Variation in natural exposure to anopheles mosquitoes and its effects on malaria transmission.

Variation in biting frequency by Anopheles mosquitoes can explain some of the heterogeneity in malaria transmission in endemic areas. In this study in Burkina Faso, we assessed natural exposure to mosquitoes by matching the genotype of blood meals from 1066 mosquitoes with blood from residents of local households. We observed that the distribution of mosquito bites exceeded the Pareto rule (20/80) in two of the three surveys performed (20/85, 76, and 96) and, at its most pronounced, is estimated to have profound epidemiological consequences, inflating the basic reproduction number of malaria by 8-fold. The distribution of bites from sporozoite-positive mosquitoes followed a similar pattern, with a small number of individuals within households receiving multiple potentially infectious bites over the period of a few days. Together, our findings indicate that heterogeneity in mosquito exposure contributes considerably to heterogeneity in infection risk and suggest significant variation in malaria transmission potential

ACTIVITE BIOLOGIQUE ET MODES D’ACTION D’EXTRAITS DE QUATRE PLANTES AROMATIQUES CONTRE ANOPHELES GAMBIAE S.L. AU BURKINA FASO

Control of malaria vectors is based on insecticide-treated bednets and indoor residualsprays. These control methods are faced with the development of vectors resistance toward four classes of insecticides available. The research for new plant-based insecticides, including Ocimum canum Sims., Hyptis suaveolens Poit., Hyptis spicigera Lam. and Lantana camara L. responds to the need for an alternative to synthetic insecticides in the control of Anopheles gambiae s.l. complex, the major vector of malaria. The chemical compositions of essential oils (Eos) and extracts by various solventshave been identified and the standard protocols of the World Health Organization have been used for ovicidal, larvicidal and adulticidal tests. Evaluation of the oviposition deterrence effect was carried out using the Xue method. Eos extracted from these plants contain several compounds with a strong presence of monoterpenes. They demonstrated strong larvicidal, adulticidal, excito-repellent and oviposition deterrence activities against Anopheles gambiae. L. camara's Eos was more toxic to eggs (LC50 = 70.70 ppm), larvae (LC50 = 102.7 ppm for An. Coluzzii and LC50 = 92, 2 ppm for An. gambiae) and adults (LC50 = 0.84%). Inhibition of egg-laying was greater than 95% with all Eos tested from 500ppm. The solvent extracts showed great variability in their content of terpenoids, tannins, alkaloids, flavonoids, steroids and phenols. They were more toxic on larvae than adults of An. gambiae with higher toxicity of hexane extracts. Inhibition of egg production due to these extracts is greater than 74% from 500 ppm with L. camara and H. suaveolens. The concentrations of Eos inhibiting acetylcholinesterase ranged from 0.21 to 6.30 μg/ ml and were more active than the other extracts tested. The tests carried out on the resistant strain of An. gambiae s. l. with L. camara's Eos showed that this Eos can act on the voltagegate sodium channel to cause the mortality of resistant mosquitoes. The results of this study indicate that aromatic plant extracts can be used against An. gambiae with the need to adapt the type of extract to the mosquito stage. The Eos would act like carbamates but other modes of action seem to exist. Knowledge of the active substances and the implementation of appropriate formulations will make it possible to exploit this mosquito control alternative.La lutte contre les vecteurs du paludisme repose sur les moustiquaires imprégnées et les pulvérisations intradomiciliaires à base d’insecticides. Ces moyens de lutte sont confrontés au développement de la résistance des vecteurs vis-à-vis des quatre classes d’insecticides disponibles. La recherche de nouveaux insecticides à base de plantes, notamment Ocimum canum Sims., Hyptis suaveolens Poit., Hyptis spicigera Lam. et Lantana camara L. répond à la nécessité d’une alternative aux insecticides de synthèse dans la lutte contre le complexe Anopheles gambiae s.l., le vecteur majeur du paludisme. Les compositions chimiques des huiles essentielles (HE) et des extraits par divers solvants ont été identifiées et les protocoles standards de l’organisation mondiale de la santé ont été utilisés pour les tests ovicide, larvicide et adulticide. L’évaluation de l’effet d’inhibition de ponte a été réalisée grâce à la méthode de Xue. Les HE extraites de ces plantes renferment plusieurs composés avec une forte présence de monoterpènes. Elles ont manifesté de fortes activités larvicide, adulticide, excito-répulsive et d’inhibition de la ponte des femelles gravides de An. gambiae. L’HE de L. camara s’est illustrée avec une plus grande toxicité vis-à-vis des œufs (CL50 =70,70 ppm), des larves (CL50 =102,7 ppm pour An. coluzzii et CL50 = 92,2 ppm pour An. gambiae) et des adultes (CL50 = 0,84 %). L’inhibition de la ponte a été supérieure à 95 % avec toutes les HE testées à partir de 500ppm. Les extraits par les solvants ont présenté une grande variabilité dans leur teneur en terpénoïdes, tanins, alcaloïdes, flavonoïdes, stéroïdes et phénols. Ils ont été plus toxiques sur les larves que les adultes de An. gambiae avec une toxicité plus élevée des extraits hexaniques. L’inhibition de la ponte due à ces extraits est supérieure à 74% à partir de 500 ppm avec L. camara et H. suaveolens. Les concentrations des HE inhibitrices de l’acétylcholinestérase ont varié de 0,21 à 6,30 µg/ml et ont été plus actives que les autres extraits testés. Les tests réalisés sur la souche résistante de An. gambiae s. l. avec l’HE de L. camara ont montré que cette HE peut agir sur le canal sodium voltage-dépendant pour entrainer la mortalité des moustiques résistants. Les résultats de cette étude indiquent que les extraits de plantes aromatiques peuvent être utilisés contre An. gambiae avec la nécessité d’adapter le type d’extrait au stade du moustique. Les HE agiraient comme les carbamates mais d’autres modes d’action semblent exister. La connaissance des substances actives et la mise en place de formulations adaptées permettront une bonne exploitation de cette alternative de lutte contre les moustiques

