Experimental hut evaluation of Fendona 6SC®-treated bednets and Interceptor® long-lasting nets against Anopheles gambiae s.l. in Burkina Faso.

Background & objectives: Malaria prevention relies heavily on insecticide-treated bednets. Even though the benefits of bednets have been proven that in most of the studies carried out in Africa, their efficacy remains dependent on local conditions. In this study, under field conditions, we evaluated the efficacy of two LLINs (PermaNet® vs Interceptor®) and two bednet treatment kits (K-O TAB® vs Fendona 6SC®) against Anopheles gambiae s.l. Methods: Bednets were evaluated using experimental huts in the village of Pissy located in the Saponé health district of Burkina Faso. Treatments and sleepers were randomly rotated between huts. Results are expressed in terms of induced exophily, mortality after 24 h and blood-feeding inhibition. Results: A total of 1392 An. gambiae s.l. mosquitoes were collected during 120 nights in the experimental huts. The overall mortality rates were 85.4% (CL: 79.7–91.4) and 77.5% (CL: 56.9–97.3) for PermaNet® and Interceptor®, respectively. For the conventionally treated bednets, the mortality was 78.2% (CL: 63.13–96.7) with the Fendona 6SC®-treated nets and 75.5% (CL: 61.2–93) with the K-O TAB®-treated nets. The proportion of blood-fed mosquitoes was significantly higher in the untreated bednet arm than in the treated one, as well as for long-lasting nets than for conventionally treated nets. The entry rate did not vary significantly according to the bednet type, but the treated bednets increased the level of exophily by at least 43%. Conclusion: In the field, the Fendona 6SC® kit and the Interceptor bednets showed comparable efficacy to the already used K-O TAB® kit and PermaNet® bednets. These results could help National Malaria Program managers to formulate appropriate policy for effective vector control.

Evaluation of Field Performance of Insecticide-Treated Mosquito Nets in North-Western Burkina Faso.

Aims: The aim of the study was to evaluate the field performance of insecticide-treated mosquito nets (ITNs) in north-western Burkina Faso. Study design: Cross-sectional survey. Place and Duration: The study took place between September and November 2008 (end of rainy season) in rural north-western Burkina Faso. Methodology: Standard WHO bioassays were performed on field-collected ITNs from three areas of different insecticide pressure: semi-urban Nouna town, three villages with cotton agriculture, and three villages without cotton agriculture. Data on age and washing frequency of ITNs was collected, and deltamethrin content was determind by HPLC. Results: The mean age of field-collected ITNs was 2.1 years. The mosquito mortality rate (Anopheles gambiae sl.) after 24 hours was 4% for the negative controls, 90% for the positive controls, and 73% for field-used ITNs. Differences in mosquito mortality between sub-areas disappeared after controlling for confounding variables. Conclusion: This study demonstrates that under real life conditions, deltamethrin still shows some level of effectiveness despite ongoing insecticide pressure. However, deltamethrin resistance has been observed in other parts of the country and thus close surveillance of ITN efficacy is needed. More frequent replacement of ITNs is also recommended.

Effective population size of Anopheles funestus chromosomal forms in Burkina Faso

Background: As Anopheles funestus is one of the principal Afro-tropical malaria vectors; a more complete understanding of its population structure is desirable. In West and Central Africa; An. funestus population structure is complicated by the coexistence of two assortatively mating chromosomal forms. Effective population size (Ne) is a key parameter in understanding patterns and levels of intraspecific variation; as it reflects the role of genetic drift. Here; Ne was estimated from both chromosomal forms; Kiribina and Folonzo; in Burkina Faso. Methods: Short-term Ne was estimated by evaluating variation at 16 microsatellite loci across temporal samples collected annually from 2000-2002. Estimates were based on standardized variance in allele frequencies or a maximum likelihood method. Long-term Ne was estimated from genetic diversity estimates using mtDNA sequences and microsatellites. Results: For both forms; short-term and long-term Ne estimates were on the order of 103 and 105; respectively. Long-term Ne estimates were larger when based on loci from chromosome 3R (both inside and outside of inversions) than loci outside of this arm. Conclusion: Ne values indicate that An. funestus is not subject to seasonal bottlenecks. Though not statistically different because of large and overlapping confidence intervals; short-term Ne estimates were consistently smaller for Kiribina than Folonzo; possibly due to exploitation of different breeding sites: permanent for Folonzo and intermittent for Kiribina. The higher long-term Ne estimates on 3R; the arm carrying the two inversions mainly responsible for defining the chromosomal forms; give natural selection broader scope and merit further study