Prevalence and incrimination of Anopheles fluviatilis species S (Diptera: Culicidae) in a malaria endemic forest area of Chhattisgarh state, central India.

Background: Chhattisgarh state in central India is highly endemic for malaria and contributes about 13% of annually reported malaria cases in the country with predominance of P. falciparum. Entomological investigations were carried out in a tribal forested area of district Bastar located in the southern part of Chhattisgarh state to record the prevalence of sibling species of Anopheles fluviatilis and An. culicifacies complexes. The vector species complexes were investigated at sibling species level for their biology in terms of resting and feeding behavior and malaria transmission potential.

Methods: Indoor resting vector mosquitoes collected during 2010-2011 were identified to sibling species by cytotaxonomy and polymerase chain reaction (PCR) assay. The blood meal source analysis and incrimination studies were done at sibling species level by counter current immunoelectrophoresis and enzyme linked immunosorbent assay (ELISA) respectively.

Results: Analysis of sibling species composition revealed predominance of An. fluviatilis species S in the study area, which was found to be highly anthropophagic and rested in human dwellings whereas the sympatric species T was primarily zoophagic. Incrimination studies showed high sporozoite rate in species S, thereby confirming its vectorial efficiency. An. culicifacies was encountered in low numbers and comprised species B and C in almost equal proportion. Both these species were found to be exclusively zoophagic.

Conclusion: The observations made strongly suggest that species S of Fluviatilis Complex is the principal vector of malaria in certain forest areas of district Bastar, Chhattisgarh state and should be the target species for vector control operation. Vector control strategies based on biological characteristics of Fluviatilis S will lead to substantial decline in malaria incidence in such areas.