storage containers posed significant breeding risk, the potable water storage was significant but it contributed little to Ae. aegypti breeding. Further, Ae. aegypti breeding showed high preference to the plastic drums and other plastic miscellany. The results signified an expansion in the risk area of diseases borne by it in the context of urbanization, transport development and changing habitats.