ACTIVITE BIOLOGIQUE ET MODES D’ACTION D’EXTRAITS DE QUATRE PLANTES AROMATIQUES CONTRE ANOPHELES GAMBIAE S.L. AU BURKINA FASO

Control of malaria vectors is based on insecticide-treated bednets and indoor residualsprays. These control methods are faced with the development of vectors resistance towardfour classes of insecticides available. The research for new plant-based insecticides, includingOcimum canum Sims., Hyptis suaveolens Poit., Hyptis spicigera Lam. and Lantana camara L.responds to the need for an alternative to synthetic insecticides in the control of Anophelesgambiae s.l. complex, the major vector of malaria. The chemical compositions of essential oils (Eos) and extracts by various solventshave been identified and the standard protocols of the World Health Organization have beenused for ovicidal, larvicidal and adulticidal tests. Evaluation of the oviposition deterrenceeffect was carried out using the Xue method.Eos extracted from these plants contain several compounds with a strong presence ofmonoterpenes. They demonstrated strong larvicidal, adulticidal, excito-repellent andoviposition deterrence activities against Anopheles gambiae. L. camara's Eos was more toxicto eggs (LC50 = 70.70 ppm), larvae (LCThèse de Doctorat unique 50 = 102.7 ppm for An. Coluzzii and LC = 92, 2 ppmfor An. gambiae) and adults (LC = 0.84%). Inhibition of egg-laying was greater than 95%with all Eos tested from 500ppm.The solvent extracts showed great variability in their content of terpenoids, tannins, alkaloids,flavonoids, steroids and phenols. They were more toxic on larvae than adults of An. gambiaewith higher toxicity of hexane extracts. Inhibition of egg production due to these extracts isgreater than 74% from 500 ppm with L. camara and H. suaveolens. 50The concentrations of Eos inhibiting acetylcholinesterase ranged from 0.21 to 6.30 μg/ ml and were more active than the other extracts tested. The tests carried out on the resistantstrain of An. gambiae s. l. with L. camara's Eos showed that this Eos can act on the voltagegatesodium channel to cause the mortality of resistant mosquitoes. The results of this studyindicate that aromatic plant extracts can be used against An. gambiae with the need to adaptthe type of extract to the mosquito stage. The Eos would act like carbamates but other modesof action seem to exist. Knowledge of the active substances and the implementation ofappropriate formulations will make it possible to exploit this mosquito control alternative.La lutte contre les vecteurs du paludisme repose sur les moustiquaires imprégnées et lespulvérisations intradomiciliaires à base d’insecticides. Ces moyens de lutte sont confrontés audéveloppement de la résistance des vecteurs vis-à-vis des quatre classes d’insecticidesdisponibles. La recherche de nouveaux insecticides à base de plantes, notamment Ocimumcanum Sims., Hyptis suaveolens Poit., Hyptis spicigera Lam. et Lantana camara L. répond àla nécessité d’une alternative aux insecticides de synthèse dans la lutte contre le complexeAnopheles gambiae s.l., le vecteur majeur du paludisme.Les compositions chimiques des huiles essentielles (HE) et des extraits par divers solvants ontété identifiées et les protocoles standards de l’organisation mondiale de la santé ont étéutilisés pour les tests ovicide, larvicide et adulticide. L’évaluation de l’effet d’inhibition deponte a été réalisée grâce à la méthode de Xue.Les HE extraites de ces plantes renferment plusieurs composés avec une forte présence demonoterpènes. Elles ont manifesté de fortes activités larvicide, adulticide, excito-répulsive etd’inhibition de la ponte des femelles gravides de An. gambiae. L’HE de L. camara s’estillustrée avec une plus grande toxicité vis-à-vis des œufs (CLThèse de Doctorat unique 50 =70,70 ppm), des larves (CL=102,7 ppm pour An. coluzzii et CL50 = 92,2 ppm pour An. gambiae) et des adultes (CL =0,84 %). L’inhibition de la ponte a été supérieure à 95 % avec toutes les HE testées à partir de500ppm.Les extraits par les solvants ont présenté une grande variabilité dans leur teneur enterpénoïdes, tanins, alcaloïdes, flavonoïdes, stéroïdes