Studies were carried out at three sites in the highlands of western Kenya (Iguhu and Mbale in Kakamega and Vihiga districts, respectively, and Marani in Kisii district) and at one site in the western Kenya lowlands (Kombewa in Kisumu district) to determine the spatial-temporal dynamics of malaria vectors and intensity of malaria transmission from June 2003 to June 2004. At the highland sites, Anopheles gambiae Giles predominated, constituting >80% of the vector species, whereas An. funestus Giles made up <20%. In contrast, at the lowland site, An. funestus made up 68% of the vector species. The mean annual indoor resting densities of An. gambiae at Iguhu were 5.0 female mosquitoes per house per night, 14.2- and 26.3-fold greater than those at Mbale and Marani. During the main transmission season, the indoor resting densities of An. gambiae increased 4.1-, 10.1-, and 5.0-fold over the dry season period in Iguhu, Mbale, and Marani, respectively. The estimated annual entomological inoculation rate (EIR) at Iguhu was 16.6 infectious bites per person per year (ib/p/yr), 1.1 at Mbale, and 0.4 at Marani. This suggests high spatial variation in vector abundance and malaria transmission intensity. At the lowland site, Kombewa, the total annual EIR was 31.1 ib/p/yr and the indoor resting densities during the transmission season increased 7.1-fold in An. funestus and 18.5-fold in An. gambiae sensu lato over the dry season. The low level of transmission in the highlands suggests that it may be disrupted by vector control methods such as residual spraying.

No abstract

We sampled Anopheles funestus Giles mosquitoes from 10 sites in Kenya to determine (1) the different members of this group present at these sites and (2) the population genetic structure of these species based on chromosomal inversion karyotypes with particular reference to the role of the Eastern arm of the Great Rift Valley and geographical distance as barriers to gene flow. Four members of this species group, namely An. funestus s.s., An. parensis, An. leesoni, and An. rivulorum, were found. An. funestus was found almost exclusively inside human dwellings while An. rivulorum was found almost exclusively outdoors. An. parensis was found both indoors and outdoors in comparable proportions. Earlier attempts to collect this group of mosquitoes from two of the sites yielded no mosquitoes, suggesting that numbers of mosquitoes change during the year, sometime reaching zero or very near zero. Significant levels of differentiation were observed among some An. funestus s.s. populations studied. Results suggest that the Rift Valley acts as a barrier to gene flow for An. funestus, but that levels of differentiation are not associated with the geographical distance between populations. The results are discussed in the light of the fact that inversions may have some adaptive significance to differences in environmental conditions.

BackgroundLong Lasting Insecticidal Nets (LLIN) and Indoor Residual Spraying (IRS) have both proven to be effective malaria vector control strategies in Africa and the new technology of insecticide treated durable wall lining (DL) is being evaluated. Sustaining these interventions at high coverage levels is logistically challenging and, furthermore, the increase in insecticide resistance in African malaria vectors may reduce the efficacy of these chemical based interventions. Monitoring of vector populations and evaluation of the efficacy of insecticide based control approaches should be integral components of malaria control programmes. This study reports on entomological survey conducted in 2011 in Bomi County, Liberia.Methods Anopheles gambiae larvae were collected from four sites in Bomi, Liberia, and reared in a field insectary. Two to five days old female adult An gambiae s.l. were tested using WHO tube (n = 2027) and cone (n = 580) bioassays in houses treated with DL or IRS. A sample of mosquitoes (n = 169) were identified to species/molecular form and screened for the presence of knock down resistance (kdr) alleles associated with pyrethroid resistance.Results Anopheles gambiae s.l tested were resistant to deltamethrin but fully susceptible to bendiocarb and fenithrothion. The corrected mortality of local mosquitoes exposed to houses treated with deltamethrin either via IRS or DL was 12% and 59% respectively, suggesting that resistance may affect the efficacy of these interventions. The presence of pyrethroid resistance was associated with a high frequency of the 1014F kdr allele (90.5%) although this mutation alone cannot explain the resistance levels observed.ConclusionHigh prevalence of resistance to deltamethrin in Bomi County may reduce the efficacy of malaria strategies relying on this class of insecticide. The findings highlight the urgent need to expand and sustain monitoring of insecticide resistance in Liberian malaria vectors, evaluate the effectiveness of existing interventions and develop appropriate resistance management strategies.

No abstract