Roger Sanou

Most malaria vector control strategies target female Anopheles mosquitoes that transmit parasites, but emerging approaches such as gene drive, sterile insect technique, or Wolbachia require the release of males. Successful deployment depends on reliable knowledge of the species composition and age structure of male populations to overcome potential barriers to mating. Although approaches including near-infrared spectroscopy have been explored for male species identification and age grading, these methods remain constrained by limited validation, scalability, and accuracy under operational field conditions. Here we tested mid-infrared spectroscopy (MIRS) coupled with machine learning (ML) as a rapid and cost-effective approach for classifying species and age of male mosquitoes within the Anopheles gambiae complex. We used male mosquitoes from two laboratory-reared colonies in Burkina Faso (Anopheles coluzzii and An. gambiae) to develop a MIRS-ML model for species and age group (1–4, 5–10, 11–17 days) prediction under controlled conditions. This model was tested against a genetic and environmentally variable dataset consisting of male offspring obtained from gravid or blood fed Anopheles coluzzii and An. gambiae females collected from houses from two villages, Vallée du Kou and Soumousso and reared to adulthood in a semi-field system. The MIRS spectra from 2,120 males, representing both species, all age groups and both laboratory and semi-field backgrounds, were analysed using an extreme gradient boosting (XGBoost) algorithm to assess the ability to correctly predict age group and species. The XGBoost model classified mosquito species (86%) and age groups (85%) accurately in laboratory data, but performance declined under semi-field conditions (64% for species, 50% for age), reflecting environmental variability. Incorporating semi-field samples through transfer learning improved accuracy to 73% for species and 70% for age, underscoring both the limits of laboratory-only models and the value of transfer learning for enhancing generalisability in field settings. Our results demonstrate that mid-infrared spectroscopy with supervised machine learning (MIRS-ML) holds potential as a rapid tool for identifying the species and age group of cryptic male malaria vectors and represent one of the first applications of this approach to male Anopheles gambiae s.l. evaluated under semi-field conditions. However, before the approach can be used, larger datasets are needed to improve the classification algorithms and validate them for prediction in field populations.

Malaria transmission in sub-Saharan Africa is dominated by the An. gambiae complex and An. funestus group, whose distribution varies across ecological settings. Secondary species occur at lower densities, but their role in transmission may differ from one locality to another depending on local conditions. Assessing Anopheles biodiversity using ecological indices is therefore essential to characterise their diversity and relative abundance. This study investigated the biodiversity and spatial distribution of Anopheles species across the three climatic zones of Burkina Faso to guide effective vector control strategies. Indoor resting mosquitoes were collected from 67 health districts across the 13 regions of Burkina Faso between September and December 2022 using pyrethroid spray catches. A total of 30,521 Anopheles mosquitoes were identified, with An. gambiae s.l. dominating (94.4%). The Sudano-Sahelian zone recorded the highest abundance, followed by the Soudanian and Sahelian zones. Biodiversity decreased from humid southern to arid northern areas, with the Soudanian zone showing the highest diversity. Molecular analysis of 2026 An. gambiae s.l. specimens revealed marked heterogeneity: An. coluzzii predominated in Sahelian (74.9%) and Sudano-Sahelian (71.2%) zones, while An. gambiae s.s. was most frequent in the Soudanian zone (53.8%). These results highlight spatial and ecological differences in Anopheles composition across Burkina Faso and emphasize the need for locally adapted malaria vector control strategies.

Effective tools to prevent mosquito bites are essential for malaria control. The Lehmann Funnel Entry Trap (LFET), a window screen proven effective in reducing mosquito density, was tested for its large-scale impact on malaria vector control and community acceptance. A total of 1313 traps were deployed in Vallée du Kou 3 (VK3), with 12 traps randomly selected for detailed evaluation against untrapped houses in Vallée du Kou 5 (VK5). Traps were placed in windows with doors blocked by curtains. From July to October, mosquitoes were collected for nine days per month from VK3 traps and VK5 control houses. Morphological identification, density analysis, resistance gene screening, and female age structure determination were conducted. The trap’s impact was assessed via pyrethrum spray catch (PSC) and for nine days per month, while trap fabric integrity and community perceptions were also evaluated. Traps reduced mosquito entry density by more than 90% in VK3 houses. VK3 had 33% higher house mosquito density pre-intervention and 47% lower house mosquito density post-intervention than VK5. Old female mosquito numbers rose in VK5 but not VK3. Pyrethroid resistance was high (kdr mutation frequency > 0.9) in both control and intervention sites. VK3 residents appreciated the traps for reducing bites and improving sleep. The LFET effectively controls malaria vectors and is well-suited for widespread use in malaria elimination efforts.

