Phenotypic Insecticide Resistance in Anopheles gambiae (Diptera: Culicidae): Specific Characterization of Underlying Resistance Mechanisms Still Matters

An effective control of malaria vectors requires an extensive knowledge of mechanisms underlying the resistance-phenotypes developed by these vectors against insecticides. We investigated Anopheles gambiae mosquitoes from Benin and Togo for their intensity of insecticide resistance and we discussed the involvement of genotyped mechanisms in the resistance-phenotypes observed. Three- to five-day-old adult mosquitoes emerged from field and laboratory An. gambiae larvae were assayed using WHO tube intensity tests against various doses of deltamethrin: 1× (0.05%); 2× (0.1%); 5× (0.25%); 7.5× (0.375%) and those of pirimiphos-methyl: 0.5× (0.125%); 1× (0.25%). Members of An. gambiae complex were screened in field populations using polymerase chain reaction (PCR) assays. The presence of kdrR(1014F/1014S) and ace-1R(119S) mutations was also investigated using TaqMan and PCR-RFLP techniques, respectively. Anopheles gambiae from field were very resistant to deltamethrin, whereas KisKdr and AcerKdrKis strains displayed 100% mortality rates at 2× the diagnostic dose. In contrast, the field mosquitoes displayed a low resistance-intensity against 1× the diagnostic dose of pirimiphos-methyl, whereas AcerKis and AcerKdrKis strains showed susceptibility at 0.5× the diagnostic dose. Anopheles gambiae s.s., Anopheles coluzzii, and Anopheles arabiensis were identified. Allelic frequencies of kdrR (1014F) and ace-1R (119S) mutations in the field populations varied from 0.65 to 1 and 0 to 0.84, respectively. The field An. gambiae displayed high-resistance levels against deltamethrin and pirimiphos-methyl when compared with those of the laboratory An. gambiae-resistant strains. These results exhibit the complexity of underlying insecticide resistance mechanisms in these field malaria vectors

Genome-wide association studies reveal novel loci associated with pyrethroid and organophosphate resistance in Anopheles gambiae

Resistance to insecticides in Anopheles mosquitoes threatens the effectiveness of malaria control, but the genetics of resistance are only partially understood. We performed a large scale multi-country genome-wide association study of resistance to two widely used insecticides: deltamethrin and pirimiphos-methyl, using sequencing data from An. gambiae and An. coluzzii from ten locations in West Africa. Resistance was highly multi-genic, multiallelic and variable between populations. While the strongest and most consistent association with deltamethrin resistance came from Cyp6aa1, this was based on several independent copy number variants (CNVs) in An. coluzzii, and on a non-CNV haplotype in An. gambiae. For pirimiphos-methyl, signals included Ace1, cytochrome P450s, glutathione S-transferases and the nAChR target site of neonicotinoid insecticides. The regions around Cyp9k1 and the Tep family of immune genes showed evidence of cross-resistance to both insecticides. These locally-varying, multi-allelic patterns highlight the challenges involved in genomic monitoring of resistance, and form the basis for improved surveillance methods

Where is the ‘C’ in antenatal care and postnatal care: A multi‐country survey of availability of antenatal and postnatal care in low‐ and middle‐income settings