et phénols. Ils ont été plus toxiques surles larves que les adultes de An. gambiae avec une toxicité plus élevée des extraitshexaniques. L’inhibition de la ponte due à ces extraits est supérieure à 74% à partir de 500ppm avec L. camara et H. suaveolens.Les concentrations des HE inhibitrices de l’acétylcholinestérase ont varié de 0,21 à 6,30µg/ml et ont été plus actives que les autres extraits testés. Les tests réalisés sur la soucherésistante de An. gambiae s. l. avec l’HE de L. camara ont montré que cette HE peut agir surle canal sodium voltage-dépendant pour entrainer la mortalité des moustiques résistants. Lesrésultats de cette étude indiquent que les extraits de plantes aromatiques peuvent être utiliséscontre An. gambiae avec la nécessité d’adapter le type d’extrait au stade du moustique. LesHE agiraient comme les carbamates mais d’autres modes d’action semblent exister. Laconnaissance des substances actives et la mise en place de formulations adaptées permettrontune bonne exploitation de cette alternative de lutte contre les moustiques

Distribution and insecticide resistance profile of the major malaria vector Anopheles funestus group across the African continent

There has been significant progress in malaria control in the last 2 decades, with a decline in mortality and morbidity. However, these gains are jeopardised by insecticide resistance, which negatively impacts the core interventions, such as insecticide-treated nets (ITN) and indoor residual spraying (IRS). While most malaria control and research efforts are still focused on Anopheles gambiae complex mosquitoes, Anopheles funestus remains an important vector in many countries and, in some cases, contributes to most of the local transmission. As countries move towards malaria elimination, it is important to ensure that all dominant vector species, including An. funestus, an important vector in some countries, are targeted. The objective of this review is to compile and discuss information related to A. funestus populations' resistance to insecticides and the mechanisms involved across Africa, emphasising the sibling species and their resistance profiles in relation to malaria elimination goals. Data on insecticide resistance in An. funestus malaria vectors in Africa were extracted from published studies. Online bibliographic databases, including Google Scholar and PubMed, were used to search for relevant studies. Articles published between 2000 and May 2023 reporting resistance of An. funestus to insecticides and associated mechanisms were included. Those reporting only bionomics were excluded. Spatial variation in species distribution and resistance to insecticides was recorded from 174 articles that met the selection criteria. It was found that An. funestus was increasingly resistant to the four classes of insecticides recommended by the World Health Organisation for malaria vector control; however, this varied by country. Insecticide resistance appears to reduce the effectiveness of vector control methods, particularly IRS and ITN. Biochemical resistance due to detoxification enzymes (P450s and glutathione-S-transferases [GSTs]) in An. funestus was widely recorded. However, An. funestus in Africa remains susceptible to other insecticide classes, such as organophosphates and neonicotinoids. This review highlights the increasing insecticide resistance of An. funestus mosquitoes, which are important malaria vectors in Africa, posing a significant challenge to malaria control efforts. While An. funestus has shown resistance to the recommended insecticide classes, notably pyrethroids and, in some cases, organochlorides and carbamates, it remains susceptible to other classes of insecticides such as organophosphates and neonicotinoids, providing potential alternative options for vector control strategies. The study underscores the need for targeted interventions that consider the population structure and geographical distribution of An. funestus, including its sibling species and their insecticide resistance profiles, to effectively achieve malaria elimination goals

