A new WHO bottle bioassay method to assess the susceptibility of mosquito vectors to public health insecticides: results from a WHO-coordinated multi-centre study.

BACKGROUND: The continued spread of insecticide resistance in mosquito vectors of malaria and arboviral diseases may lead to operational failure of insecticide-based interventions if resistance is not monitored and managed efficiently. This study aimed to develop and validate a new WHO glass bottle bioassay method as an alternative to the WHO standard insecticide tube test to monitor mosquito susceptibility to new public health insecticides with particular modes of action, physical properties or both. METHODS: A multi-centre study involving 21 laboratories worldwide generated data on the susceptibility of seven mosquito species (Aedes aegypti, Aedes albopictus, Anopheles gambiae sensu stricto [An. gambiae s.s.], Anopheles funestus, Anopheles stephensi, Anopheles minimus and Anopheles albimanus) to seven public health insecticides in five classes, including pyrethroids (metofluthrin, prallethrin and transfluthrin), neonicotinoids (clothianidin), pyrroles (chlorfenapyr), juvenile hormone mimics (pyriproxyfen) and butenolides (flupyradifurone), in glass bottle assays. The data were analysed using a Bayesian binomial model to determine the concentration-response curves for each insecticide-species combination and to assess the within-bioassay variability in the susceptibility endpoints, namely the concentration that kills 50% and 99% of the test population (LC50 and LC99, respectively) and the concentration that inhibits oviposition of the test population by 50% and 99% (OI50 and OI99), to measure mortality and the sterilizing effect, respectively. RESULTS: Overall, about 200,000 mosquitoes were tested with the new bottle bioassay, and LC50/LC99 or OI50/OI99 values were determined for all insecticides. Variation was seen between laboratories in estimates for some mosquito species-insecticide combinations, while other test results were consistent. The variation was generally greater with transfluthrin and flupyradifurone than with the other compounds tested, especially against Anopheles species. Overall, the mean within-bioassay variability in mortality and oviposition inhibition were < 10% for most mosquito species-insecticide combinations. CONCLUSION: Our findings, based on the largest susceptibility dataset ever produced on mosquitoes, showed that the new WHO bottle bioassay is adequate for evaluating mosquito susceptibility to new and promising public health insecticides currently deployed for vector control. The datasets presented in this study have been used recently by the WHO to establish 17 new insecticide discriminating concentrations (DCs) for either Aedes spp. or Anopheles spp. The bottle bioassay and DCs can now be widely used to monitor baseline insecticide susceptibility of wild populations of vectors of malaria and Aedes-borne diseases worldwide

Field evaluation of the biolarvicide, spinosad 20 per cent emulsifiable concentrate in comparison to its 12 per cent suspension concentrate formulation against Culex quinquefasciatus, the vector of bancroftian filariasis in India

Background & objectives: Biolarvicides may offer alternatives to chemical larvicides as these are known to be safe to environment and selective against the target species. However, only a limited number of biolarvicides have been approved for mosquito larval control. In the current study, a new formulation of spinosad, 20 per cent emulsifiable concentrate (EC) was tested for its efficacy against Culex quinquefasciatus, in comparison to its 12 per cent suspension concentrate (SC). Methods: Spinosad 20 per cent EC was tested against Cx. quinquefasciatus immature at 25, 50, 100 and 150 mg active ingredient (ai)/m[2] in cesspits, drains and abandoned wells in comparison with spinosad 12 per cent SC at the optimum field application dosage of 50 mg ai/m[2]. Results: The 20 per cent EC caused 90-100 per cent reduction of pupal density for 7-14 days in cesspits, 10-17 days in drains and 14-30 days in abandoned wells at all dosages tested. At lower dosages of 25 and 50 mg ai/m[2], >90 per cent reduction of pupal density was observed for one week in cesspits and street drains and for two weeks in abandoned wells. The effective duration of control provided by the higher dosages, 100 and 150 mg ai/m[2] was 1.4 to 2 times greater than the lower dosages, 25 and 50 mg ai/m[2]. Interpretation & conclusions: The findings showed that the spinosad 20 per cent EC can be used for larval control against Cx. quinquefasciatus, at the dosage of 25 mg ai/m[2] at weekly interval in cesspits and drains and at fortnightly interval in abandoned wells. Spinosad 20 per cent EC could be one of the options to be considered for larval control under integrated vector management

