Detection of dengue viruses in vector mosquitoes collected from localities with reported dengue cases in the Gampaha District, 2008-2009

Abstract

Dengue is an important mosquito-borne flaviviral infection in Sri Lanka. Aedes aegypti is considered as the predominant vector of dengue and Ae. albopictus is considered as a subsidiary vector of dengue in Sri Lanka. Detection of dengue virus in these two vector species is important for control activities. Objective of this study was to examine transmission of dengue viruses by Ae. aegypti and Ae. albopictus mosquitoes in the field. Hundred dengue patients confirmed by both clinically and serologically were selected. Mosquito surveillance was conducted by visiting patient's premise within one week of notification of a case. A buffer zone covering 500 m radius in each confirmed patient's premise was surveyed. Larvae and adults were collected using standard larval surveillance techniques and a back-pack aspirator respectively. Adult and larvae were pooled (1-50 larvae/adult per pool). Single step single tube R -PCR assay followed by Semi-Nested-PCR agarose gel electrophoresis was performed. Ethical permission for this study was obtained from the Ethical Review Committee of the Faculty of Medicine, University of Kelaniya. Informed written consent was obtained from each patient for conducting mosquito surveillance at his/her premise. From 100 confirmed dengue case reported stations, 10% (10/100) and 60% (60/100) pools of Ae. aegypti and Ae. albopictus larvae were collected respectively. Adult mosquito collection showed 8% (8/100) and 30% (30/100) of Ae. aegypti andAe.albopictus respectively. These results showed high density of Ae. albopictus mosquitoes. Dengue 3 viral infection was detected in 1 and 7 pools of Ae. aegypti and Ae. albopictus respectively. Transmission of dengue serotype 3 virus by Ae. albopictus and high density of this species in selected areas were observed. Although Ae. aegypti is still the main vector initiating outbreaks and transmitting the disease in city centers, the possibility of Ae. albopictus playing a major role in this region should not be ignored.Theseadultmosquitoes may acquire dengue viruses through horizontal or vertical transmission. Alargenumber of mosquito pools needed to test for confirmation.Acknowledgements: Financial assistance from the WHO/SEARO (WHO/SEARO SN1167)and technical assistance from the IAEA (IAEA TC SRL TC 5/042) are gratefullyacknowledged.