Entomological investigation on malaria vector studies in earlier conflict areas of Sri Lanka after 30 years

Abstract

Entomological investigations on the abundance of malaria vector mosquitoes have not been studied in northern and eastern parts of the Sri Lanka over the past 30 years due to the separatist war. The main aim of this study was to explore diversity and abundance of Anopheles mosquitoes in earlier conflict areas in Sri Lanka.

Monthly entomological monitoring was carried out at 60 possible malaria sensitive localities situated approximately 12 km apart in 15 selected sentinel sites in Ampara (4), Batticaloa (3), Mannar (3) and Trincomalee (5) districts for 32 months (June 2010 to August 2013). Adult mosquitoes were collected by WHO recommended techniques.

Out of 701,356 anophelines collected, 𝘈𝘯. 𝘤𝘶𝘭𝘪𝘤𝘪𝘧𝘢𝘤𝘪𝘦𝘴 was noted only in Ampara, Batticaloa and Trincomalee Districts. Although the main vector 𝘈𝘯. 𝘤𝘶𝘭𝘪𝘤𝘪𝘧𝘢𝘤𝘪𝘦𝘴 (n= 1,876) was low in numbers, the presence of secondary vectors including 𝘈𝘯. 𝘴𝘶𝘣𝘱𝘪𝘤𝘵𝘶𝘴 (n= 205,594) were high in these areas. 𝘈𝘯. 𝘯𝘪𝘨𝘦𝘳𝘳𝘪𝘮𝘶𝘴 (n= 227,057), 𝘈𝘯. 𝘣𝘢𝘳𝘣𝘪𝘳𝘰𝘴𝘵𝘳𝘪𝘴 (n= 35,150), 𝘈𝘯. 𝘷𝘢𝘨𝘶𝘴 (n= 21,161), 𝘈𝘯. 𝘱𝘢𝘭𝘭𝘪𝘥𝘶𝘴 (n= 17,403), 𝘈𝘯. 𝘢𝘯𝘯𝘶𝘭𝘢𝘳𝘪𝘴 (n= 4,882), 𝘈𝘯. 𝘷𝘢𝘳𝘶𝘯𝘢 (n= 3151), 𝘈𝘯. 𝘵𝘦𝘴𝘴𝘦𝘭𝘭𝘢𝘵𝘶𝘴 (n= 718) and 𝘈𝘯. 𝘢𝘤𝘰𝘯𝘪𝘵𝘶𝘴 (n= 591) were the other species reported. There was a change in breeding habitats of 𝘈𝘯. 𝘤𝘶𝘭𝘪𝘤𝘪𝘧𝘢𝘤𝘪𝘦𝘴 and 𝘈𝘯. 𝘴𝘶𝘣𝘱𝘪𝘤𝘵𝘶𝘴. They were found more conducive to breeding in built wells, brackish water habitats and waste water collections which were below 3 mg/l of dissolved oxygen (2.85 ± 0.03). These results indicate that particularly 𝘈𝘯. 𝘤𝘶𝘭𝘪𝘤𝘪𝘧𝘢𝘤𝘪𝘦𝘴 has adapted to breed in wide range of water bodies including waste water collections although they were earlier considered to breed in clean and clear water with high dissolved oxygen. The adaptation of the major and subsidiary vector mosquitoes to widespread water bodies (along with increase in imported cases) could be a potential factor for the increase in the incidence of malaria in the future even though reported cases are low at present. Further, entomological surveillance detected the presence of 𝘈𝘯. 𝘫𝘦𝘺𝘱𝘰𝘳𝘪𝘦𝘯𝘴𝘪𝘴 from the country after 106 years. Hence, more classical entomological studies are required to describe species currently found in the country; revision of morphological identification keys is a step in this direction.