Seasonal variations of dengue vector mosquitoes in rural settings of Thiruvarur district in Tamil Nadu, India

Background & objectives: Mosquitoes are vectors of several important vector-borne diseases (VBDs) like malaria, dengue, chikungunya, Japanese encephalitis (JE) and lymphatic filariasis (LF). Globally, these VBDs are of major public health concern including India. The information on vector mosquitoes from Thiruvarur district in Tamil Nadu state remains largely either unknown or undocumented. The present study was, therefore, undertaken to find out the seasonal variation in mosquitoes with special reference to dengue vectors in rural areas of Thiruvarur district, Tamil Nadu, India. Methods: Surveillance of immature vector mosquitoes was undertaken from March 2018 to February 2019. The emerged adults were identified to find out the composition of mosquito species prevalent in the district. The seasonal variations of the mosquitoes especially dengue vectors were analysed for summer (March-July) spring (August-November) and winter (December-February) seasons in all the blocks of Thiruvarur district. Results: A total of 4879 mosquitoes emerged from the immature collection and the species identification revealed the prevalence of both vector and non-vector species. Five important mosquito vectors collected were -Aedes albopictus, Ae. aegypti, Culex tritaeniorhynchus, Cx. gelidus, and Cx. quinquefasciatus. Other mosquito species collected were Lutzia fuscana, Anopheles barbirostris, An. subpictus, and Armigeres (Armigeres) subalbatus. During the spring season, the dengue vectors showed high indices of breateau index (BI), ranging from 16 to 120; besides, container index (CI) ranging from14.29 to 68.57 and pupal index (PI) from 53.33 to 295 among the study blocks. The major breeding sites were discarded plastic containers, discarded tyres, open sintex tanks (water storage tanks), cement tanks, discarded fibre box, pleated plastic sheets, tree holes, bamboo cut stumps, coconut spathe, and coconut shells. Interpretation & conclusion: The immature vector surveillance revealed seasonal variations in the entomological indices of Aedes breeding potential. The high indices observed indicate high Aedes breeding density and, therefore, a higher risk for dengue/chikungunya outbreaks in rural areas of Thiruvarur district. The present finding warrants intensive surveillance and follow up vector control measures to avert outbreaks and prevent vector-borne diseases. Health education and the community participation in awareness camps prior to monsoon and societal commitment will help in strengthening source reduction, anti-larval operations and anti-adult measures to tackle vector-borne diseases especially dengue.