Objective: Antenatal (ANC) and postnatal care (PNC) are logical entry points for prevention and treatment of pregnancy‐related illness and to reduce perinatal mortality. We developed signal functions and assessed availability of the essential components of care. Design: Cross‐sectional survey. Setting: Afghanistan, Chad, Ghana, Tanzania, Togo. Sample: Three hundred and twenty‐one healthcare facilities. Methods: Fifteen essential components or signal functions of ANC and PNC were identified. Healthcare facility assessment for availability of each component, human resources, equipment, drugs and consumables required to provide each component. Main outcome measure: Availability of ANC PNC components. Results: Across all countries, healthcare providers are available (median number per facility: 8; interquartile range [IQR] 3–17) with a ratio of 3:1 for secondary versus primary care. Significantly more women attend for ANC than PNC (1668 versus 300 per facility/year). None of the healthcare facilities was able to provide all 15 essential components of ANC and PNC. The majority (>75%) could provide five components: diagnosis and management of syphilis, vaccination to prevent tetanus, BMI assessment, gestational diabetes screening, monitoring newborn growth. In Sub‐Saharan countries, interventions for malaria and HIV (including prevention of mother to child transmission [PMTCT]) were available in 11.7–86.5% of facilities. Prevention and management of TB; assessment of pre‐ or post‐term birth, fetal wellbeing, detection of multiple pregnancy, abnormal lie and presentation; screening and support for mental health and domestic abuse were provided in <25% of facilities. Conclusions: Essential components of ANC and PNC are not in place. Focused attention on content is required if perinatal mortality and maternal morbidity during and after pregnancy are to be reduced

Towards an intelligent malaria outbreak warning model based intelligent malaria outbreak warning in the northern part of Benin, West Africa

Abstract Background Malaria is one of the major vector-borne diseases most sensitive to climatic change in West Africa. The prevention and reduction of malaria are very difficult in Benin due to poverty, economic insatiability and the non control of environmental determinants. This study aims to develop an intelligent outbreak malaria early warning model driven by monthly time series climatic variables in the northern part of Benin. Methods Climate data from nine rain gauge stations and malaria incidence data from 2009 to 2021 were extracted from the National Meteorological Agency (METEO) and the Ministry of Health of Benin, respectively. Projected relative humidity and temperature were obtained from the coordinated regional downscaling experiment (CORDEX) simulations of the Rossby Centre Regional Atmospheric regional climate model (RCA4). A structural equation model was employed to determine the effects of climatic variables on malaria incidence. We developed an intelligent malaria early warning model to predict the prevalence of malaria using machine learning by applying three machine learning algorithms, including linear regression (LiR), support vector machine (SVM), and negative binomial regression (NBiR). Results Two ecological factors such as factor 1 (related to average mean relative humidity, average maximum relative humidity, and average maximal temperature) and factor 2 (related to average minimal temperature) affect the incidence of malaria. Support vector machine regression is the best-performing algorithm, predicting 82% of malaria incidence in the northern part of Benin. The projection reveals an increase in malaria incidence under RCP4.5 and RCP8.5 over the studied period. Conclusion These results reveal that the northern part of Benin is at high risk of malaria, and specific malaria control programs are urged to reduce the risk of malaria

Improving the efficiency of Beauveria bassiana applications for sustainable management of Plutella xylostella (Lepidoptera: Plutellidae) in West Africa

The effectiveness of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin isolates Bb11, Bb115, Bb116 and Bb362 against the diamondback moth (DBM), Plutella xylostella (L.) population from Cotonou, Benin, was investigated in the laboratory and on station. In the laboratory, six concentrations, 104, 105, 106, 107, 108 and 109 conidia/ml of each isolate were used to assess B. bassiana virulence. Third instar DBM larvae were inoculated with 2 µl of each isolate's concentrations by topical application method. Control larvae were inoculated with sterilized Tween 80 solution (0.05%). Compared with other isolates, Bb11 was more virulent against DBM with LD50 value estimated to 4.96 × 106 conidia/ml and the highest rates of cadaver sporulation. The effectiveness of Bb11 against DBM on cabbage was subsequently assessed on station and on farm in Benin and Togo, at a low doses of 53 g/ha once or twice a week and a high dose of 315 g/ha weekly. Compared with unsprayed control and deltamethrin treatments, the dose of 53 g/ha of Bb11 applied twice a week at intervals of 4 days was able to reduce on farm the density of DBM by 83% and 93%, respectively. Also, the marketable cabbage yield obtained on farm with this dose was significantly higher compared with the other treatments, with a 199% and 452% increase in Danyi and Cotonou over the unsprayed control, respectively. These results confirm the better performance of Bb11 over other isolates, and also indicate that the newly investigated application dosage and frequency of Bb11 could be an efficient management option to control DBM in Benin and Togo

Molecular xenomonitoring for post-validation surveillance of lymphatic filariasis in Togo: no evidence for active transmission.