Insecticide resistance levels and mechanisms in Aedes aegypti populations in and around Ouagadougou, Burkina Faso.

BACKGROUND:Recent outbreaks of dengue and other Aedes aegypti-borne arboviruses highlight the importance of a rapid response for effective vector control. Data on insecticide resistance and underlying mechanisms are essential for outbreak preparedness, but are sparse in much of Africa. We investigated the levels and heterogeneity of insecticide resistance and mechanisms of Ae. aegypti from contrasting settings within and around Ouagadougou, Burkina Faso. METHODOLOGY/PRINCIPAL FINDINGS:Bioassays were performed on larvae and adults to diagnose prevalence of resistance, and to assess levels where resistance was detected. Investigation of resistance mechanisms was performed using synergist bioassays, knockdown resistance (kdr) target site mutation genotyping and quantitative PCR expression analysis of candidate P450 genes. Larval dose-response assays indicated susceptibility to the organophosphates tested. Adult females were also susceptible to organophosphates, but resistance to carbamates was suspected in urban and semi-urban localities. Females from all localities showed resistance to pyrethroids but resistance prevalence and level were higher in urban and especially in semi-urban areas, compared to the rural population. Environment was also associated with susceptibility: adults reared from larvae collected in tires from the semi-urban site were significantly less resistant to pyrethroids than those collected from large outdoor drinking water containers ('drums'). Susceptibility to both pyrethroids tested was largely restored by pre-exposure to Piperonyl Butoxide (PBO), suggesting a strong metabolic basis to resistance. The 1534C kdr mutation was nearly fixed in semi-urban and urban areas but was far less common in the rural area, where the 1016I kdr mutation frequency was also significantly lower. P450 gene analysis detected limited over-expression of single candidates but significantly elevated average expression in the semi-urban site compared to both a susceptible laboratory colony, and females from the other collection sites. CONCLUSIONS/SIGNIFICANCE:Our results reveal pyrethroid resistance and paired kdr mutations in both urban and semi-urban sites at levels that are unprecedented for mainland Africa. The combination of target site and metabolic mechanisms is common in Ae. aegypti populations from other continents but is a worrying finding for African populations. However, organophosphate insecticides are still active against both larvae and adults of Ae. aegypti, providing useful insecticidal options for control and resistance management

Advances in the genetic characterization of the malaria vector, Anopheles funestus, and implications for improved surveillance and control

Abstract Anopheles mosquitoes present a major public health challenge in sub-Saharan Africa; notably, as vectors of malaria that kill over half a million people annually. In parts of the east and southern Africa region, one species in the Funestus group, Anopheles funestus, has established itself as an exceptionally dominant vector in some areas, it is responsible for more than 90% of all malaria transmission events. However, compared to other malaria vectors, the species is far less studied, partly due to difficulties in laboratory colonization and the unresolved aspects of its taxonomy and systematics. Control of An. funestus is also increasingly difficult because it has developed widespread resistance to public health insecticides. Fortunately, recent advances in molecular techniques are enabling greater insights into species identity, gene flow patterns, population structure, and the spread of resistance in mosquitoes. These advances and their potential applications are reviewed with a focus on four research themes relevant to the biology and control of An. funestus in Africa, namely: (i) the taxonomic characterization of different vector species within the Funestus group and their role in malaria transmission; (ii) insecticide resistance profile; (iii) population genetic diversity and gene flow, and (iv) applications of genetic technologies for surveillance and control. The research gaps and opportunities identified in this review will provide a basis for improving the surveillance and control of An. funestus and malaria transmission in Africa

First comprehensive analysis of Aedes aegypti bionomics during an arbovirus outbreak in west Africa: Dengue in Ouagadougou, Burkina Faso, 2016–2017

