Anopheles gambiae distribution and insecticide resistance in the cities of Douala and Yaoundé (Cameroon): influence of urban agriculture and pollution

Background: Urban malaria is becoming a major health priority across Africa. A study was undertaken to assess the importance of urban pollution and agriculture practice on the distribution and susceptibility to insecticide of malaria vectors in the two main cities in Cameroon. Methods: Anopheline larval breeding sites were surveyed and water samples analysed monthly from October 2009 to December 2010. Parameters analysed included turbidity, pH, temperature, conductivity, sulfates, phosphates,nitrates, nitrites, ammonia, aluminium, alkalinity, iron, potassium, manganese, magnesium, magnesium hardness and total hardness. Characteristics of water bodies in urban areas were compared to rural areas and between urban sites. The level of susceptibility of Anopheles gambiae to 4% DDT, 0.75% permethrin, 0.05% deltamethrin, 0.1% bendiocarb and 5% malathion were compared between mosquitoes collected from polluted, non polluted and cultivated areas. Results: A total of 1,546 breeding sites, 690 in Yaoundé and 856 in Douala, were sampled in the course of the study. Almost all measured parameters had a concentration of 2- to 100-fold higher in urban compare to rural breeding sites. No resistance to malathion was detected, but bendiocarb resistance was present in Yaounde. Very low mortality rates were observed following DDT or permethrin exposure, associated with high kdr frequencies. Mosquitoes collected in cultivated areas, exhibited the highest resistant levels. There was little difference in insecticide resistance or kdr allele frequency in mosquitoes collected from polluted versus non-polluted sites. Conclusion: The data confirm high selection pressure on mosquitoes originating from urban areas and suggest urban agriculture rather than pollution as the major factor driving resistance to insecticide

Population structure of the malaria vector Anopheles moucheti in the equatorial forest region of Africa

<p>Abstract</p> <p>Background</p> <p><it>Anopheles moucheti </it>is a major malaria vector in forested areas of Africa. However, despite its important epidemiological role, it remains poorly known and insufficiently studied. Here, levels of genetic differentiation were estimated between different <it>A. moucheti </it>populations sampled throughout its distribution range in Central Africa.</p> <p>Methods</p> <p>Polymorphism at ten microsatellite markers was compared in mosquitoes sampled in Cameroon, the Democratic Republic of Congo and an island on Lake Victoria in Uganda. Microsatellite data were used to estimate genetic diversity within populations, their relative long-term effective population size, and the level of genetic differentiation between them.</p> <p>Results</p> <p>All specimens collected in Tsakalakuku (Democratic Republic of Congo) were identified as <it>A. m. bervoetsi </it>while other samples consisted of <it>A. m. moucheti</it>. Successful amplification was obtained at all microsatellite loci within all <it>A. m. moucheti </it>samples while only six loci amplified in <it>A. m. bervoetsi</it>. Allelic richness and heterozygosity were high for all populations except the island population of Uganda and <it>A. m. bervoetsi</it>. High levels of genetic differentiation were recorded between <it>A. m. bervoetsi </it>and each <it>A. m. moucheti </it>sample as well as between the island population of <it>A. m. moucheti </it>and mainland populations. Significant isolation by distance was evidenced between mainland populations.</p> <p>Conclusion</p> <p>High levels of genetic differentiation supports complete speciation of <it>A. m. bervoetsi </it>which should henceforth be recognized as a full species and named <it>A. bervoetsi</it>. Isolation by distance is the main force driving differentiation between mainland populations of <it>A. m. moucheti</it>. Genetically and geographically isolated populations exist on Lake Victoria islands, which might serve as relevant field sites for evaluation of innovative vector control strategies.</p

Population genetic structure of the malaria vector Anopheles nili in sub-Saharan Africa