BACKGROUND Lymphatic filariasis (LF) is a mosquito-borne filarial disease targeted for elimination by the year 2020. The Republic of Togo undertook mass treatment of entire endemic communities from 2000 to 2009 to eliminate the transmission of the disease and is currently the first sub-Saharan African country to be validated by WHO for the elimination of LF as a public health problem. However, post-validation surveillance activities are required to ensure the gains achieved are sustained. This survey assessed the mosquito vectors of the disease and determined the presence of infection in these vectors, testing the hypothesis that transmission has already been interrupted in Togo. METHOD Mosquitoes were collected from 37 villages located in three districts in one of four evaluation units in the country. In each district, 30 villages were selected based on probability proportionate to size; eight villages (including one of the 30 villages already selected) where microfilaremia-positive cases had been identified during post-treatment surveillance activities were intentionally sampled. Mosquitoes were collected using pyrethrum spray collections (PSC) in households randomly selected in all villages for five months. In the purposefully selected communities, mosquitoes were also collected using human landing collections (HLC) and exit traps (ET). Collected mosquitoes were identified morphologically, and the identification of Wuchereria bancrofti DNA in the mosquitoes was based on the pool screening method, using the LAMP assay. RESULTS A total of 15,539 mosquitoes were collected during the study. Anopheles gambiae (72.6%) was the predominant LF vector collected using PSC. Pool screen analysis of 9191 An. gambiae in 629 pools revealed no mosquitoes infected with W. bancrofti (0%; CI: 0-0.021). CONCLUSIONS These results confirm the findings of epidemiological transmission assessment surveys conducted in 2012 and 2015, which demonstrated the absence of LF transmission in Togo. The challenges of implementing molecular xenomonitoring are further discussed

Efficacy of two PBO long lasting insecticidal nets against natural populations of Anopheles gambiae s.l. in experimental huts, Kolokopé, Togo.

LLINs containing an insecticide plus the synergist, piperonyl butoxide (PBO) have been designed for increased efficacy against pyrethroid-resistant malaria vectors. In this study, two LLINs with PBO, PermaNet® 3.0 and Olyset® Plus, and a pyrethroid-only LLIN, Yorkool®, were evaluated in experimental huts against a free-flying, wild population of Anopheles gambiae s.l. in Kolokopé, a cotton cultivated area of Togo. WHO susceptibility tube tests and subsequent molecular assays determine the An. gambiae s.l. populations to be resistant to pyrethroids and DDT with both target site kdr and metabolic resistance mechanisms involved in the resistance observed. Anopheles gambiae s.s. and An. coluzzi were present in sympatry though the kdr (L1014F) mutation was observed at a higher frequency in An. gambiae s.s. The experimental hut results showed that both PermaNet® 3.0 and Olyset® Plus nets induced similar levels of deterrence, exophily, and reduced blood feeding rate against wild An. gambiae s.l. in contrast to the pyrethroid only LLIN, Yorkool®. The proportion of wild An. gambiae s.l. killed by unwashed PermaNet® 3.0 was significantly higher than unwashed Olyset® Plus (corrected mortality 80.5% compared to 66.6%). Similar blood feeding inhibition rates were observed for unwashed PermaNet® 3.0 and Olyset® Plus; however, PermaNet® 3.0 washed 20 times demonstrated significantly higher blood feeding inhibition rate than Olyset® Plus washed 20 times (91.1% compared with 85.6% respectively). Yorkool® performed the worst for all the parameters evaluated. In an area of pyrethroid resistance of An. gambiae s.l involving kdr target site and metabolic resistance mechanisms, LLINs with PBO can provide additional protection in terms of reduction in blood feeding and increase in mosquito mortality compared to a pyrethroid-only net, and should be considered in malaria vector control strategies