Background There is a great need to find new effective tools to prevent mosquitoes from biting humans. As part of this search, the Lehmann Funnel Entry Trap, a window screen, was tested and has proven to be effective in mosquito density reduction in low and high vector density settings. Here we aimed to assess whether a large-scale deployment of pyriproxyfen-treated traps can control malaria mosquito populations and how well the traps were accepted at community level. Method Overall, 1,313 traps impregnated with Pyriproxyfen (PPF) were deployed. Of these, 12 traps in 12 houses were randomly selected across the intervention village, Vallée du Kou 3 (VK3), for indoor mosquito density assessment compared to houses without traps in the control village, Vallée du Kou 5 (VK5). Traps were placed in the windows, while doors were blocked with curtains. From July until October 2015, for nine days per month, mosquitoes were collected from the traps and matching houses in VK3, and in houses only in VK5. Anopheles coluzzii collected from the field as adults and as larvae reared through to adults and An. gambiae were used or released into traps to assess the bio-efficacy effect of PPF in VK3 against control mosquitoes from VK5. Then, mosquitoes that were in contact with the PPF trap netting were allowed to oviposit in the laboratory for fecundity and egg fertility reduction evaluation as compared to a control. The mosquitoes collected as part of the monthly programme were morphologically identified, counted, and preserved in 80% ethanol vials for subsequent analyses, including resistance genes and female mosquito age structure. The impact of the trap on mosquito density at community level was assessed by performing a pyrethrum spray catch (PSC). The integrity of net fabric as well as some sociological points of view on the trap’s efficacy and design were then reported. Results Overall mosquito density was reduced by ~ 90% in all houses equipped with traps in VK3. At the community level, while mosquito density before intervention was 33% higher in VK3 than in VK5, it was 47% higher in VK5 after the intervention. Old female mosquito numbers increased in VK5 by 12% in October but not in VK3, indicating that the traps were cumulatively killing older females. The additional effect of PPF was to limit egg-laying, with a smaller number of eggs counted, and with a lower hatching rate than in VK5. Mosquitoes were highly resistant to pyrethroids with a ~ 0.9 frequency of the kdr mutation. The trap was well accepted by the communities as most of the interviewees in VK3 found the traps reduced mosquito bites with peaceful sleep. They hoped to keep the traps in place beyond the study period. Conclusion The Lehmann Funnel Entry Trap has real potential to control malaria mosquito populations and can be widely used to sustain the global effort of malaria elimination.

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.

Every year, malaria kills approximately 405,000 people in Sub-Saharan Africa, most of them children under the age of five years. In many countries, progress in malaria control has been threatened by the rapid spread of resistance to antimalarial drugs and insecticides. Novel genetic mosquito control approaches could play an important role in future integrated malaria control strategies. In July 2019, the Target Malaria consortium proceeded with the first release of hemizygous genetically-modified (GM) sterile and non-transgenic sibling males of the malaria mosquito Anopheles coluzzii in Burkina Faso. This study aimed to determine the potential fitness cost associated to the transgene and gather important information related to the dynamic of transgene-carrying mosquitoes, crucial for next development steps. Bayesian estimations confirmed that GM males had lower survival and were less mobile than their wild type (WT) siblings. The estimated male population size in Bana village, at the time of the release was 28,000 - 37,000. These results provide unique information about the fitness and behaviour of released GM males that will inform future releases of more effective strains of the A. gambiae complex.

Background: The Lehmann Funnel Entry Trap has proven to be effective in catching and killing up to 70% of mosquitoes even in a high mosquito density setting. A medium-sized prototype was selected and deployed at large scale in Vallée du Kou 3 (VK3) in the Southwest of Burkina Faso to assess its entomological and sociological impact.Method: Overall, 1,313 traps impregnated with Pyriproxyfen (PPF), were deployed. Of them, 12 traps were randomly selected across the intervention village compared to houses without traps in the control village, Vallée du Kou 5 (VK5). Traps were placed at the windows while doors were blocked with curtains. Mosquitoes were collected in traps and matching houses in VK3 and in houses only in VK5, for nine days per month from July to October 2015. Collected mosquitoes were morphologically identified, counted, and preserved in 80% ethanol vials for subsequent analyses, including resistance genes and female mosquito age structure. The impact of the trap on mosquito density at community level was assessed by performing a pyrethrum spray catch (PSC) with bioassays to assess the effect of PPF. Results: Overall mosquito density was reduced by ~90% in all houses equipped with traps in VK3. At the community level, while mosquito density before intervention was 33% higher in VK3 than in VK5, it was 47% higher in VK5 after the intervention. Old female mosquito numbers increased in VK5 by 12% in October but not in VK3, indicating that the traps were cumulatively killing old females. The additional effect of PPF was to limit egg-laying, with a smaller number of eggs counted, and with a low hatching rate. Mosquitoes were highly resistant to pyrethroids with ~0.9 frequency of the kdr mutation. The trap was well accepted by the communities as 85.4% and 93.8% of interviewees in VK3 found the traps reducing mosquito bites with peaceful sleep respectively. Conclusion: The Lehmann Funnel Entry Trap has real potential to control malaria mosquito populations and can be widely used to sustain the global effort of malaria elimination.

