Entomological baseline data collection and power analyses in preparation of a mosquito swarm-killing intervention in south-western Burkina Faso

The mosquitocidal activity of isoxazoline derivatives afoxolaner, lotilaner, and fluralaner are not affected by mosquito sugar or antibiotic treatment

Long-lasting insecticidal nets and indoor residual sprays have played a major role in significantly reducing the burden of malaria. However, the management of mosquitoes resistant to current insecticides continues to be challenging. A promising new strategy is drug-based vector control where drugs are administered to vector hosts (human/animal), which renders the host blood toxic to mosquitoes-thereby reducing mosquito lifespan, fecundity and onward transmission of pathogens. Afoxolaner, fluralaner, and lotilaner are isoxazoline derivatives widely used as systemic insecticides for ectoparasite control in companion animals. Here, the mosquitocidal activity of these compounds against Anopheles gambiae s.s, Anopheles coluzzii, Aedes aegypti, and Anopheles funestus mosquitoes was evaluated. The effect of antibiotic treatment and different carbohydrates in artificial nectar meals on isoxazoline activity was also investigated. All isoxazolines tested showed rapid killing with little difference in susceptibility between different species and genera of mosquitoes. Fluralaner showed the most potent mosquitocidal effects with IC50 values ranging from 44 to 87 nM when mortality was assessed at 24 h post-feeding. Addition of the antibiotic cocktail or variations in sugar diet did not affect isoxazoline potency. In conclusion, data indicate potent and rapid mosquitocidal effects of isoxazolines that are likely unaffected by mosquito sugar feeding behaviour and microbiome dynamics.

Assessment of community-based resilience to malaria in two transmission settings in Western Burkina Faso

Malaria transmission in Burkina Faso is continuous throughout the year. Anthropogenic changes in the environment affect the risk of disease transmission and the ability of communities to respond. This study aimed to evaluate the resilience of two communities in different malaria transmission settings in Western Burkina Faso by examining their ability to absorb, adapt, and transform regarding malaria burden. Conducted in Western Burkina Faso, this study focused on two localities, Bana and VK5, representing two distinct malaria transmission settings: a natural savannah and a rice-growing environment. A mixed-methods approach was employed in this study. Quantitative data were collected through a census of compounds in the two localities: 75 compounds in VK5 and 104 in Bana, using the KoboToolbox platform. Qualitative data were gathered through semi-structured interviews with 13 individuals from both localities. Quantitative data were subjected to descriptive statistics, whereas qualitative data were processed manually. The results showed that both communities demonstrate resilience through preventive measures and socio-economic strategies. Universal bed net coverage was higher in VK5 (74.33%) than in Bana (61.39%), significantly reducing malaria cases (χ2 = 6.60, p = 0.0102). Communities adopted diverse economic adaptations, with 71.29% of compound chiefs in Bana and 78.38% in VK5 improving financial conditions through trade, farming, and vegetable cultivation. While Bana relied heavily on financial aid (76.47%) during illness, VK5 exhibited stronger community organization for environmental sanitation and broader social support networks. The strategies used to address malaria-related absences, the scope of solidarity networks available to assist affected families, and the nature of collective assistance provided, demonstrate that VK5 shows greater flexibility and resilience than Bana. Overall, the findings emphasize communities' commitment to improve their health and socioeconomic conditions. This commitment could be a key element in a potential community health insurance scheme.

Mosquitoes integrate visual and acoustic cues to mediate conspecific interactions in swarms

Male mosquitoes form aerial aggregations, known as swarms, to attract females and maximize their chances of finding a mate. Within these swarms, individuals must be able to recognize potential mates and navigate the social environment to successfully intercept a mating partner. Prior research has almost exclusively focused on the role of acoustic cues in mediating the male mosquito's ability to recognize and pursue females. However, the role of other sensory modalities in this behavior has not been explored. Moreover, how males avoid collisions with one another in the swarm while pursuing females remains poorly understood. In this study, we combined free-flight and tethered-flight simulator experiments to demonstrate that swarming Anopheles coluzzii mosquitoes integrate visual and acoustic information to track conspecifics and avoid collisions. Our tethered experiments revealed that acoustic stimuli gated mosquito steering responses to visual objects simulating nearby mosquitoes, especially in males that exhibited a strong response toward visual objects in the presence of female flight tones. Additionally, we observed that visual cues alone could trigger changes in mosquitoes' wingbeat amplitude and frequency. These findings were corroborated by our free-flight experiments, which revealed that Anopheles coluzzii modulate their thrust-based flight responses to nearby conspecifics in a similar manner to tethered animals, potentially allowing for collision avoidance within swarms. Together, these results demonstrate that both males and females integrate multiple sensory inputs to mediate swarming behavior, and for males, the change in flight kinematics in response to multimodal cues might allow them to simultaneously track females while avoiding collisions.

