Natural transmission of dengue virus serotype 3 by Aedes albopictus (Skuse) during an outbreak in Havelock Island: Entomological characteristics

• Among the three Aedes spp., Aedes albopictus was predominant.
• A. albopictus infestation levels were higher than A. aegypti in Havelock island.
• Two pools, of A. albopictus mosquitoes, were found positive for type 3 DENV.
• A. albopictus was identified as the primary vector which was responsible for the outbreak of dengue.
• Havelock Island appears to be a new focus of dengue transmission.

From May to June 2014, an outbreak of dengue virus (DENV) illness occurred in the Havelock Island, South Andaman. Entomological investigations were undertaken during the peak of the outbreak, from 26th May–4th June, to identify the primary vector(s) involved in the transmission so that appropriate public health measures could be implemented. Adult mosquitoes were collected by BG-Sentinel traps in houses and neighborhoods of clinically ill patients. Water holding containers were inspected for the presence of mosquito larvae and pupae. Adult mosquitoes were analyzed by RT-PCR for the presence of nucleic acids of DENV and CHIKV. A total of 498 mosquitoes were collected and processed in 27 pools. The species composition comprised of 58.3% Aedes albopictus, 7.5% Aedes aegypti and 4.2% Aedes edwardsi and 3.1% constituted others. Two A. albopictus pools were found to be positive for DENV RNA. Sequencing of the RT PCR 511 base pair amplicon positive samples showed homology with DENV-3, suggesting that serotype-3 was responsible for the outbreak and A. albopictus was the primary vector responsible. This was supported by high container (10.1%), premise (25.4%) and Breteau (27.9) indices, with miscellaneous receptacles (2.4%), tree holes (1.2%) and discarded tires (1.2%) registering relatively higher container indices. This is the first report of detection of DENV in A. albopictus from Andaman and Nicobar Islands.

• Dengue fever is an emerging public health problem in the Union Territory of Andaman and Nicobar Islands.
• Competent vectors occur in high densities in the Islands.
• An increase in the number of patients with dengue like febrile illness was observed in Havelock, a popular tourist destination.Figure optionsDownload as PowerPoint slide