Background: Malaria vector control in Africa depends upon effective insecticides in bed nets and indoor residual sprays. This study investigated the extent of insecticide resistance in Anopheles gambiae s.l., Anopheles gambiae s.s. and Anopheles arabiensis in western Kenya where ownership of insecticide-treated bed nets has risen steadily from the late 1990s to 2010. Temporal and spatial variation in the frequency of a knock down resistance (kdr) allele in A. gambiae s.s. was quantified, as was variation in phenotypic resistance among geographic populations of A. gambiae s.l.
Methods: To investigate temporal variation in kdr frequency, individual specimens of A. gambiae s.s. from two sentinel sites were genotyped using RT-PCR from 1996-2010. Spatial variation in kdr frequency, species composition, and resistance status were investigated in additional populations of A. gambiae s.l. sampled in western Kenya in 2009 and 2010. Specimens were genotyped for kdr as above and identified to species via conventional PCR. Field-collected larvae were reared to adulthood and tested for insecticide resistance using WHO bioassays.
Results: Anopheles gambiae s.s. showed a dramatic increase in kdr frequency from 1996 - 2010, coincident with the scale up of insecticide-treated nets. By 2009-2010, the kdr L1014S allele was nearly fixed in the A. gambiae s.s. population, but was absent in A. arabiensis. Near Lake Victoria, A. arabiensis was dominant in samples, while at sites north of the lake A. gambiae s.s was more common but declined relative to A. arabiensis from 2009 to 2010. Bioassays demonstrated that A. gambiae s.s. had moderate phenotypic levels of resistance to DDT, permethrin and deltamethrin while A. arabiensis was susceptible to all insecticides tested.
Conclusions: The kdr L1014S allele has approached fixation in A. gambiae s.s. populations of western Kenya, and these same populations exhibit varying degrees of phenotypic resistance to DDT and pyrethroid insecticides. The near absence of A. gambiae s.s. from populations along the lakeshore and the apparent decline in other populations suggest that insecticide-treated nets remain effective against this mosquito despite the increase in kdr allele frequency. The persistence of A. arabiensis, despite little or no detectable insecticide resistance, is likely due to behavioural traits such as outdoor feeding and/or feeding on non-human hosts by which this species avoids interaction with insecticide-treated nets.
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http://dx.doi.org/10.1186/1475-2875-10-10 | DOI Listing |
Parasit Vectors
December 2024
Laboratory of Entomology, Plant Sciences Group, Wageningen University, Wageningen, The Netherlands.
Analyses of mosquito-borne virus outbreaks have revealed the presence of similar virus strains over several years. However, it remains unclear how mosquito-borne viruses can persist over winter, when conditions are generally unfavorable for virus circulation. One potential route for virus persistence is via diapausing mosquitoes.
View Article and Find Full Text PDFObjectives: The number of mosquito bites a person receives determines the risk of acquiring malaria and the likelihood of transmitting infections to mosquitoes. We assessed heterogeneity in biting and associated factors in two settings in Uganda with different endemicity.
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Parasit Vectors
December 2024
Department of Biology, College of Arts and Sciences, Baylor University, Waco, TX, USA.
Background: The high burden of malaria in Africa is largely due to the presence of competent and adapted Anopheles vector species. With invasive Anopheles stephensi implicated in malaria outbreaks in Africa, understanding the genomic basis of vector-parasite compatibility is essential for assessing the risk of future outbreaks due to this mosquito. Vector compatibility with P.
View Article and Find Full Text PDFMalar J
December 2024
Johns Hopkins Malaria Research Institute, Baltimore, MD, 21205, USA.
Studies on Plasmodium falciparum transmission require blood-feeding infectious gametocytes to mosquitoes using standard membrane-feeding assays (SMFAs). SMFAs are routinely performed using electric heating coils or glass membrane feeders connected to a circulatory water bath using tubing and clamps. Each of these approaches is expensive and requires a complex setup, hence restricting the number of assays that can be performed simultaneously.
View Article and Find Full Text PDFMalar J
December 2024
Environmental Health and Ecological Science Department, Ifakara Health Institute, Mikocheni, Dar es Salaam, Tanzania.
Background: Effective vector control interventions, notably insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are indispensable for malaria control in Tanzania and elsewhere. However, the emergence of widespread insecticide resistance threatens the efficacy of these interventions. Monitoring of insecticide resistance is, therefore, critical for the selection and assessment of the programmatic impact of insecticide-based interventions.
View Article and Find Full Text PDFEnter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!