Detection of kdr and ace-1 mutations in wild populations of Anopheles arabiensis and An. melas in a residual malaria transmission area of Senegal.

In the central western Senegal, malaria transmission has been reduced low due to the combination of several effective control interventions. However, despite this encouraging achievement, residual malaria transmission still occurring in few areas, mainly ensured by An. arabiensis and An. melas. The resurgence or the persistence of the disease may have originated from the increase and the spread of insecticide resistance genes among natural malaria vectors populations. Therefore, assessing the status and mechanisms of insecticides resistance among targeted malaria vectors is of highest importance to better characterize factors underlying the residual transmission where it occurs. Malaria vectors were collected from three selected villages using nocturnal human landing catches (HLC) and pyrethrum spray collections (PSC) methods. An. gambiae s.l. specimens were identified at the species level then genotyped for the presence of kdr-west (L1014F), kdr-east (L1014S) and ace-1R mutations by qPCR. An. arabiensis (69.36%) and An. melas (27.99%) were the most common species of the Gambiae complex in the study area. Among An. arabiensis population, the allelic frequency of the kdr-east (22.66%) was relatively higher than for kdr-west mutation (9.96%). While for An. melas populations, the overall frequencies of both mutations were very low, being respectively 1.12% and 0.40% for the L1014S and L1014F mutations. With a global frequency of 2%, only the heterozygous form of the G119S mutation was found only in An. arabiensis and in all the study sites. The widespread occurrence of the kdr mutation in both An. arabiensis and An. melas natural populations, respectively the main and focal vectors in the central-western Senegal, may have contributed to maintaining malaria transmission in the area. Thus, compromising the effectiveness of pyrethroids-based vector control measures and the National Elimination Goal. Therefore, monitoring and managing properly insecticide resistance became a key programmatic intervention to achieve the elimination goal where feasible, as aimed by Senegal. Noteworthy, this is the first report of the ace-1 mutation in natural populations of An. arabiensis from Senegal, which need to be closely monitored to preserve one of the essential insecticide classes used in IRS to control the pyrethroids-resistant populations.

Insecticide resistance in Anopheles arabiensis populations from Dakar and its suburbs: role of target site and metabolic resistance mechanisms.

BACKGROUND: Urban malaria is an increasing concern in most of the sub-Saharan Africa countries. In Dakar, the capital city of Senegal, the malaria epidemiology has been complicated by recurrent flooding since 2005. The main vector control measure for malaria prevention in Dakar is the community use of long-lasting insecticide-treated nets. However, the increase of insecticide resistance reported in this area needs to be better understood for suitable resistance management. This study reports the situation of insecticide resistance and underlying mechanisms in Anopheles arabiensis populations from Dakar and its suburbs. RESULTS: All the populations tested showed resistance to almost all insecticides except organophosphates families, which remain the only lethal molecules. Piperonil butoxide (PBO) and ethacrinic acid (EA) the two synergists used, have respectively and significantly restored the susceptibility to DDT and permethrin of Anopheles population. Molecular identification of specimens revealed the presence of An. arabiensis only. Kdr genotyping showed the presence of the L1014F mutation (kdr-West) as well as L1014S (kdr-East). This L1014S mutation was found at very high frequencies (89.53%) in almost all districts surveyed, and in association with the L1014F (10.24%). CONCLUSION: Results showed the contribution of both target-site and metabolic mechanisms in conferring pyrethroid resistance to An. arabiensis from the flooded areas of Dakar suburbs. These data, although preliminary, stress the need for close monitoring of the urban An. arabiensis populations for a suitable insecticide resistance management system to preserve core insecticide-based vector control tools in this flooded area.

Contrasting responses to ectomycorrhizal inoculation in seedlings of six tropical African tree species.

Five caesalpinioid legumes, Afzelia africana, Afzelia bella, Anthonotha macrophylla, Cryptosepalum tetraphylum and Paramacrolobium coeruleum, and one Euphorbiaceae species, Uapaca somon, with a considerable range in seed sizes, exhibited different responses to inoculation by four species of ectomycorrhizal (ECM) fungi, Scleroderma dictyosporum, S. verrucosum, Pisolithus sp. and one thelephoroid sp. in greenhouse conditions. Thelephoroid sp. efficiently colonized seedlings of all of the five caesalpinioid legumes except U. somon, but provided no more growth benefit than the other fungi. Thelephoroid sp. and S. dictyosporum colonized seedlings of U. somon poorly, but stimulated plant growth more than the other fungi. The relative mycorrhizal dependency (RMD) values of the caesalpinioid legumes were never higher than 50%, whilst U. somon had RMD values ranging from 84.6 to 88.6%, irrespective of the fungal species. The RMD values were negatively related to seed mass for all plant species. Potassium concentrations in leaves were more closely related than phosphorus to the stimulation of seedling biomass production by the ECM fungi. Our data support the hypothesis that African caesalpinioid legumes and euphorbe tree species with smaller seeds show higher RMD values than those with the larger seeds.