Dengue vectors in urban and suburban Assam, India: entomological observations

ABSTRACT

Background: Dengue is rapidly becoming established in north-east India andspreading, on account of rapid urbanization and population movement, withreported morbidity and attributable death cases. This study aims to determine theseasonal abundance of Aedes (Stegomyia) albopictus and Aedes (Stegomyia)aegypti in Guwahati metropolis and suburban settlements; to characterize thebreeding resources for these mosquitoes; and to ascertain the status of theirsusceptibility to adulticides and larvicides.Methods: Mosquito larval surveys were carried out in different localities in bothGuwahati city and adjoining suburbs from January to December 2013, to determinethe seasonal abundance of disease vectors and their breeding preferences.The insecticide susceptibility status of mosquito adults and larval populations ofboth Aedes aegypti and Aedes albopictus was ascertained, using World HealthOrganization standard diagnostic concentrations and test procedures.Results: The study revealed that both Aedes aegypti and Aedes albopictus arewidely abundant in Guwahati city and suburbs, and breeding in a wide variety ofresources. Aedes albopictus, however, was the predominant mosquito speciesin suburbs, breeding preferentially in flower vases, cut-bamboo stumps and leafaxils. Aedes aegypti was the most common in the city, breeding predominantly indiscarded tyres, cement tanks and used battery boxes. Both Aedes aegypti andAedes albopictus were resistant to dichlorodiphenyltrichloroethane (DDT; 4%), butsusceptible to malathion (5%), and exhibited a varied response to pyrethroids.However, larval populations of both these mosquito species were susceptible tolarvicides, including malathion (1.0 mg/L), temephos (0.02 mg/L) and fenthion(0.05 mg/L), at much lower dosages than diagnostic concentrations.Conclusion: Given the seasonal abundance and case incidence in city areas,it is highly probable that Aedes aegypti is the predominant mosquito vectortransmitting dengue virus. The study results have direct relevance for the statedengue-control programme, for targeting interventions and averting outbreaks andspread of disease