Serosurvey of Chikungunya Virus in Old World Fruit Bats, Senegal, 2020-2022.

We conducted a cross-sectional serosurvey for chikungunya virus (CHIKV) exposure in fruit bats in Senegal during 2020-2023. We found that 13.3% (89/671) of bats had CHIKV IgG; highest prevalence was in Eidolon helvum (18.3%, 15/82) and Epomophorus gambianus (13.7%, 63/461) bats. Our results suggest these bats are naturally exposed to CHIKV.

Effects of insecticide resistance on the reproductive potential of two sub-strains of the malaria vector Anopheles coluzzii.

BACKGROUND & OBJECTIVES: The emergence and spread of insecticide resistance in African malaria vectors raise concerns over the control of malaria disease. Therefore, the implementation of better control strategies need a thorough understanding of the effects and mechanisms of resistance on vector adaptation capacities. We studied the effects of insecticide resistance on the reproductive potential of two laboratory sub-strains of the malaria vector Anopheles coluzzii characterised by phenotypic resistance/susceptibility to DDT. METHODS: The two sub-strains were selected from a laboratory strain of An. coluzzii using WHO test tubes. For each sub-strain, the number of produced and hatched eggs, developmental time, mosquito stages mortality, sex ratio and insemination rates after dissection of spermathecae were compared as measures of reproductive potential. RESULTS: Overall, the susceptible sub-strain produced higher but not significant mean numbers of eggs. However, the mean numbers of hatched eggs, larvae, pupae and adults were significantly lower than those of the resistant substrain. The mean time from egg-hatching to adult-emergence, egg-flooding to hatching, I instar to pupae and pupae to adult were similar between the two sub-strains. The mortality rates at the pupal stage were significantly different between the two sub-strains. Of the dissected spermathecae, 85.1% of the females from the resistant sub-strain were fertilized compared to 66.1% of the females from the susceptible sub-strain (p <0.0001). The resistant sub-strain produced more females in comparison to the susceptible sub-strain (respective mean sex ratio 1.37 vs 1.03, p = 0.01). INTERPRETATION & CONCLUSION: The results show differential life history traits between the two sub-strains of the malaria vector An. coluzzii, particularly fertility, insemination rate and sex ratio. They may have varied implications for insecticide resistance spread, monitoring and management; and hence underscore the need of further investigations before any generalization.

Dengue 1 outbreak in Rosso, northern Senegal, October 2021: entomologic investigations.

Senegal has experienced periodic epidemics of dengue in urban areas with increased incidence in recent years. However, few data are available on the local ecology of the epidemic vectors. In October 2021, a dengue outbreak was reported in northern Senegal to the Institute Pasteur de Dakar. Entomologic investigations then were undertaken to identify the areas at risk of transmission and to identify the vector(s). Adult mosquitoes were collected indoors and outdoors at selected households, while containers with water were inspected for mosquito larvae. All the Aedes aegypti (L.) collected were tested for dengue virus NS1 protein using a rapid diagnostic test (RDT), and positive samples were confirmed by real-time RT-PCR. The qRT-PCR positive samples were subjected to whole genome sequencing using Nanopore technology. The majority of the larvae-positive containers (83.1%) were used for water storage. The Breteau and Container indices exceeded the WHO-recommended thresholds for the risk of dengue virus transmission except at 2 localities. Ae. aegypti, the only reputed dengue vector, was collected resting indoors as well as outdoors and biting during the day and night. The NS1 protein was detected in 22 mosquito pools, including one pool of females emerging from field-collected larvae. All NS1-positive results were confirmed by RT-PCR. Virus serotyping showed that the outbreak was caused by DENV-1. This study demonstrates the need for continuous control of adult and aquatic stages of Ae. aegypti to prevent future dengue epidemics in Senegal. RDTs appear to be a promising tool for dengue diagnostics and surveillance.

Insecticide Resistance and Target-Site Mutations kdr, N1575Y, and Ace-1 in Anopheles gambiae s.l. Populations in a Low-Malaria-Transmission Zone in the Sudanian Region of Senegal.

Background/Objectives: Significant progress in malaria control has been achieved through long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), raising hopes for malaria elimination. However, emerging insecticide resistance threatens these gains. This study assessed the susceptibility of Anopheles gambiae s.l. populations to public health insecticides, examined the frequencies of kdr, Ace-1, and N1575Y mutations, and explored their associations with phenotypic resistance in Dielmo and Ndiop, Senegal. Methods: Anopheles larvae collected between September and December 2022 were reared to adulthood. Adult mosquitoes were exposed to discriminating concentrations of various insecticides following WHO guidelines. Knockdown times (KDT50 and KDT95) for pyrethroids were calculated using the Probit model. RT-qPCR detected target-site mutations (kdr: L1014F and L1014S, Ace-1, N1575Y) and assessed correlations with phenotypic resistance. Species-specific PCR identified species within the An. gambiae complex. Results/Conclusions: The populations of Dielmo and Ndiop showed susceptibility to pirimiphos-methyl and bendiocarb, with no Ace-1 mutation detected. Resistance to DDT and pyrethroids was observed. The knockdown times indicated that alphacypermethrin and lambdacyhalothrin were more effective than permethrin and deltamethrin. The L1014F allele was widespread, while L1014S was absent in Ndiop and low in Dielmo. The N1575Y mutation occurred only in populations with L1014F. The L1014S mutation was significantly associated with resistance to lambdacyhalothrin in both villages and to deltamethrin in Ndiop.