<p>Abstract</p> <p>Background</p> <p><it>Anopheles nili </it>is a widespread efficient vector of human malaria parasites in the humid savannas and forested areas of sub-Saharan Africa. Understanding <it>An. nili </it>population structure and gene flow patterns could be useful for the development of locally-adapted vector control measures.</p> <p>Methods</p> <p>Polymorphism at eleven recently developed microsatelitte markers, and sequence variation in four genes within the 28s rDNA subunit (ITS2 and D3) and mtDNA (COII and ND4) were assessed to explore the level of genetic variability and differentiation among nine populations of <it>An. nili </it>from Senegal, Ivory Coast, Burkina Faso, Nigeria, Cameroon and the Democratic Republic of Congo (DRC).</p> <p>Results</p> <p>All microsatellite loci successfully amplified in all populations, showing high and very similar levels of genetic diversity in populations from West Africa and Cameroon (mean Rs = 8.10-8.88, mean He = 0.805-0.849) and much lower diversity in the Kenge population from DRC (mean Rs = 5.43, mean He = 0.594). Bayesian clustering analysis of microsatellite allelic frequencies revealed two main genetic clusters in the dataset. The first one included only the Kenge population and the second grouped together all other populations. High Fst estimates based on microsatellites (Fst > 0.118, P < 0.001) were observed in all comparisons between Kenge and all other populations. By contrast, low Fst estimates (Fst < 0.022, P < 0.05) were observed between populations within the second cluster. The correlation between genetic and geographic distances was weak and possibly obscured by demographic instability. Sequence variation in mtDNA genes matched these results, whereas low polymorphism in rDNA genes prevented detection of any population substructure at this geographical scale.</p> <p>Conclusion</p> <p>Overall, high genetic homogeneity of the <it>An. nili </it>gene pool was found across its distribution range in West and Central Africa, although demographic events probably resulted in a higher level of genetic isolation in the marginal population of Kenge (DRC). The role of the equatorial forest block as a barrier to gene flow and the implication of such findings for vector control are discussed.</p

Elimination Therapy for the Endemic Malarias

Most malaria diagnosed outside endemic zones occurs in patients experiencing the consequences of what was likely a single infectious bite by an anopheline mosquito. A single species of parasite is nearly always involved and expert opinion on malaria chemotherapy uniformly prescribes species- and stage-specific treatments. However the vast majority of people experiencing malaria, those resident in endemic zones, do so repeatedly and very often with the involvement of two or more species and stages of parasite. Silent forms of these infections—asymptomatic and beyond the reach of diagnostics—may accumulate to form substantial and unchallenged reservoirs of infection. In such settings treating only the species and stage of malaria revealed by diagnosis and not others may not be sensible or appropriate. Developing therapeutic strategies that address all species and stages independently of diagnostic evidence may substantially improve the effectiveness of the control and elimination of endemic malaria

Distribution and larval habitat characterization of Anopheles moucheti, Anopheles nili, and other malaria vectors in river networks of southern Cameroon

Despite their importance as malaria vectors, little is known of the bionomic of Anopheles nili and Anopheles moucheti. Larval collections from 24 sites situated along the dense hydrographic network of south Cameroon were examined to assess key ecological factors associated with these mosquitoes distribution in river networks. Morphological identification of the III and IV instar larvae by the use of microscopy revealed that 47.6% of the larvae belong to An. nili and 22.6% to An. moucheti. Five variables were significantly involved with species distribution, the pace of flow of the river (lotic, or lentic), the light exposure (sunny or shady), vegetation (presence or absence of vegetation) the temperature and the presence or absence of debris. Using canonical correspondence analysis. it appeared that lotic rivers. exposed to light, with vegetation or debris were the best predictors of An. nili larval abundance. Whereas, An. moucheti and An. ovengensis were highly associated with lentic rivers, low temperature, having Pistia. An. nili and An. moucheti distribution along river systems across south Cameroon was highly correlated with environmental variables. The distribution of An. nili conforms to that of a generalist species which is adapted to exploiting a variety of environmental conditions, Whereas, An. moucheti, Anopheles ovengensis and Anopheles carnevalei appeared as specialist forest mosquitoes