Targeted application of an organophosphate-based paint applied on windows and doors against Anopheles coluzzii resistant to pyrethroids under real life conditions in Vallée du Kou, Burkina Faso (West Africa)

Essential Oils From Five Local Plants: An Alternative Larvicide for Anopheles gambiae s.l. (Diptera: Culicidae) and Aedes aegypti (Diptera: Culicidae) Control in Western Burkina Faso

Introduction

Malaria and dengue are two main vector-borne infectious diseases transmitted by Anopheles gambiae and Aedes aegypti, respectively, in tropical and subtropical regions. The concern for environmental safety and the increasing development of resistance to the chemical in main arthropod vectors raises interest in the search for botanicals such as essential oils (EOs) that can be used in vector control.

Methods

Larvicidal bioassays were performed according to the WHO standard methods using Ae. aegypti and An. gambiae larvae collected from Bobo-Dioulasso and in the Kou Valley (VK), respectively, two areas located in Houet Province of western Burkina Faso. Kisumu and Bora bora, the susceptible strains of An. gambiae and Ae. aegypti, respectively, were used as controls. OEs extracted from leaves of five aromatic plants, Cymbopogon citratus, Cymbopogon nardus, Eucalyptus camaldulensis, Lippia multiflora, and Ocimum americanum, naturally growing in Burkina Faso were tested. The pyriproxyfen was used as a positive control.

Results

As a result, the lethal concentrations (LC50) for Ae. aegypti from Bobo-Dioulasso and An. gambiae from VK ranged from 41.9 to 103.8 ppm and 39.5 to 138.1 ppm, respectively. As for LC90 values, they ranged from 74.6 to 311.3 ppm for Ae. aegypti from Bobo-Dioulasso and from 90.2 to 328.9 ppm for An. gambiae from VK. Among the EOs tested, L. multiflora showed the highest activity against all the strains of An. gambiae and Ae. aegypti larvae. No difference in terms of LC50 values was found between L. multiflora and pyriproxyfen used as a positive control on An. gambiae larvae. It is not the case for Aedes aegypti populations, where pyriproxyfen remains the most toxic. Overall, An. gambiae populations were the most susceptible to EOs tested as compared to Ae. aegypti populations.

Conclusion

Our study furthers our knowledge of the larvicidal activity of EOs in the western part of Burkina and opens new avenues in their putative use in vector control strategies.

Organophosphate Insecticide Exposure Impacts Reproductive Success in Insensitive Acetylcholinesterase Anopheles gambiae Mosquitoes

Extensive use of insecticides has led to the selection of resistance alleles in malaria vectors threatening the control programs. Even if mosquitoes are not killed directly in the contact of insecticide-treated bed nets, their capacity to transmit malaria parasite could be decreased because of the consequences on their life-history traits after repeated exposure. The current work investigated the effects of organochlorine, carbamate, organophosphate, and pyrethroid insecticide exposure on the reproductive success in Anopheles gambiae s.s. Two Anopheles gambiae strains, AcerKis, KisKdr, were used. According to WHO recommendations, female mosquitoes of these resistant strains were exposed to discriminant doses of DDT, chlorpyriphos-methyl, bendiocarb, and permethrin insecticides. Surviving mosquitoes were then fed and allowed to lay eggs. Fecundity was assessed by examining the number of eggs per mosquito, the number of larvae per egg batch and larval hatching rates were used to evaluate the fertility. The data showed that AcerKis females surviving chlorpyriphos-methyl exposure significantly laid few eggs. No significant difference in the hatching rate was noticed in AcerKis females exposed to bendiocarb compared to their control. No significant effect on the fecundity and fertility was observed in KisKdr females exposed to permethrin. Our finding showed that organophosphate insecticides represented here by chlorpyriphos-methyl could hamper egg-laying in insensitive acetylcholinesterase An. gambiae female mosquitoes. This knowledge could help design alternative vector control strategies targeting fecundity and fertility in resistant malaria vectors.

Rapid age-grading and species identification of natural mosquitoes for malaria surveillance

The malaria parasite, which is transmitted by several Anopheles mosquito species, requires more time to reach its human-transmissible stage than the average lifespan of mosquito vectors. Monitoring the species-specific age structure of mosquito populations is critical to evaluating the impact of vector control interventions on malaria risk. We present a rapid, cost-effective surveillance method based on deep learning of mid-infrared spectra of mosquito cuticle that simultaneously identifies the species and age class of three main malaria vectors in natural populations. Using spectra from over 40, 000 ecologically and genetically diverse An. gambiae, An. arabiensis, and An. coluzzii females, we develop a deep transfer learning model that learns and predicts the age of new wild populations in Tanzania and Burkina Faso with minimal sampling effort. Additionally, the model is able to detect the impact of simulated control interventions on mosquito populations, measured as a shift in their age structures. In the future, we anticipate our method can be applied to other arthropod vector-borne diseases.

Knowing the age of malaria-transmitting mosquitoes is important to understand transmission risk as only old mosquitoes can transmit the disease. Here, the authors develop a method based on mid-infrared spectra of mosquito cuticle that can rapidly identify the species and age class of main malaria vectors.

Insecticide resistance mechanisms in Anopheles gambiae complex populations from Burkina Faso, West Africa

Vector control constitutes a fundamental approach in reducing vector density and the efficient option to break malaria transmission in Africa. Malaria vectors developed resistance to almost all classes of insecticides recommended by WHO for vector control in most places of African countries and may compromise the vector control strategies. This study updated the resistance status of Anopheles gambiae complex populations to insecticides recommended for vector control in the western part of Burkina Faso. Insecticide susceptibility bioassays were performed on seven natural populations of An. gambiae complex from western Burkina Faso in the 2016 rainy season using the WHO protocol. Biochemical assays were carried out according to the WHO protocol on the same populations to estimate detoxifying enzymes activities including non-specific esterases (NSEs), oxidases (cytochrome P450) and Glutathione-S-Transferases (GSTs). Polymerase Chain Reactions (PCRs) were performed for the identification of the An. gambiae complex species as well as the detection of kdr-west and ace-1 mutations. Susceptibility bioassays showed that An. gambiae complex was multi-resistant to pyrethroids, DDT and carbamates in almost all areas. The mortality rates ranged from 10 to 38%, 2.67 to 59.57% and 64.38 to 98.02% for Deltamethrin, DDT and Bendiocarb respectively. A full susceptibility (100%) to an organophosphate, the Chlorpyrifos-methyl, was observed at the different sites. Three (3) species of the An. gambiae complex were identified: An. gambiae s.s, An. coluzzii and An. arabiensis. The frequencies of the kdr-w mutation were highly widespread (0.66 to 0.98) among the three species of the complex. The ace-1 mutation was detected at low frequencies (0 to 0.12) in An. gambiae s.s and An. coluzzii. A high level of GSTs and NSEs were observed within the different populations of the An. gambiae complex. Several mechanisms of insecticide resistance were found simultaneously in the same populations of An. gambiae complex conferring high multi-resistance to DDT, Carbamate and Pyrethroids. The full susceptibility of An. gambiae complex to organophosphates is a useful data for the national malaria control program in selecting the most appropriate products to both maintain the effectiveness of vector control strategies and best manage insecticide resistance as well as developing new alternative strategies for the control of major malaria vectors in Burkina Faso.