Analysis of entomological indices for transmission of Japanese encephalitis in Malkangiri district, Odisha State, east central India during 2015-2019.

There have been repeated episodes of the outbreak of Japanese encephalitis (JE) in Malkangiri district of Odisha State in the recent past. In the current study, we aimed to assess the entomological parameters of JE vectors in the district. Prevalence of JE vector species, their per man hour density (PMHD), dusk index (DI), human blood index (HBI), infection status and other factors responsible for transmission of JE were assessed over 5 years (2015-2019). Culex vishnui was the predominant JE vector species (32.0%) collected, followed by Cx. whitmorei (27.1%) and Cx. tritaeniorhynchus (18.0%). The PMHD was higher in cattle shed (CS) than human dwelling (HD) and outdoor resting collection (ODRC) sites for all the JE vector species, except An. barbirostris. In particular, the PMHD of Cx. vishnui (8.02), Cx. whitmorei (5.71) and Cx. tritaeniorhynchus (5.01) were significantly higher in CS than HD and ODRC. The DI of Cx. vishnui (2.47), Cx. whitmorei (1.66) and Cx. tritaeniorhynchus (1.59) was significantly higher in CS compared to HD and ODRC. The HBI of Cx. vishnui was 0.015, whereas the HBI of Cx. tritaeniorhynchus was 0.009 in the study area. Among the 829 pools of JE vector species subjected to PCR, JE virus was isolated from one pool of Cx. vishnui. Based on the abundance of JE vectors and JE virus isolation from Cx. vishnui, it is requisite to implement systematic and long-term control measures for effective control of JE vector species in Malkangiri district, Odisha State.

Current status of malaria elimination in Koraput district of Odisha, India.

BACKGROUND & OBJECTIVES: After launching of NFME and NSP with wide scale implementation of effective intervention tools during 2017, Odisha State of India observed a drastic reduction of malaria cases (81%) in 2018 and 88.6% in 2019, compared to 2017. The current study analysed the different factors causative for malaria reduction in Koraput district of Odisha State, India. METHODS: The vector density and malaria incidences were assessed from January 2016 to December 2019 and human blood index, bio-efficacy and use rate of LLINs were assessed after distribution of long-lasting insecticidal nets. RESULTS: The use rate of LLINs by the villagers ranged from 93.8% to 100% throughout the year. The mortality of Anopheles jeyporiensis remained 100.0% in both DuraNet and PermaNet LNs. The density of An. fluviatilis after distribution of LLINs reduced from 4.7 to 0.0 whereas, the density of An. culicifacies reduced from 12.2 to 9.3. The HBI of An. fluviatilis and An. culicifacies was 0.006 and 0.005, respectively after distribution of LLINs. The malaria incidences also drop from 14.2 to zero after distribution. INTERPRETATION & CONCLUSION: A significant reduction in malaria incidences was validated and the possible reasons for the reduction are discussed.

Efficacy evaluation of Veeralin LN, a PBO-incorporated alpha-cypermethrin long-lasting insecticidal net against Anopheles culicifacies in experimental huts in Odisha State.

BACKGROUND: The success of malaria control using long-lasting insecticidal nets (LLINs) is threatened by pyrethroid resistance developed by the malaria vectors, worldwide. To combat the resistance, synergist piperonyl butoxide (PBO) incorporated LLINs is one of the available options. In the current phase II hut trial, the efficacy of Veeralin®LN (an alpha-cypermethrin and PBO-incorporated net) was evaluated against Anopheles culicifacies, a pyrethroid resistant malaria vector. METHODS: The performance of Veeralin®LN was compared with MAGNet®LN and untreated net in reducing the entry, induced exit, mortality and blood feeding inhibition of target vector species. RESULTS: The performance of Veeralin was equal to MAGNet in terms of reducing hut entry, inhibiting blood feeding and inducing exophily, and with regard to causing mortality Veeralin was better than MAGNet. When compared to untreated net, a significant reduction in hut entry and blood feeding and an increase in exophily and mortality were observed with Veeralin. In cone bioassays, unwashed Veeralin caused > 80% mortality of An. culicifacies. CONCLUSIONS: Veeralin performed equal to (entry, exit, feeding) or better than (mortality in huts and cone bioassays) MAGNet and could be an effective tool against pyrethroid resistant malaria vectors.

Intensity of pyrethroid resistance in Anopheles culicifacies s.l. (Diptera: Culicidae) in Odisha State, India.

ANOPHELES CULICIFACIES S.L: . is the principal malaria vector in India and has recently developed resistance to synthetic pyrethroids. For identifying the possible operational impact, quantitative measure of the intensity of this resistance is required. The purpose of this study was to measure the intensity of pyrethroid resistance in An. culicifacies s.l. The intensity bioassays with wild caught An. culicifacies s.l were carried out in 10 districts of east central India using 5x and 10x diagnostic concentrations of deltamethrin following WHO insecticides susceptibility guidelines. The results showed that the mortality of An. culicifacies s.l. ranged from 70% to 80% while exposed to 1x DC of deltamethrin (0.05%). Further bioassays conducted with 5x concentration of deltamethrin (0.25%) showed that the mortality of An. culicifacies s.l. in all the 10 districts varied from 92% to 97% indicating moderate resistance. While exposing to 10x concentration (0.5%) of this insecticide, 100% mortality was observed in all the districts; thereby confirmed moderate resistance intensity of this species. Since resistance was not confirmed at the 10x concentration, operational failure of this insecticide was unlikely. Hence, it is recommended to continue the use of LLINs for malaria vector control in these areas.

