No abstract

SummaryWe conducted a 2-year (1997)(1998)(1999) longitudinal, entomological and virological study in three dengue endemic villages in Vellore district, Tamil Nadu, to understand the dynamics of dengue transmission. Aedes aegypti (Linn.), Ae. albopictus (Skuse) and Ae. vittatus (Bigot) were the prevalent vector species. Aedes aegypti was breeding throughout the year with a Breteau index ranging from 9.05 to 45.49. Aedes albopictus and Ae. vittatus were prevalent mainly in the rainy season. Small water holding containers (cemented tanks/cisterns) were the perennial breeding source of Ae. aegypti, and its abundance was significantly higher in semi-urbanized central areas than the peripheral areas of the villages. From 271 pools (4016 specimens) of adult females, eight dengue virus (DENV) isolates were obtained of which seven were from Ae. aegypti and one from Ae. albopictus. This is the first report of DENV isolation from Ae. albopictus in rural India. Infection rates in the two species were comparable. However, due to higher and perennial prevalence, Ae. aegypti is considered as primary vector with Ae. albopictus playing a secondary role. Despite circulation of all four serotypes (DENV 1-4) detected mainly during the transmission season, the high anthropophilic index of the vectors and their abundance, no human dengue case was reported, suggesting silent dengue transmission.

In the South Arcot district, an area endemic for Japanese encephalitis in Tamil Nadu, Culex tritaeniorhynchus Giles, Culex vishnui Theobald, Culex gelidus Theobald and Culex fuscocephala Theobald constituted 93.6% of 422,621 adult females representing 27 culicine species collected between August 1991 and July 1994. Vector abundance was lowest in the hot and dry season (April-June) and highest in the cool and wet season (October-December). Overall, 285,531 adult female mosquitoes (5,710 pools) were tested for virus using an enzyme-linked immunosorbent assay or by inoculation into larvae of Toxorhynchites splendens Wiedemann and identification by immunofluorescent test using JE virus specific monoclonal antibody or by both. In total, 91 isolations were made, of which 80 (88%) were identified as JE virus; 58 isolations were from Cx. tritaeniorhynchus, 22 from Cx. vishnui, 6 from Cx. fuscocephala and 5 from Cx. gelidus, giving similar minimum infection rates (MIR) of 0.28, 0.41, 0.39, and 0.52, respectively. Vector abundance and MIR increased from July concurrently with the initiation of rice cultivation. MIR peaked in September followed by a decrease in October, but mosquitoes remained abundant until March. The decrease in MIR from October onward coincided with rising herd immunity in pigs. Although MIRs in October (0.47) and November (0.42) were lower than in September (0.92), a comparable high risk of infection for humans continued because of high vector abundance and human biting rates. In the South Arcot district, the probability of a child receiving an infective bite was 0.53 per JE transmission season.

SummarySeven village units endemic for ®lariasis were assigned randomly into three arms with different intervention strategies in the years 1995 and 1996. Villages in Group A received two annual mass drug administrations (MDAs) of diethylcarbamazine (DEC) plus ivermectin (IVR