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.

A preliminary study of multilevel geographic distribution & prevalence of Aedes aegypti (Diptera: Culicidae) in the state of Goa, India.

BACKGROUND & OBJECTIVES: Dengue virus activity has never been reported in the state of Goa. The present study was carried out to document a multilevel geographic distribution, prevalence and preliminary analysis of risk factors for the invasions of Aedes aegypti in Goa. METHODS: A geographic information system (GIS) based Ae. aegypti surveys were conducted in dry (April 2002) and wet (July 2002) seasons in the rural and urban settlements. The random walk method was used for household coverage. The non-residential area visits included ancillaries of roadways, railways, air-and seaports. Simultaneous adult mosquito collections and one-larva per container technique were adopted. RESULTS: The Ae. aegypti larval and adult prevalence was noted in all the four urban areas in both dry (Density index (DI)= 3 to 6) and wet (DI= 5 to 7) seasons and only one out of 3 villages showed Ae aegypti presence in wet season (DI= 5 to 7). In the residential areas, hutments showed higher relative prevalence indices (Breteau index, BI=100; container index, CI=11.95; adult house index, AHI=13.33) followed by close set cement houses (BI=44.1; CI=12.0; AHI=11.24). Ae aegypti relative prevalence indices were also more for households with pets (BI=85.11; CI=12.5; AHI= 42.85); those with tap had higher risk (larval house index, LHI =32.03; relative risk, RR>2, n=256). Plastic drum was the most preferred breeding place (chi(2) = 19.81; P<0.01; RR=3.41) among domestic containers and rubber tyres (chi(2) = 11.86; P<0.01; RR=3.61)among sundry/rainfilled containers. INTERPRETATION & CONCLUSION: Established Ae aegypti prevalence in the urban settlements during dry and wet seasons and its scattered distribution in a rural settlement spell risk of dengue infection at macro-level. In the residential areas nature and types of the households, tap water supply and storage and communities' attitude and practices contribute to sustained meso-level risk of Ae aegypti prevalence dependant DEN. The non-residential areas offer transient meso-level risk as Ae aegypti prevalence was seasonally unstable and monsoon dependent. Risk at micro-level was due to the preferred larval habitats of Ae aegypti breeding viz., residential plastic-ware and tyres, and transport tyres in non-residential areas.

Activity of dengue-2 virus and prevalence of Aedes aegypti in the Chirimiri colliery area, Madhya Pradesh, India.

Repeated outbreaks of a suspected viral fever in Chirimiri colliery area, Madhya Pradesh were reported since 1990. The area consists of an agglomeration of sprawling settlements at varying altitudes of 816 to 890 m and it has partial sylvan cover. During a 1992 outbreak 25 patients' sera were tested, of which 13 showed seropositivity to dengue (DEN) by MAC-ELISA test; DEN-2 was isolated from Aedes aegypti collected from two of the eight settlements of the area. The principal vector, Ae. aegypti, was prevalent in all the settlements studied; Breteau indices (BI) varied between 2.5 and 125.0; adult house indices (AHI) between 0 and 60.0%; Ae. albopictus and Ae. vittatus occurred in considerable numbers; Ae. aegypti bred in more containers with nonpotable water than those with potable water; the breeding of this species was noted in a maximum number of cement tanks while mud pots were predominant among the available containers. Paired comparisons between relative prevalence indices showed significant correlation and regression coefficients. Significant association of Ae. aegypti breeding with the households having tap water supply was noted, the relative risk declining with the people's use of well water either exclusively or in combination with other sources of water supply. It was also collected in the nonresidential areas. The role of ecological factors in the maintenance and spread of Ae. aegypti and dengue in these settlements is discussed.

Dengue in Gujarat state, India during 1988 & 1989.

Following the reports of epidemics of febrile illness from several rural and urban areas of Gujarat state (India) in 1988, epidemiological investigations were carried out and dengue (DEN) virus activity was demonstrated in large cities such as Surat and Rajkot as well as several villages in Sabarkantha district. Two strains of dengue type-2 each were isolated from human sera from Surat city and a village in Sabarkantha district. Six strains of dengue virus were isolated from Aedes aegypti mosquitoes collected at Chotasan village, two of which were confirmed as DEN type-2. Of the 560 patients' sera tested from different areas (including villages and townships), 122 showed evidence of dengue infection and another 236 showed a broader reaction with flaviviruses. Entomological investigations showed a widespread distribution of Ae. aegypti both in urban and rural areas. In the household conditions this mosquito was found to breed predominantly in containers with non-potable water. Amongst these, cement containers manufactured in towns and distributed to the villages seem to play an important role in the spread of this species. In non-residential areas prolific breeding of Ae. aegypti was observed in automobile tyre dumps, and varied types of scrap, in towns and villages. Distribution and relative prevalence of the species were studied in 46 towns and villages, covering the spectrum of rural-urban-continuum. These studies provide an indication regarding the mechanism of the spread of DEN virus through peoples' movement, transport, the process of urbanisation etc.

Insecticide susceptibility status of certain populations of Aedes aegypti mosquito from rural areas of Maharashtra state.

Ae. aegypti mosquitoes from rural areas of Maharashtra state were subjected to insecticide bio-assays. All the populations showed resistance to DDT at larval and adult stages. No resistance to deltamithrin and malathion was detected at any stage. Biochemical analysis of these mosquito populations showed that resistance to DDT was probably due to increase in the kinetics of glutathione S-transferase.

Entomological investigations during outbreaks of dengue fever in certain villages in Maharashtra state.

Outbreaks of dengue (DEN) fever are reported from 22 villages in five districts in the state of Maharashtra. DEN viral antigen was detected by indirect immunofluorescence test in 34 of 375 female Aedes aegypti mosquitoes collected from 8 villages. DEN types 2 and 3 were identified among the 16 strains that were isolated. None of the 64 male mosquitoes showed the presence of viral antigen; 281 males and 323 females reared from field collected larvae were also found negative. Indoor spraying of DDT in the affected villages produced a drastic reduction in Ae. aegypti catches. No viral antigen was detected in mosquitoes caught subsequent to the spray. With the introduction of water supply through taps, which is often inadequate, people are compelled to store water for domestic purposes, which favours an increase in Ae. aegypti breeding. In view of changing rural ecology associated with the development process, continued surveillance of the spread of Ae. aegypti as well as the diseases borne by this vector are recommended.