Using artificial odors to optimize attractiveness of host decoy traps to malaria vectors.

Malaria vector surveillance tools often incorporate features of hosts that are attractive to blood-seeking females. The recently developed host decoy trap (HDT) combines visual, thermal, and olfactory stimuli associated with human hosts and has shown great efficacy in terms of collecting malaria vectors. Synthetic odors and yeast-produced carbon dioxide (CO2) could prove useful by mimicking the human odors currently used in HDTs and provide standardized and easy-to-use olfactory attractants. The objective of this study was to test the attractiveness of various olfactory attractant cues in HDTs to capture malaria vectors. We compared 4 different odor treatments in outdoor field settings in southern Benin and western Burkina Faso: the standard HDT using a human, HDT with yeast-produced CO2, HDT with an artificial odor blend, and HDT with yeast-produced CO2 plus artificial odor blend. In both experimental sites, the standard HDT that incorporated a real human produced the greatest catch of Anopheles gambiae s.l (Diptera: Culicidae). The alternatives tested were still effective at collecting target vector species, although the most effective included CO2, either alone (Benin) or in combination with synthetic odor (Burkina Faso). The trap using synthetic human odor alone caught the fewest An. gambiae s.l. compared to the other baited traps. Both Anopheles coluzzii and Anopheles gambiae were caught by each trap, with a predominance of An. coluzzii. Synthetic baits could, therefore, represent a more standardized and easier-to-deploy approach than using real human odor baits for a robust vector monitoring strategy.

Vectorial competence, insecticide resistance in Anopheles funestus and operational implications for malaria vector control strategies in Benin Republic.

The primary reason for the failure of malaria vector control across endemic regions is the widespread insecticide resistance observed in Anopheles vectors. The most dominant African vectors of malaria parasites are Anopheles gambiae and Anopheles funestus mosquitoes. These species often exhibit divergent behaviours and adaptive changes underscoring the importance of deploying active and effective measures in their control. Unlike An. gambiae, An. funestus mosquitoes are poorly studied in Benin Republic. However, recent reports indicated that An. funestus can adapt and colonize various ecological niches owing to its resistance against insecticides and adaptation to changing breeding habitats. Unfortunately, scientific investigations on the contribution of An. funestus to malaria transmission, their susceptibility to insecticide and resistance mechanism developed are currently insufficient for the design of better control strategies. In an attempt to gather valuable information on An. funestus, the present review examines the progress made on this malaria vector species in Benin Republic and highlights future research perspectives on insecticide resistance profiles and related mechanisms, as well as new potential control strategies against An. funestus. Literature analysis revealed that An. funestus is distributed all over the country, although present in low density compared to other dominant malaria vectors. Interestingly, An. funestus is being found in abundance during the dry seasons, suggesting an adaptation to desiccation. Among the An. funestus group, only An. funestus sensu stricto (s.s.) and Anopheles leesoni were found in the country with An. funestus s.s. being the most abundant species. Furthermore, An. funestus s.s. is the only one species in the group contributing to malaria transmission and have adapted biting times that allow them to bite at dawn. In addition, across the country, An. funestus were found resistant to pyrethroid insecticides used for bed nets impregnation and also resistant to bendiocarb which is currently being introduced in indoor residual spraying formulation in malaria endemic regions. All these findings highlight the challenges faced in controlling this malaria vector. Therefore, advancing the knowledge of vectorial competence of An. funestus, understanding the dynamics of insecticide resistance in this malaria vector, and exploring alternative vector control measures, are critical for sustainable malaria control efforts in Benin Republic.

Malaria-Transmitting Vectors Microbiota: Overview and Interactions With Anopheles Mosquito Biology.

Malaria remains a vector-borne infectious disease that is still a major public health concern worldwide, especially in tropical regions. Malaria is caused by a protozoan parasite of the genus Plasmodium and transmitted through the bite of infected female Anopheles mosquitoes. The control interventions targeting mosquito vectors have achieved significant success during the last two decades and rely mainly on the use of chemical insecticides through the insecticide-treated nets (ITNs) and indoor residual spraying (IRS). Unfortunately, resistance to conventional insecticides currently being used in public health is spreading in the natural mosquito populations, hampering the long-term success of the current vector control strategies. Thus, to achieve the goal of malaria elimination, it appears necessary to improve vector control approaches through the development of novel environment-friendly tools. Mosquito microbiota has by now given rise to the expansion of innovative control tools, such as the use of endosymbionts to target insect vectors, known as "symbiotic control." In this review, we will present the viral, fungal and bacterial diversity of Anopheles mosquitoes, including the bacteriophages. This review discusses the likely interactions between the vector microbiota and its fitness and resistance to insecticides.

P. falciparum msp1 and msp2 genetic diversity in P. falciparum single and mixed infection with P. malariae among the asymptomatic population in Southern Benin.

