Sharanga Santhirasegaram

Background: Malaria was eliminated from Sri Lanka in 2013. However, the influx of infected travelers and the presence of potent anopheline vectors can re-initiate transmission in Jaffna city, which is separated by a narrow strait from the malaria-endemic Indian state of Tamil Nadu.Methods: Anopheline larvae were collected from different habitats in Jaffna city and the susceptibility of emergent adults to DDT, malathion and deltamethrin investigated.Results: Anopheline larvae were found in wells, surface-exposed drains, ponds, water puddles and water storage tanks, with many containing polluted, alkaline and brackish water.Anopheles culicifacies,An. subpictus,An. stephensiandAn. varunawere identified in the collections. Adults of the four anopheline species were resistant to DDT.Anopheles subpictusandAn. stephensiwere resistant whileAn. culicifaciesandAn. varunawere possibly resistant to deltamethrin.Anopheles stephensiwas resistant,An. subpictuspossibly resistant whileAn. varunaandAn. culicifacieswere susceptible to malathion. DNA sequencing showed a L1014F (TTA to TTC) mutation in the IIS6 transmembrane segment of the voltage-gated sodium channel protein in deltamethrin-resistantAn. subpictus—a mutation previously observed in India but not Sri Lanka.Conclusion: Anopheles subpictusin Jaffna, likeAn. stephensi, may have recently originated in coastal Tamil Nadu. Besides infected overseas travelers, wind- and boat-borne carriage ofPlasmodium-infected anophelines across the Palk Strait can potentially reintroduce malaria transmission to Jaffna city. Adaptation to diverse larval habitats and resistance to common insecticides in anophelines are identified as potential problems for vector control should this happen.

Aedes aegypti were found developing in the water in open public drains (drain-water, DW) in Jaffna city in northern Sri Lanka, a location where the arboviral diseases dengue and chikungunya are endemic. Susceptibilities to the common insecticides dichlorodiphenyltrichloroethane (DDT), malathion, propoxur, permethrin and deltamethrin and activities of the insecticide-detoxifying enzymes carboxylesterase (EST), glutathione S-transferase (GST) and monooxygenase (MO) were compared in adult Ae. aegypti developing in DW and fresh water (FW). DW Ae. aegypti were resistant to the pyrethroids deltamethrin and permethrin, while FW Ae. aegypti were susceptible to deltamethrin but possibly resistant to permethrin. Both DW and FW Ae. aegypti were resistant to DDT, malathion and propoxur. Greater pyrethroid resistance in DW Ae. aegypti was consistent with higher GST and MO activities. The results demonstrate the potential for insecticide resistance developing in Ae. aegypti adapted to DW. Urbanization in arboviral disease-endemic countries is characterized by a proliferation of open water drains and therefore the findings identify a potential new challenge to global health.