Bio-efficacy, physical integrity, community usage and washing practices of mosquito nets treated with ICON MAXX long-lasting insecticidal treatment in India

BACKGROUND New brands of potential long lasting insecticide nets (LLINs) and LLIN treatment kits require field evaluation before they are used in a vector control programme. OBJECTIVES The aim of this study was to evaluate the bio-efficacy, usage, washing practice and physical integrity of nets treated with LLIN treatment kit, ICON MAXX in a phase III field trial in Odisha state, India. METHODS A total of 300 polyester nets treated with ICON MAXX and 140 polyester nets treated conventionally with lambda-cyhalothrin CS 2.5% ITNs were distributed. The bio-efficacy was evaluated with WHO cone bioassay. The chemical analysis of netting pieces was done at the beginning, after 12 and 36 months of the trial. FINDINGS After one year of distribution of nets, the bioassay showed 100% mortality on both ITNs and ICON MAXX treated nets. At 36 months, the overall pass rate was 58.8% and the mean lambda-cyhalothrin content of LLINs was 34.5 mg ai/m2, showing a loss of 44.4% of the original concentration. CONCLUSION ICON MAXX treated LLIN was found to retain bio-efficacy causing 97% knockdown of Anopheles stephensi up to 30 months and met the WHOPES criteria. However, the desired bio-efficacy was not sustained up to 36 months

Evaluation of MAGNet, a long-lasting insecticidal mosquito net against Anopheles fluviatilis in experimental huts in India

Abstract Background MAGNet LN is a wash resistant long-lasting insecticidal (polyethylene) net (LLIN) in which the alpha-cypermethrin insecticide is incorporated within the 150 denier high density polyethylene monofilaments of the nets. The bio-efficacy of MAGNet LN was reported to be high even after 25 washes. The LN met the WHO criteria of Phase I evaluation and obtained recommendation from the World Health Organization Pesticide Evaluation Scheme (WHOPES) for Phase II trial. For registration of the LN in India, the current study was conducted to evaluate its efficacy after 20 or 25 washes compared to negative control (untreated net) and positive control (Duranet LN) in experimental huts against a wild, free flying pyrethroid susceptible population of Anopheles fluviatilis in terms of deterrence, blood-feeding inhibition, mortality and induced exophily. Methods The evaluation was carried out in six experimental huts located at Kandhaguda village in Malkangiri district, Odisha state following the WHO guidelines. Results The study showed that 25 times washed MAGNet LN produced 100% mortality in cone bioassays before and after hut evaluation. MAGNet washed 25 times did not differ significantly from all other treated nets in terms of deterring hut entry, induced exophily, blood feeding inhibition and causing mortality of An. fluviatilis. Conclusions MAGNet LN showed extended wash resistance retaining its bio-efficacy up to 25 washes and met the WHOPES requirement of passing Phase II evaluation

Synthesis and Characterization of ZnO Doped TiO2 Nanocomposites for Their Potential Photocatalytic and Antimicrobial Applications

