Mapping the Insecticide Resistance Landscape of Malaria Vectors in Odisha, India (1993-2024): A Scoping Review

Vector-borne​ diseases (VBDs) are a serious threat to public health, globally. Different genera of mosquitoes, acting as disease vectors, transmit diseases such as malaria, filariasis, dengue, chikungunya, Zika fever, and others. Malaria in humans is caused by Plasmodium species transmitted by Anopheles mosquitoes. Odisha is one of the malaria-endemic states in the country contributing to about 25% of the total (1.5-2.0 million) reported malaria cases and 30% deaths annually. Chemical insecticides and interventions have been effective in controlling vectors, and their continued usage resulted in widespread insecticide resistance in mosquito disease vectors, limiting their efficacy.

Insecticide resistance data in malaria vector species in Odisha were compiled from the published peer-reviewed literature and other validated sources by search using keywords Anopheles, anopheles species, insecticide, susceptibility, mortality, survival, insecticide resistance, Odisha, Orissa, etc. The inclusion and exclusion criteria were followed to ensure the selection of quality data published between 1993 and 2024. Data from 28 published sources were collated for compilation and adapted for this scoping review. In adult susceptibility tests, mortality rates were categorized as susceptible/resistant to the specific insecticide following the World Health Organization (WHO) criterion: susceptible: > 98% mortality; possible resistance: between 90% and 97% mortality; and confirmed resistance: < 90% mortality. Intensity bioassay data from 10 southern districts were presented for the major vector Anopheles culicifacies.

Odisha with 30 administrative districts has five defined ecotypes, coastal plains, central plateaus, central mountainous and highlands region, and western rolling and main flood plains. An. culicifacies, a major malaria vector, is reportedly prevalent in all 30 districts of Odisha, An. fluviatilis in 24 districts, An. annularis in 22, and An. minimus in two districts. An. culicifacies was the most resistant species to DDT (dichlorodiphenyltrichloroethane) (26 districts), malathion (17), and deltamethrin (10 districts). Limited data were available for other Anopheles species. Analyzed data on the status of resistance to different insecticides in anopheles vector species are provided.

The emergence of multiple insecticide resistance in An. culicifacies signifies the urgency for effective management strategies. Insecticide resistance management requires regular monitoring and implementation of innovative approaches for vector control, emphasizing the need for insecticides with a novel mode of action and integrated vector management methods. Gaps in the data and ways to address them and issues on insecticide resistance management are discussed.