Characterization of the anopheline vector breeding habitats: Implications for elimination of malaria in tribal inhabited Car Nicobar Island.

Background & Objectives: Malaria is an important public health problem in Andaman & Nicobar archipelago. Among the three districts, Nicobar is the most endemic district where API is >2. In this district, the malaria incidence in Car Nicobar Tehsil has declined steadily over the past 10 years. A renewed initiative to consolidate this gain is being made with the ultimate objective of achieving zero indigenous transmission of malaria in Car Nicobar. So, the present study undertook a close environmental monitoring of water bodies for assessing changes in the risk potential of mosquito vector breeding habitats which can augment the elimination programme.

Methods: The breeding habitats of anopheline mosquitoes were sampled in 16 areas of Car Nicobar Island for eight time periods during 2017-2020. Along with anophelines, various associated water parameters (n=60) were estimated, viz. physicochemical (n=13), and biological, which included culicine mosquito immatures, insect predators (n=5), phytoplanktons (n=31) and zooplanktons (n=10).

Results: In the 16 study sites, overall 1126 surface water stagnating bodies constituting 21 different habitat types were surveyed. Of these, 17 were positive for anopheline breeding. Water bodies from three villages were consistently found to be positive for anopheline breeding. However, early instars of anopheline larvae were more abundant compared to the late instars. Four anopheline species were recorded, including Anopheles sundaicus, A. barbirostris, A. insulaeflorum and A. subpictus, in which 48 per cent were A. sundaicus. Multivariable analysis indicated that anopheline density was significantly higher in permanent water bodies than in temporary habitats (P<0.05) (high risk of anophelines). The highest pH (≥8.2), dissolved solids (≥0.39) levels showed significantly (P<0.05) decreased larval densities (lower risk of breeding), adjusted with breeding sites and season. Nitrite levels increased (P=0.022) larval densities.

Interpretation & Conclusions: The present study facilitated estimating the productive period of a larval habitat enabling target larval sources to reduce adult populations. Implementing larviciding strategy before monsoon season is presumably the most cost-effective strategy. The output can be utilized for environmental monitoring of mosquito breeding risk in other malaria endemic areas, particularly where medium/large water bodies are the predominant breeding sites for malaria vectors.