Dengue vectors in urban and suburban Assam, India: entomological observations.
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Date
2014-01
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WHO Regional Office for South-East Asia
Abstract
Background: Dengue is rapidly becoming established in north-east India and
spreading, on account of rapid urbanization and population movement, with
reported morbidity and attributable death cases. This study aims to determine the
seasonal abundance of Aedes (Stegomyia) albopictus and Aedes (Stegomyia)
aegypti in Guwahati metropolis and suburban settlements; to characterize the
breeding resources for these mosquitoes; and to ascertain the status of their
susceptibility to adulticides and larvicides.
Methods: Mosquito larval surveys were carried out in different localities in both
Guwahati city and adjoining suburbs from January to December 2013, to determine
the seasonal abundance of disease vectors and their breeding preferences.
The insecticide susceptibility status of mosquito adults and larval populations of
both Aedes aegypti and Aedes albopictus was ascertained, using World Health
Organization standard diagnostic concentrations and test procedures.
Results: The study revealed that both Aedes aegypti and Aedes albopictus are
widely abundant in Guwahati city and suburbs, and breeding in a wide variety of
resources. Aedes albopictus, however, was the predominant mosquito species
in suburbs, breeding preferentially in flower vases, cut-bamboo stumps and leaf
axils. Aedes aegypti was the most common in the city, breeding predominantly in
discarded tyres, cement tanks and used battery boxes. Both Aedes aegypti and
Aedes albopictus were resistant to dichlorodiphenyltrichloroethane (DDT; 4%), but
susceptible to malathion (5%), and exhibited a varied response to pyrethroids.
However, larval populations of both these mosquito species were susceptible to
larvicides, 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 vector
transmitting dengue virus. The study results have direct relevance for the state
dengue-control programme, for targeting interventions and averting outbreaks and
spread of disease.
Description
Keywords
Aedes aegypti, Aedes albopictus, Assam, dengue, insecticide susceptibility status, mosquito breeding habitats, north-east India, seasonal abundance
Citation
WHO South-East Asia Journal of Public Health 2014;3(1): 51-59.