Evaluation of long-lasting indoor residual spraying of deltamethrin 62.5 SC-PE against malaria vectors in 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.

Entomological factors in relation to the occurrence of Japanese encephalitis in Malkangiri district, Odisha State, India.

Japanese encephalitis is a mosquito-borne arbo-viral disease with seasonal occurrence. Since 2009, AES/JE cases have been reported from Malkangiri district of Odisha State, India at an interval of one year.In the current study, the entomological parameters of known JE vector mosquito species were assessed for one year in Malkangiri district. Mosquito collections were done fortnightly in the index villages from August 2015 to July 2016 to record the density, their breeding habitats, feeding behaviour, parity, dusk index (DI) and infection status with JE virus. A total of 2347 JE vector mosquitoes belonging to nine species were collected from dusk collections. Culex vishnui (38.3%) was the predominant species followed by Cx. whitmorei (17.3%), Cx. fuscocephalus (13.6%), Cx. tritaeniorhynchus (11.1%), Cx. bitaeniorhynchus (6.1%), Anopheles subpictus (4.8%), An. barbirostris (4.4%), Cx. quinquefasciatus (2.3%) and Cx. gelidus (2.2%). The average DI of Cx. vishnui was 0.37 which was highest among all JE vector species and varied between 0.02 (April) and 0.9 (November). The human blood indexof Cx. vishnui was 0.026. A total of 1835 JE vector mosquitoes were screened for the isolation of JE virus, but none was found positive. Presence of paddy fields and ponds, abundance of JE vectors and their human feeding habit indicate the risk of JE transmission in the study area. Detection of JE virus in Cx. vishnui during 2016 outbreak in Malkangiri district further confirms that there would be a threat of JE transmission during the favourable period.

Multiple insecticide resistance in Anopheles culicifacies s.l. (Diptera: Culicidae) in east-central 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.

Entomological investigation of Japanese encephalitis outbreak in Malkangiri district of Odisha state, India.

BACKGROUND: A severe outbreak of Japanese encephalitis (JE) and acute encephalitis syndrome (AES) with high case fatality was reported from Malkangiri district of Odisha state, India during September to November 2016 affecting 336 children with 103 deaths. OBJECTIVES: The purpose of this study was to investigate the outbreak in the light of entomological determinants. METHODS: Entomological investigation was carried out in 48 villages from four mostly affected Community Health Centres (CHCs) of Malkangiri district. Dusk collections of resting adults was done in villages from indoor and outdoor sites to record the density of mosquito species, including the known JE vectors, feeding behaviour, parity, dusk index and infection status with JE virus (JEV). FINDINGS: The per man hour density and dusk index of JE vector species varied from 2.5 to 24.0 and 0.81 to 7.62, respectively in study villages. A total of 1136 mosquitoes belonging to six vector species were subjected to PCR and one pool of Culex vishnui was found to be positive for JEV. CONCLUSION: The JE transmission in Malkangiri district was confirmed. Thorough screening of human blood samples of JE/AES suspected cases and JE vector mosquitoes for the presence of JEV during rainy season every year is recommended.

Entomological investigation of Japanese encephalitis outbreak in Malkangiri district of Odisha state, India

BACKGROUND A severe outbreak of Japanese encephalitis (JE) and acute encephalitis syndrome (AES) with high case fatality was reported from Malkangiri district of Odisha state, India during September to November 2016 affecting 336 children with 103 deaths. OBJECTIVES The purpose of this study was to investigate the outbreak in the light of entomological determinants. METHODS Entomological investigation was carried out in 48 villages from four mostly affected Community Health Centres (CHCs) of Malkangiri district. Dusk collections of resting adults was done in villages from indoor and outdoor sites to record the density of mosquito species, including the known JE vectors, feeding behaviour, parity, dusk index and infection status with JE virus (JEV). FINDINGS The per man hour density and dusk index of JE vector species varied from 2.5 to 24.0 and 0.81 to 7.62, respectively in study villages. A total of 1136 mosquitoes belonging to six vector species were subjected to PCR and one pool of Culex vishnui was found to be positive for JEV. CONCLUSION The JE transmission in Malkangiri district was confirmed. Thorough screening of human blood samples of JE/AES suspected cases and JE vector mosquitoes for the presence of JEV during rainy season every year is recommended.

Preliminary study on susceptibility status of Anopheles minimus Theobald and An. fluviatilis James (Diptera: Culicidae) to DDT and deltamethrin in Keonjhar district of Odisha, India.

This study was carried out to determine the susceptibility levels of An. fluviatilis and An. minimus to DDT (4%) and deltamethrin (0.05%) and to select the insecticide to be used for routine national malaria vector control programme based on the results of the susceptibility test. Susceptibility test was done as per standard WHO susceptibility tests using DDT(4%) and deltamethrin (0.05%) in the villages of Keonjhar Districts during 2009. The results indicate that An. fluviatilis showed 100% mortality to DDT (4%) and deltamethrin (0.05%) and An. minimus showed 96.2 per cent mortality to DDT (4%) and 100 per cent to deltamethrin (0.05%). An. fluviatilis and An. minimus have been incriminated as the major malaria vectors of Keonjhar district. Successful application of DDT and deltamethrin could reduce the vector load from this area with consequent malaria control as these two species are found to be highly susceptible to DDT and deltamethrin. Another study as per WHO methodology is further recommended to substantiate the result of this study.