As a result of the sol-gel method, we were able to produce pure ZnO and ZnO-doped TiO2 nanocomposites. The hexagonal wurtzite phase in ZnO products was discovered by powder X-ray diffraction (XRD). ZnO products are typically hexagonal wurtzite crystallites, formed according to the Debye Scherrer formula. Nanocomposites with significant morphological changes were created using the sol-gel process, including those that resembled rocks. To determine the composition of Zn, O, and Ti atoms in the samples, a multidimensional X-ray analysis was performed. There is an energy gap between 3.61 eV, as determined by UV-vis spectroscopy. In this study, pure ZnO and ZnO-doped TiO2 nanocomposites were used to study the degradation of methylene blue (MB) under visible light irradiation. Over an irradiation course of 6 h, a ZnO-doped TiO2 composite (84%) were studied. As determined by the kinetic analysis, nanocomposites made from pure ZnO and ZnO-doped TiO2 followed pseudo-first-order kinetics. In the presence of ZnO-doped TiO2 nanocomposites, antibacterial activity was significantly improved. This was shown to be effective against Gram-positive and Gram-negative bacteria (Escherichia coli and B. sublittus). There is evidence that the metal oxide nanocomposites that are produced can be used as an appropriate antimicrobial and disinfection alternative, particularly in biomedical settings, as reported in more detail

Synthesis and Characterization of ZnO Doped TiO₂ Nanocomposites for Their Potential Photocatalytic and Antimicrobial Applications

As a result of the sol-gel method, we were able to produce pure ZnO and ZnO-doped TiO2 nanocomposites. The hexagonal wurtzite phase in ZnO products was discovered by powder X-ray diffraction (XRD). ZnO products are typically hexagonal wurtzite crystallites, formed according to the Debye Scherrer formula. Nanocomposites with significant morphological changes were created using the sol-gel process, including those that resembled rocks. To determine the composition of Zn, O, and Ti atoms in the samples, a multidimensional X-ray analysis was performed. There is an energy gap between 3.61 eV, as determined by UV-vis spectroscopy. In this study, pure ZnO and ZnO-doped TiO2 nanocomposites were used to study the degradation of methylene blue (MB) under visible light irradiation. Over an irradiation course of 6 h, a ZnO-doped TiO2 composite (84%) were studied. As determined by the kinetic analysis, nanocomposites made from pure ZnO and ZnO-doped TiO2 followed pseudo-first-order kinetics. In the presence of ZnO-doped TiO2 nanocomposites, antibacterial activity was significantly improved. This was shown to be effective against Gram-positive and Gram-negative bacteria (Escherichia coli and B. sublittus). There is evidence that the metal oxide nanocomposites that are produced can be used as an appropriate antimicrobial and disinfection alternative, particularly in biomedical settings, as reported in more detail

Molecular modelling studies of <i>kdr</i> mutations in voltage gated sodium channel revealed significant conformational variations contributing to insecticide resistance

<p>Voltage gated sodium channels (VGSC) of mosquito vectors are the primary targets of dichlorodiphenyltrichloroethane (DDT) and other synthetic pyrethroids used in public health programmes. The knockdown resistant (<i>kdr</i>) mutations in VGSC are associated with the insecticide resistance especially in Anophelines. The present study is aimed to emphasize and demarcate the impact of three <i>kdr</i>-mutations such as L1014S, L1014F and L1014H on insecticide resistance. The membrane model of sodium transport domain of VGSC (STD-VGSC) was constructed using <i>de novo</i> approach based on domain and trans-membrane predictions. The comparative molecular modelling studies of wild type and mutant models of STD-VGSC revealed that L1014F mutant was observed to be near native to the wild type model in all the respects, but, L1014S and L1014H mutations showed drastic variations in the energy levels, root mean square fluctuations (RMSF) that resulted in conformational variations. The predicted binding sites also showed variable cavity volumes and RMSF in L1014S and L1014H mutants. Further, DDT also found be bound in near native manner to wild type in L1014F mutant and with variable orientation and affinities in L1014S and L1014H mutants. The variations and fluctuations observed in mutant structures explained that each mutation has its specific impact on the conformation of VGSC and its binding with DDT. The study provides new insights into the structure–function-correlations of mutant STD-VGSC structures and demonstrates the role and effects of <i>kdr</i> mutations on insecticide resistance in mosquito vectors.</p

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

<div><p> 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.</p></div