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Background High coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the cornerstones of vector control strategy in Senegal where insecticide resistance by the target vectors species is a great of concern. This study explores insecticide susceptibility profile and target-site mutations mechanisms within the Anophelesgambiae complex in southeastern Senegal. Methods Larvae of Anopheles spp. were collected in two sites from southeastern Senegal Kedougou and Wassadou/Badi in October and November 2014, and reared until adult emergence. Wild F0 adult mosquitoes were morphologically identified to species. Susceptibility of 3–5-day-old An. gambiae (s.l.) samples to 11 insecticides belonging to the four insecticide classes was assessed using the WHO insecticide susceptibility bioassays. Tested samples were identified using molecular techniques and insecticide resistance target-site mutations (kdr, ace-1 and rdl) were determined. Results A total of 3742 An.gambiae (s.l.) were exposed to insecticides (2439 from Kedougou and 1303 from Wassadou-Badi). Tests with pyrethroid insecticides and DDT showed high level of resistance in both Kedougou and Wassadou/Badi. Resistance to pirimiphos-methyl and malathion was not detected while resistance to bendoicarb and fenitrothion was confirmed in Kedougou. Of the 745 specimens of An.gambiae (s.l.) genotyped, An.gambiae (s.s.) (71.6%) was the predominant species, followed by An.arabiensis (21.7%), An.coluzzii (6.3%) and hybrids (An. gambiae (s.s.)/An.coluzzii; 0.4%). All target site mutations investigated (Vgsc-1014F, Vgsc-1014S, Ace-1 and Rdl) were found at different frequencies in the species of the Anophelesgambiae complex. Vgsc-1014F mutation was more frequent in An.gambiae (s.s.) and An.coluzzii than An.arabiensis. Vgsc-1014S was present in An.gambiae (s.l.) populations in Wassadou but not in Kedougou. Ace-1 and rdl mutations were more frequent in An.gambiae (s.s.) in comparison to An.arabiensis and An.coluzzii. Conclusions Resistance to all the four insecticide classes tested was detected in southeastern Senegal as well as all target site mutations investigated were found. Data will be used by the national Malaria Control Programme.

Background Long-lasting insecticidal nets (LLINs) are the primary malaria prevention and control intervention in many parts of sub-Saharan Africa. While LLINs are expected to last at least 3 years under normal use conditions, they can lose effectiveness because they fall out of use, are discarded, repurposed, physically damaged, or lose insecticidal activity. The contributions of these different interrelated factors to durability of nets and their protection against malaria have been unclear. Methods Starting in 2009, LLIN durability studies were conducted in seven countries in Africa over 5 years. WHO-recommended measures of attrition, LLIN use, insecticidal activity, and physical integrity were recorded for eight different net brands. These data were combined with analyses of experimental hut data on feeding inhibition and killing effects of LLINs on both susceptible and pyrethroid resistant malaria vectors to estimate the protection against malaria transmission—in terms of vectorial capacity (VC)—provided by each net cohort over time. Impact on VC was then compared in hypothetical scenarios where one durability outcome measure was set at the best possible level while keeping the others at the observed levels. Results There was more variability in decay of protection over time by country than by net brand for three measures of durability (ratios of variance components 4.6, 4.4, and 1.8 times for LLIN survival, use, and integrity, respectively). In some countries, LLIN attrition was slow, but use declined rapidly. Non-use of LLINs generally had more effect on LLIN impact on VC than did attrition, hole formation, or insecticide loss. Conclusions There is much more variation in LLIN durability among countries than among net brands. Low levels of use may have a larger impact on effectiveness than does variation in attrition or LLIN degradation. The estimated entomological effects of chemical decay are relatively small, with physical decay probably more important as a driver of attrition and non-use than as a direct cause of loss of effect. Efforts to maximize LLIN impact in operational settings should focus on increasing LLIN usage, including through improvements in LLIN physical integrity. Further research is needed to understand household decisions related to LLIN use, including the influence of net durability and the presence of other nets in the household.

Background From 2011 to 2014, an indoor residual spray (IRS) programme for malaria vectors control was implemented in six health districts in Senegal. The main objective of the present study was to evaluate the efficacy of bendiocarb (FICAM WP 80) sprayed on different wall surfaces and its impact on malaria vectors. The entomological monitoring activities were carried out monthly in five treated sentinel villages and one control untreated village in each district. Methods The residual efficacy of bendiocarb applied at a dosage of 0.4 g/sq m was monitored for a period up to 9 months post-IRS using WHO cone bioassay method. This assay consisted to expose 2–5 days old unfed susceptible Anopheles coluzzii females to sprayed walls for a period of 30 min. The mortality rates after 24 h post-exposure were estimated and compared between the different types of walls sprayed in each sentinel village. Results The results showed that the residual efficacy varied between the different sprayed walls, from one sentinel village to another and between the different campaigns. The FICAM had a residual efficacy of 3–6 months post-IRS on mud and cement wall surfaces. In some cases, the observed mortality rates were much higher than those reported elsewhere particularly during the first campaign in all the six districts. Conclusions The FICAM was found to be effective with a residual efficacy varying from 3 to 6 months. If the quality of the IRS application is excluded as a possible explanation of the short efficacy duration, the results suggest at least two rounds of treatments in order to cover the rainy season that lasts 5 to 6 months in the area. Such treatments could be carried out before the intensification of the rains in July and August in order to better cover the transmission period that occurs between late August and October in the area.

