An Entomological study to plan intervention for prevention of dengue in Gampaha district, Sri Lanka

Abstract

BACKGROUND: Dengue is the most common and fastest spreading human arbo viral disease worldwide. Most control efforts are based not on insecticides but on suppression of vectors by reducing the number of larval breeding habitats. METHODS: Total of 2000 houses in the District of Gampaha in the Western Province which had the second highest transmission of dengue in 2006 was selected using grid sampling technique, based on disease incidences during 2003—2006. Mosquito surveillance was carried out from 0900 hrs to 1400 hrs during June-August, 2007. Larval and pupal surveillances were carried out indoors and outdoors using standard larval surveillance techniques. RESULTS: The House, Container and Breteau indices for Aedes larvae were 49.3%, 26.1% and 26.9% respectively. The common breeding places for Aedes species were discarded containers 27.1% (559/2064), unused bowls 16.2% (334/2064), plant axils 11.7% (242/2064), water storing barrels 11.4% (236/2064) and coconut shells 5.4%(111/2064). Most productive container types for larvae were tyres (44.3%), plant axils (37.6%), ceramic jars (36.6%), discarded containers (29.5%) and fish tanks (25.0%). Most productive container types for pupae were discarded containers (13.4%), fish tanks (10.4%), unused bowls (8.38%), ceramic jars (7.31%) and coconut shells (6.3%). Aedes albopictus (larvae-85.3%, pupae-80.4%) was the most predominant vector in the district. Earthen pots, plant axils, discarded containers and buckets were the main sources for Aedes albopictus while tyres, barrels, tanks and bowls were for Aedes aegypti. Further, mixed breeding was observed in water storage containers and tyres. CONCLUSION: Discarded small bowls/containers were the key containers with the highest pupal index. Natural breeding habitats such plant axils may also significantly contribute to pupal production. Therefore an integrated control effort to include community level awareness programmes, improved solid waste management for small containers and efforts to prevent breeding in plants is suggested for prevention of dengue in the district. © 2008 Elsevier Inc.