Plasmodium falciparum and Plasmodium malariae infections are prevalent in malaria-endemic countries. However, very little is known about their interactions especially the effect of P. malariae on P. falciparum genetic diversity. This study aimed to assess P. falciparum genetic diversity in P. falciparum and mixed infection P. falciparum/P. malariae isolates among the asymptomatic populations in Southern Benin. Two hundred and fifty blood samples (125 of P. falciparum and 125 P. falciparum/P. malariae isolates) were analysed by a nested PCR amplification of msp1 and msp2 genes. The R033 allelic family was the most represented for the msp1 gene in mono and mixed infection isolates (99.2% vs 86.4%), while the K1 family had the lowest frequency (38.3% vs 20.4%). However, with the msp2 gene, the two allelic families displayed similar frequencies in P. falciparum isolates while the 3D7 allelic family was more represented in P. falciparum/P. malariae isolates (88.7%). Polyclonal infections were also lower (62.9%) in P. falciparum/P. malariae isolates (p < 0.05). Overall, 96 individual alleles were identified (47 for msp1 and 49 for msp2) in P. falciparum isolates while a total of 50 individual alleles were identified (23 for msp1 and 27 for msp2) in P. falciparum/P. malariae isolates. The Multiplicity of Infection (MOI) was lower in P. falciparum/P. malariae isolates (p < 0.05). This study revealed a lower genetic diversity of P. falciparum in P. falciparum/P. malariae isolates using msp1 and msp2 genes among the asymptomatic population in Southern Benin.

Plasmodium falciparum msp1 and msp2 genetic diversity in parasites isolated from symptomatic and asymptomatic malaria subjects in the South of Benin.

Symptomatic and asymptomatic malaria patients are considered as the reservoirs of human Plasmodium. In the present study, we have evaluated the Plasmodium falciparum merozoite surface protein-1 (Pfmsp1) and protein-2 (Pfmsp2) genetic diversity among the symptomatic and asymptomatic malaria infection from health facilities in Cotonou, Benin Republic. A cross-sectional study recruited 158 individuals, including 77 from the asymptomatic and 81 from the symptomatic groups. The parasites were genotyped using Nested Polymerase Chain Reaction. Samples identified as Plasmodium falciparum were genotyped for their genetic diversity. No significant difference was observed in the overall multiplicity of infection (MOI) between the asymptomatic and symptomatic groups. In the symptomatic group, the overall frequency of K1, MAD20, and RO33 allelic family was more predominant (98.5%) followed by 3D7 (87.3%) and FC27 (83.1%). However, in asymptomatic group, the K1 alleles were the most prevalent (100%) followed by FC27 (89.9%), 3D7 (76.8%), MAD20 (60.5%), and RO33 (35.5%). The frequency of multiple allelic types (K1+MAD20+RO33) at the Pfmsp1 loci in the symptomatic infections was significantly higher when compared to that of the asymptomatic ones (97% vs. 34%, p < 0.05), whereas no difference was observed in the frequency of multiple allelic types (3D7 and FC27) at the Pfmsp2 loci between the two groups. The high presence of msp1 multiple infections in the symptomatic group compared to asymptomatic ones suggests an association between the genetic diversity and the onset of malaria symptoms. These data can provide valuable information in the development of a vaccine that could reduce the symptomatic disease.

Chemical composition and the insecticidal activity of Aeollanthus pubescens leaf essential oil against Anopheles gambiae sensu stricto.

BACKGROUND: The excessive use of synthetic insecticides is responsible for many cases of resistance in insects. Therefore, the use of natural molecules of ecological interest with insecticidal properties is an alternative approach to the use of synthetic insecticides. The aim of this study is to investigating the larvicidal and adulticidal activity and the chemical composition of the essential oil of Aeollanthus pubescens on the major malaria vector, Anopheles gambiae. METHODS: Three reference strains of Anopheles gambiae sensu stricto (Kisumu, Kiskdr and Acerkis) were used in this study. The leaves of A. pubescens were collected in southern Benin. The standard World Health Organisation (WHO) guidelines for larvicide evaluation were used, and the chemical composition of the essential oil was analysed by gas chromatography coupled to mass spectrometry. Adult mosquitoes of each strain were exposed to pieces of net coated with the essential oil for 3 min using the WHO cone bioassay method. Probit regression analysis was used to determine the concentrations that would kill 50 and 95% of each test population (LC50, LC95) and the knockdown time for 50 and 95% of each test population (KDT50, and KDT95). The difference between the mortality-dose regressions for the different strains was analysed using the likelihood ratio test (LRT). The log-rank test was performed to evaluate the difference in survival between the strains. RESULTS: A total of 14 components were identified, accounting for 98.3% of total oil content. The major components were carvacrol (51.1%), thymyle acetate (14.0%) and É£-terpinene (10.6%). The essential oil showed larvicidal properties on the Kisumu, Acerkis and Kiskdr strains, with LC50 of 29.6, 22.9 and 28.4 ppm, respectively. With pieces of netting treated at 165 µg/cm2, the KDT50 of both Acerkis (1.71 s; Z = 3.34, P < 0.001) and Kiskdr (2.67 s; Z = 3.49, P < 0.001) individuals were significantly lower than that of Kisumu (3.8 s). The lifespan of the three mosquito strains decreased to 1 day for Kisumu (χ2 = 99, df = 1, P < 0.001), 2 days for Acerkis (χ2 = 117, df = 1, P < 0.001) and 3 days for Kiskdr (χ2 = 96.9, df = 1, P < 0.001). CONCLUSION: Our findings show that A. pubescens essential oil has larvicide and adulticide properties against the malaria vector An. gambiae sensu stricto, suggesting that this essential oil may be a potential candidate for the control of the resistant malaria-transmitting vectors.