Lina Ibrahim Abdallah

Anopheles arabiensis is a major malaria vector in Senegal, particularly in the Dakar region. The lack of a reference colony limits research on its biology and vector control. This study aimed to establish a stable An. arabiensis colony from urban populations in Keur Massar and Rufisque. Larvae were collected from 11 breeding sites and reared under controlled insectary conditions up to the F2 generation. Emergence rate, sex ratio, blood-feeding rate, and reproductive success were monitored. Species identification was performed morphologically and confirmed by PCR. Data were analyzed using R software, and differences between generations were assessed using Pearson’s chi-square test. Emergence rates in Keur Massar were 98.76%, 84.56%, and 85.15% for F0, F1, and F2, respectively, compared with 98.46%, 77.79%, and 86.22% in Rufisque. Females were most prevalent than the males, in both Keur Massar and Rufisque. In F2, blood-feeding rates reached 63.31% in Keur Massar and 90.91% in Rufisque. Eppendorf tubes inhibited oviposition, making group oviposition necessary for colony stabilization. PCR confirmed An. arabiensis. The study demonstrates the feasibility of establishing a stable An. arabiensis colony from Senegalese urban populations, providing a useful resource for future vector research and control strategies.

Malaria is a public health problem in Senegal, with heterogeneous transmission and little known about transmission drivers at the Senegalese border. This study aimed to determine bionomics of major vectors and malaria transmission in the Senegambian border. The study was conducted from July 2023 to March 2024 in Nemataba and Ndrame Ndimb (near the border), and in Medina Dianguette and Paoskoto (farther). Adult mosquitoes were collected using human landing catches and pyrethrum spray catches. Laboratory analyses were performed by Enzyme-Linked Immunosorbent Assay and Polymerase Chain Reaction techniques. Anopheles gambiae s.l. human biting rates (HBRs) were 1.05 bites/person/night (b/p/n) in Nemataba and 6.55 b/p/n in Ndrame Ndimb, while they were 14.73 b/p/n in Medina Dianguette and 1.47 b/p/n in Paoskoto. Anopheles funestus HBR was 2.88 b/p/n in Paoskoto and 0.37 b/p/n in Ndrame Ndimb. Human blood index for An. gambiae s.l. were 77.08% in Medina Dianguette, 66.67% in Nemataba, 2.42% in Ndrame Ndimb and 0 in Paoskoto, while for An. funestus they were 5.93% in Ndrame Ndimb and 3.65% in Paoskoto. Malaria transmission was detected in Medina Dianguette and Paoskoto, with 0.078 and 0.209 ib/p/n, respectively. This study highlights the diverse bionomic characteristics of major malaria vectors along the Senegambian border.

In Senegal, scaling up vector control has significantly reduced malaria, but coastal transmission remains a challenge due to secondary vectors like Anopheles melas. This exophilic and zoophilic species evades conventional indoor interventions, yet its bionomics and insecticide resistance profiles remain poorly characterized due to difficulties in laboratory colonization. Anopheles melas larvae were collected from brackish breeding sites in Mbine Coly (Mbour District). A laboratory colony was established from 26 PCR-confirmed founder females and stabilized up to the F17 generation by optimizing water salinity (10 g/L) and transitioning to communal oviposition. Standardized WHO tube bioassays were conducted on generations F2 to F9 to evaluate susceptibility to pyrethroids, organophosphates, and carbamates, alongside synergist tests using 4% piperonyl butoxide (PBO). The colony showed confirmed resistance to alpha-cypermethrin (81.7% mortality) and suspected resistance to deltamethrin (91.3%) and permethrin (94.3%). Pre-exposure to PBO fully restored susceptibility to deltamethrin and permethrin (100%), and significantly increased alpha-cypermethrin mortality to 96.3% (p < 0.001). While metabolic resistance typically involves multiple enzyme families including cytochrome P450s, glutathione S-transferases (GSTs), and esterases, these synergist results demonstrate a predominant role of cytochrome P450-mediated detoxification pathways in this population. Moderate-intensity resistance was confirmed for alpha-cypermethrin at 5× diagnostic doses. Conversely, the population was 100% susceptible to pirimiphos-methyl and bendiocarb. This study reports the successful long-term colonization of a wild An. melas strain for the first time and provides the first comprehensive evidence of multi-insecticide resistance in this population. The presence of high-intensity, metabolic pyrethroid resistance strongly justifies the immediate deployment of next-generation PBO-LLINs and the integration of organophosphates or carbamates in indoor residual spraying rotations to manage resistance in coastal Senegal.

In Senegal, scaling up vector control has significantly reduced malaria, but coastal transmission remains a challenge due to secondary vectors like Anopheles melas. This exophilic and zoophilic species evades conventional indoor interventions, yet its bionomics and insecticide resistance profiles remain poorly characterized due to difficulties in laboratory colonization. Anopheles melas larvae were collected from brackish breeding sites in Mbine Coly (Mbour District). A laboratory colony was established from 26 PCR-confirmed founder females and stabilized up to the F17 generation by optimizing water salinity (10 g/L) and transitioning to communal oviposition. Standardized WHO tube bioassays were conducted on generations F2 to F9 to evaluate susceptibility to pyrethroids, organophosphates, and carbamates, alongside synergist tests using 4% piperonyl butoxide (PBO). The colony showed confirmed resistance to alpha-cypermethrin (81.7% mortality) and suspected resistance to deltamethrin (91.3%) and permethrin (94.3%). Pre-exposure to PBO fully restored susceptibility to deltamethrin and permethrin (100%), and significantly increased alpha-cypermethrin mortality to 96.3% (p < 0.001), demonstrating a major cytochrome P450-mediated metabolic resistance. High-intensity resistance was confirmed for alpha-cypermethrin at 5X diagnostic doses. Conversely, the population was 100% susceptible to pirimiphos-methyl and bendiocarb. This study reports the successful long-term colonization of a wild An. melas strain for the first time and provides the first comprehensive evidence of multi-insecticide resistance in this population. The presence of high-intensity, metabolic pyrethroid resistance strongly justifies the immediate deployment of next-generation PBO-LLINs and the integration of organophosphates or carbamates in indoor residual spraying rotations to manage resistance in coastal Senegal.