Background: There is a global consensus that new intervention tools are needed for the final steps toward malaria elimination/eradication. In a recent study in Burkina Faso, the Lehmann Funnel Entry Trap (LFET) has shown promising results in the reduction of mosquito densities, even in areas where insecticide resistance is as high as 80%. The LFET requires no chemicals and is self-operated. However, one of the issues with the original LFET is the size of the funnel, which often occupies too much space within users’ homes. Here, the performance of three new, smaller-sized LFET prototypes that combine a screening and killing effect on mosquitoes was assessed. Methods: The study was carried out over three months during the rainy season in low and high malaria vector density sites, Soumousso and Vallée du Kou, respectively. The original LFET (or ‘Prototype 1’/‘P1’) was modified to produce three new prototypes, which were referred to as prototype 2 (‘the Medium’ or ‘P2’), prototype 3 (P3) and prototype 4 (P4). Each of the new prototypes was tested on eight days per month over the three-month period to assess their effectiveness in trapping and killing mosquitoes entering houses through the windows compared to the original LFET. Results: Overall, 78,435 mosquitoes (mainly Anopheles gambiae sensu lato) were collected in the two study sites, both in the traps and in the houses. A total of 56,430 (72%) mosquitoes were collected from the traps. In Vallée du Kou, the original LFET caught a greater number of mosquitoes than the medium (prototype 2), whereas no difference was observed between the other new prototypes (3 and 4) and the medium. In Soumousso, both the original and medium LFETs collected significantly greater numbers of mosquitoes compared to prototypes 3 and 4. Conclusion: This study has shown that the new LFET prototypes are effective in trapping mosquitoes in high mosquito density settings. A large-scale study with one of the prototypes will be needed to assess community acceptance of the traps and their ability to control malaria vectors.

Background There is a global consensus that new intervention tools are needed for the final steps toward malaria elimination/eradication. In a recent study in Burkina Faso, the Lehmann Funnel Entry Trap (LFET) has shown promising results in the reduction of mosquito densities, even in areas where insecticide resistance is as high as 80%. The LFET requires no chemicals and is self-operated. However, one of the issues with the original LFET is the size of the funnel, which often occupies too much space within users’ homes. Here, the performance of three new, smaller-sized LFET prototypes that combine a screening and killing effect on mosquitoes was assessed. Methods The study was carried out over three months during the rainy season in low and high malaria vector density sites, Soumousso and Vallée du Kou, respectively. The original LFET (or ‘Prototype 1’/’P1’) was modified to produce three new prototypes, which were referred to as Prototype 2 (‘the Medium’ or ‘P2’), Prototype 3 (P3) and Prototype 4 (P4). Each of the new prototypes was tested on eight days per month over the three-month period to assess their effectiveness in trapping and killing mosquitoes entering houses through the windows compared to the original LFET. Results Overall, 78,435 mosquitoes (mainly Anopheles gambiae sensu lato) were collected in the two study sites, both in the traps and in the houses. A total of 56,430 (72%) mosquitoes were collected from the traps. In Vallée du Kou, the original LFET caught a greater number of mosquitoes than the Medium (prototype 2), whereas no difference was observed between the other new prototypes (3 and 4) and the Medium. In Soumousso, both the original and Medium LFETs collected significantly greater numbers of mosquitoes compared to prototypes 3 and 4. Conclusion This study has shown that the new LFET prototypes are effective in trapping mosquitoes in high mosquito density settings. A large-scale study with one of the prototypes will be needed to assess community acceptance of the traps and their ability to control malaria vectors.

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 a mosquito. Monitoring the species-specific age structure of mosquito populations is critical to evaluating the impact of vector control interventions on malaria risk. We developed a rapid, cost-effective surveillance method based on deep learning of mid-infrared spectra of mosquitoes’ cuticle that simultaneously identifies the species and the age of three main malaria vectors, in natural populations. Using over 40,000 ecologically and genetically diverse females, we could speciate and age grade An. gambiae, An. arabiensis , and An. coluzzii with up to 95% accuracy. Further, our model learned the age of new populations with minimal sampling effort and detected the impact of control interventions on simulated mosquito populations, measured as a shift in their age structures. We anticipate our method to be applied to other arthropod vector-borne diseases.