The southern districts of Odisha State in east-central India have been highly endemic for falciparum malaria for many decades. However, there is no adequate information on the abundance of the vector species or their bionomics in relation to space and time in these districts. Therefore, a study was carried out on the entomological aspects of malaria transmission to generate such information. Collections of mosquitoes were made once during each of the three seasons in 128 villages selected from eight districts. Villages within the foot-hill ecotype had a significantly greater abundance of Anopheles fluviatilis James s. l., whereas the abundance of Anopheles culicifacies Giles s. l. was significantly greater in the plain ecotype. The abundance of An. fluviatilis was maximum during the cold season, whereas An. culicifacies abundance was highest during summer and rainy seasons. The maximum likelihood estimation of the malaria infection rate in An. fluviatilis was 1.78%, 6.05%, and 2.6% in Ganjam, Kalahandi, and Rayagada districts, respectively. The infection rate of An. culicifacies was 1.39% only in Kandhamal district; infected females were not detected elsewhere. Concurrently, the annual malaria parasite incidence (MPI) was significantly higher in hill-top (17.6) and foot-hill (14.4) villages compared to plain villages (4.1). The districts with more villages in hill-top and foot-hill ecotypes also had a greater abundance of An. fluviatilis, the major malaria vector, and exhibited a higher incidence of malaria than villages within the plain ecotype, where An. culicifacies was the most abundant vector.

Background & objectives: In Odisha State, the control of malaria vectors has become dependent on synthetic pyrethroids, which are used for treatment of all approved long-lasting insecticidal nets (LLINs). The vast use of just one class of insecticide has led to the problem of resistance to insecticides in malaria vectors. One of the major malaria vectors in Odisha State is Anopheles culicifacies Giles. The aim of this study was to determine the resistance status of An. culicifacies to deltamethrin, a synthetic pyrethroid and other common insecticides used by the National Vector Borne Diseases Control Programme (NVBDCP) for indoor residual spraying in Odisha State. Methods: Mosquitoes were collected during April 2014 - June 2014 from 15 randomly selected villages in five Plasmodium falciparum endemic southern districts of Odisha State. The blood-fed wild caught females were exposed to the diagnostic dosage of DDT (4.0%), malathion (5.0%) and deltamethrin (0.05%) for one hour. Mortality was recorded at 24 h after the exposure. Results: Results indicated that An. culicifacies was resistant to all the three insecticides used in the malaria control programme in the five districts of Odisha State. Interpretation & conclusions: Resistance management strategy by appropriate rotation of different groups of insecticides including carbamates and incorporating a synergist with synthetic pyrethroids for treating mosquito nets should be considered for the control of malaria vectors in the area, especially where An. culicifacies is predominant. Periodical monitoring of susceptibility/resistance status of An. culicifacies to different insecticides is warranted.

Koraput, a predominantly tribe-inhabited and one of the highly endemic districts of Odisha State that contributes a substantial number of malaria cases to the India’s total. Control of malaria in such districts would contribute to change the national scenario on malaria situation. Hence, a study was carried out to measure the magnitude of malaria prevalence in the district to strengthen the malaria control activities.

Key words Japanese encephalitis; outbreak; entomological investigation; Malkangiri; Odisha; India

Background: Deltamethrin 62.5 polymer-enhanced suspension concentrate (SC-PE) is one of the World Health Organization-approved insecticides for indoor residual spraying and was recommended to evaluate its residual activity for determination of appropriate spray cycles in different eco-epidemiologic settings. In the current study, efficacy of deltamethrin 62.5 SC-PE was evaluated against vectors of malaria and its impact on malaria incidence in a Plasmodium falciparum hyper-endemic area in Koraput district, Odisha State, India. Methods: The trial had two comparable arms, arm 1 with residual spraying of deltamethrin 62.5 SC-PE and arm 2 with deltamethrin 2.5% WP (positive control). Comparative assessment of the impact of each intervention arm on entomological (density, parity, infection and human blood index), epidemiological (malaria incidence) parameters, residual efficacy and adverse effects were evaluated. Results: Both the arms were comparable in terms of entomological and epidemiological parameters. While, deltamethrin 62.5 SC-PE was found to be effective for 150 days in mud and wood surfaces and 157 days in cement surfaces; deltamethrin 2.5% was effective only for 105 days on mud surfaces and 113 days on cement and wood surfaces. Conclusions: Deltamethrin 62.5 SC-PE had prolonged killing effectiveness up to 5 months. Hence, one round of IRS with deltamethrin 62.5 SC-PE would be sufficient to cover two existing malaria peak transmission seasons (July–August and October–November) in many parts of India.

Development of resistance among the vectors to different insecticides poses a potential threat to vector control programme. Regular monitoring of susceptibility status of vector species to commonly used insecticides is recommended for planning appropriate vector control measures. In this communication, we have determined the phenotypic resistance of Anopheles culicifacies s.l., the major malaria vector against commonly used various insecticides in ten highly malaria endemic districts of Odisha State in east-central India. Bioassays were conducted before and after mass distribution of long-lasting insecticidal nets (LLINs) on field caught female mosquitoes with dichlorodiphenyl-trichloroethane (DDT), malathion and deltamethrin following the standard World Health Organization (WHO) guidelines. From the bioassays using 1x diagnostic concentrations (DC) recommended by WHO, we confirmed a higher frequency of resistant phenotype in An. culicifacies s.l. against DDT (range: 72% to 90%; average: 82%) compared to that against malathion(range: 17% to 34%; average: 26.7%) and deltamethrin (range: 14% to 24%; average: 19.1%) during 2018. Since, resistance to pyrethroid is detected; it is recommended to carry out bioassays of An. culicifacies s.l. exposing to higher concentrations of deltamethrin which would yield relevant information on the intensity of resistance and be useful to select suitable insecticide for resistance management vector control interventions.