Multisensory integration in Anopheles mosquito swarms: The role of visual and acoustic information in mate tracking and collision avoidance

Male mosquitoes form aerial aggregations, known as swarms, to attract females and maximize their chances of finding a mate. Within these swarms, individuals must be able to recognize potential mates and navigate the dynamic social environment to successfully intercept a mating partner. Prior research has almost exclusively focused on the role of acoustic cues in mediating the male mosquito's ability to recognize and pursue flying females. However, the role of other sensory modalities in this behavior has not been explored. Moreover, how males avoid collisions with one another in the dense swarm while pursuing females remains poorly understood. In this study, we combined free-flight and tethered flight simulator experiments to demonstrate that swarming Anopheles coluzzii mosquitoes integrate visual and acoustic information to track conspecifics and avoid collisions. Our tethered experiments revealed that acoustic stimuli gated mosquito steering responses to visual objects simulating nearby mosquitoes, especially in males that exhibited attraction to visual objects in the presence of female flight tones. Additionally, we observed that visual cues alone could trigger changes in mosquitoes' wingbeat amplitude and frequency. These findings were corroborated by our free-flight experiments, which revealed that mosquitoes modulate their flight responses to nearby conspecifics in a similar manner to tethered animals, allowing for collision avoidance within swarms. Together, these results demonstrate that both males and females integrate multiple sensory inputs to mediate swarming behavior, and for males, the change in flight kinematics in response to multimodal cues allows them to simultaneously track females while avoiding collisions.

Spatial modelling of malaria prevalence associated with geographical factors in Houet province of Burkina Faso, West Africa

Malaria is a permanent threat to health in western Burkina Faso. Research has shown that geographical variables contribute to the spatial distribution in its transmission. The objective of this study is to assess the relationship between malaria prevalence and potential explanatory geographical variables in the Houet province in Burkina Faso. Statistics on malaria prevalence registered by health centres in the Houet province in 2017 and potential geographical variables identified through a literature review were collected. An Ordinary Least Squares (OLS) regression was used to identify key geographical variables and to measure their association with malaria while the Getis Ord Gi* index was used to locate malaria hotspots. The results showed that average annual temperature, vegetation density, percentage of clay in the soil, total annual rainfall and distance to the nearest waterbody are the main variables associated with malaria prevalence. These variables account for two-thirds of the spatial variability of malaria prevalence observed in Houet province. The intensity and direction of the relationship between malaria prevalence and geographical factors vary according to the variable. Hence, only vegetation density is positively correlated with malaria prevalence. Average temperature, for soil clay content, annual rainfall and for distance to the nearest water body are negatively correlated with the disease prevalence. These results show that even in an endemic area, malaria prevalence has significant spatial variation. The results could contribute to the choice of intervention sites, as this choice is crucial for reducing the malaria burden.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10708-022-10692-7.

Comparison of entomological impacts of two methods of intervention designed to control Anopheles gambiae s.l. via swarm killing in Western Burkina Faso

Outdoor biting constitutes a major limitation of current vector control based primarily on long-lasting insecticidal nets and indoor residual spraying, both of which are indoor interventions. Consequently, malaria elimination will not be achieved unless additional tools are found to deal with the residual malaria transmission and the associated vector dynamics. In this study we tested a new vector control approach for rapidly crashing mosquito populations and disrupting malaria transmission in Africa. This method targets the previously neglected swarming and outdoor nocturnal behaviors of both male and female Anopheles mosquitoes. It involved accurate identification and targeted spraying of mosquito swarms to suppress adult malaria vector populations and their vectorial capacities. The impact of targeted spraying was compared to broadcast spraying and evaluated simultaneously. The effects of the two interventions were very similar, no significant differences between targeted spraying and broadcast spraying were found for effects on density, insemination or parity rate. However, targeted spraying was found to be significantly more effective than broadcast spraying at reducing the number of bites per person. As expected, each intervention had a highly significant impact upon all parameters measured, but the targeted swarm spraying required less insecticide.