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.