Background: Dengue’s emergence in West Africa was typified by the Burkina Faso outbreaks in 2016 and 2017, the nation’s largest to date. In both years, we undertook three-month surveys of Aedes populations in or near the capital city Ouagadougou, where the outbreaks were centered. Methodology: In 1200LG (urban), Tabtenga (peri-urban) and Goundry (rural) localities, we collected indoor and outdoor resting mosquito adults, characterized larval habitats and containers producing pupae and reared immature stages to adulthood in the laboratory for identification. All mosquito adults were identified morphologically. Host species (from which bloodmeals were taken) were identified by PCR. Generalized mixed models were used to investigate relationships between adult or larval densities and multiple explanatory variables. Results: From samples in 1,780 houses, adult Ae. aegypti were significantly more abundant in the two urban localities (Tabtenga and 1200 LG) in both years than in the rural site (Goundry), where Anopheles spp. were far more common. Results from adult collections indicated a highly exophilic and anthropophilic (>90% bloodmeals of human origin) vector population, but with a relatively high proportion of bloodfed females caught inside houses. Habitats producing most pupae were waste tires (37% of total pupae), animal troughs (44%) and large water barrels (30%). While Stegomyia indices were not reliable indicators of adult mosquito abundance, shared influences on adult and immature stage densities included rainfall and container water level, collection month and container type/purpose. Spatial analysis showed autocorrelation of densities, with a partial overlap in adult and immature stage hotspots. Conclusion: Results provide an evidence base for the selection of appropriate vector control methods to minimize the risk, frequency and magnitude of future outbreaks in Ouagadougou. An integrated strategy combining community-driven practices, waste disposal and insecticide-based interventions is proposed. The prospects for developing a regional approach to arbovirus control in West Africa or across Africa are discussed

Pyriproxyfen-treated bed nets reduce reproductive fitness and longevity of pyrethroid-resistant Anopheles gambiae under laboratory and field conditions

Background: The efficacy of insecticide-treated nets (ITNs) containing the insect growth regulator pyriproxyfen (PPF) and pyrethroid insecticides (PPF-ITNs) is being assessed in clinical trials to determine whether they provide greater protection from malaria than standard pyrethroid-treated ITNs in areas where mosquitoes are resistant to pyrethroids. Understanding the entomological mode of action of this new ITN class will aide interpretation of the results from these trials. Methods: Anopheles gambiae sensu lato (s.l.) mosquitoes from a susceptible laboratory strain were exposed to PPF-treated netting 24 h, 6 h, and immediately prior to, or 24 h post blood feeding, and the impact on fecundity, fertility and longevity recorded. Pyrethroid-resistant populations were exposed to nets containing permethrin and PPF (PPF-ITNs) in cone bioassays and daily mortality recorded. Mosquitoes were also collected from inside houses pre- and post-distribution of PPF-ITNs in a clinical trial conduced in Burkina Faso; female An. gambiae s.l. were then assessed for fecundity and fertility. Results: PPF exposure reduced the median adult lifespan of insecticide-susceptible mosquitoes by 4 to 5 days in all exposure times (p < 0.05) other than 6 h pre-blood meal and resulted in almost complete lifelong sterilization. The longevity of pyrethroid-resistant mosquitoes was also reduced by at least 5 days after exposure to PPF-ITNs compared to untreated nets, but was unaffected by exposure to standard pyrethroid only ITNs. A total of 386 blood-fed or gravid An. gambiae s.l. females were collected from five villages between 1 and 12 months before distribution of PPF-ITNs. Of these mosquitoes, 75% laid eggs and the remaining 25% appeared to have normal ovaries upon dissection. In contrast, only 8.6% of the 631 blood-fed or gravid An. gambiae s.l. collected post PPF-ITN distribution successfully oviposited; 276 (43.7%) did not oviposit but had apparently normal ovaries upon dissection, and 301 (47.7%) did not oviposit and had abnormal eggs upon dissection. Egg numbers were also significantly lower (average of 138/female prior distribution vs 85 post distribution, p < 0.05). Conclusion: Exposure to a mixture of PPF and pyrethroids on netting shortens the lifespan of mosquitoes and reduces reproductive output. Sterilization of vectors lasted at least one year under operational conditions. These findings suggest a longer effective lifespan of PPF-pyrethroid nets than reported previously