Malaria Vector Bionomics: Countrywide Surveillance Study on Implications for Malaria Elimination in India (Preprint)

Abstract

BACKGROUND Mosquito vectors exhibit variable biological characteristics that influence their response to vector control measures. Therefore, updated information on vector bionomics is important for ensuring that the currently used vector control strategies and tools are effective in view of the goal of malaria elimination in India by 2030. OBJECTIVE The objectives of the study were to assess the indoor and outdoor resting proportions of vector species, to know the host biting/feeding preference of vector species, the sites of transmission, and to get the susceptibility status of vectors agisnt insecticides used in public health programme. METHODS Mosquito collections were made from 13 districts from eight Indian states during 2017 to 2020 using different methods to deduce their densities. After morphological identification in the field, sibling species of Anopheles mosquitoes were molecularly identified using polymerase chain reaction (PCR) specific alleles. Plasmodium falciparum and Plasmodium vivax infections in the vectors were detected out using ELISA and PCR assays. Susceptibility status of the known primary malaria vectors to the insecticides commonly used in the national programme was determined using World Health Organization (WHO) protocol. RESULTS Anopheles culicifacies, one of the primary malaria vectors, was collected (man hour density 3.1-15.9) from all the states of India except the states in the northeastern region. An. fluviatilis, another primary vector, was collected from Madhya Pradesh, Maharashtra, Karnataka and Odisha states. An. culicifacies sibling species A was predominant in Haryana and Karnataka, while species C and E were predominant in Madhya Pradesh and Maharashtra. An. culicifacies was mainly endophilic in all the states except Madhya Pradesh where proportion of semigravid and gravid mosquitoes was nearly half of the unfed mosquitoes. Human blood index of An. culicifacies varied from 0.001 to 0.220 in all the study sites. The sporozoite rate of An. culicifacies was in the range of 0.06 – 4.24 except in Madhya Pradesh, where none of the vector mosquitoes was found infected with Plasmodium parasite. In the study area, An. culicifacies was resistant to DDT (<39% mortality). It has developed resistance also to malathion (49-78% mortality) in all districts except in Angul, Odisha and Palwal, Haryana and to deltamethrin in districts of Maharashtra, Gujarat, Haryana, and Karnataka states. CONCLUSIONS Our study provides crucial information on prevalence, resting behavior and sibling species composition of malaria vectors in India. It is evident from the study that development of resistance in An. culicifacies, the primary vector, to synthetic pyrethroids is increasing in the country. Result of the study also indicated towards the change in the resting behavior of An. culicifacies in Madhya Pradesh but needs larger studies to reaffirm this plausible change. Our findings will be crucial in developing vector control strategies in India, which intends to eliminate malaria by 2030.