The implementation of effective malaria control strategies in the central-western Senegal, such as Indoor Residual Spraying (IRS), long-lasting insecticide-treated nets (LLIN), Seasonal malaria chemoprophylaxis (SMC) and appropriate management of malaria cases, has led to the decline of malaria transmission in the region. However, residual malaria transmission still occurring in some localities, known as hotspots villages, making challenging the achievement of the malaria elimination goal. A pilot study was undertaken between 2013 and 2014 to test the feasibility of a community-based IRS approach for malaria elimination in four targeted health districts of the Central Western Senegal.The residual efficacy of the Actellic® 300CS formulation on the sprayed surface was monitored using WHO cone test.Overall, 615 walls were tested over the two successive years, respectively 240 and 375 in 2013 and 2014 IRS campaigns. The residual efficacy of the IRS with Actellic®300 CS was longer in the second year due to the improvement of community agents spraying skill the second year thanks to the refreshing training and a better supervision by professional agent of the National Hygiene Service. The analysis of the Incidence Rate Ratio under the Poisson model shows no significant difference of IRS effectiveness according to the building type.In conclusion, the quality of training of community agents and good supervision of IRS activities play a key role in the quality and the residual efficacy of IRS campaigns. A good planning and implementation of IRS campaign ensure a high quality and a good effectiveness of spraying with the Actellic®300 CS formulation. Keywords: Malaria, Elimination, IRS, Hotspots, Community agents, 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.

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.

Background Scaling-up of effective anti-malarial control strategies in Central-West region of Senegal has resulted in the sharp decline in malaria prevalence in this area. However, despite these strategies, residual malaria transmission has been observed in some villages (hot spots). The objective of this study was to assess the impact of indoor residual spraying (IRS) with pirimiphos-methyl on malaria transmission in hot spot areas. Methods The malaria vector population dynamics were monitored in each of the six selected villages (4 of which used IRS, 2 were unsprayed control areas) using overnight human landing catches (HLC) and pyrethrum spray catches (PSC). The host source of blood meals from freshly fed females collected using PSC was identified using the direct ELISA method. Females caught through HLC were tested by ELISA for the detection of Plasmodium falciparum circumsporozoite protein and Anopheles gambiae complex was identified using PCR. Results Preliminary data shown that the densities of Anopheles populations were significantly lower in the sprayed areas (179/702) compared to the control. Overall, malaria transmission risk was 14 times lower in the intervention zone (0.94) compared to the control zone (12.7). In the control areas, three Anopheles species belonging to the Gambiae complex (Anopheles arabiensis, Anopheles coluzzii and Anopheles melas) maintained the transmission, while only An. coluzzii was infective in the sprayed areas. Conclusion The preliminary data from this pilot study showed that IRS with the CS formulation of pirimiphos-methyl is likely very effective in reducing malaria transmission risk. However, additional studies including further longitudinal entomological surveys as well as ecological and ethological and genetical characterization of vectors species and their populations are needed to better characterize the entomological impact of indoor residual spraying with pirimiphos-methyl in the residual transmission areas of Senegal.

International audience; Active catches of adult females of Aedes vexans arabiensis Patton, (Diptera: Culicidae) Patton by nets or aspirator, were conducted in 2003 and 2004 in the vegetation at the edge of temporary ponds in Barkedji, Senegalese Ferlo area. Two hundred and forty-one engorged females were captured, dissected and the gut content adsorbed on a Whatman filter paper and analysed using the enzyme-linked immunosorbent assay (ELISA) technique to determinate the bloodmeal origin. Results indicated that Ae v. arabiensis fed primarily on mammals, including horses (35.7% of the bloodmeals), but also on birds (10%). Moreover, associations between horses and birds accounted for 42% of the mixed bloodmeals. These results show an opportunistic feeding behaviour and suggest that Ae v. arabiensis is a probable vector bridging the West Nile virus between horses and birds hosts in the Ferlo area.

Des etudes entomologiques realisees en zone de mangrove dans des villages situes dans le delta du Saloum, de juin 1995 a janvier 1998, ont permis de mieux comprendre la contribution d'An. melas Theobald (1903) dans la transmission du paludisme cotier. Parmi les cinq villages prospectes, trois : Simal, Djilor et Marlothie sont en bordure du fleuve Saloum ; les deux autres : Djifere et Diakhanor sont situes entre l'ocean et le fleuve. Dans cette zone cotiere, An. melas vit en sympatrie avec An. arabiensis et les proportions de ces deux especes varient suivant la position des villages par rapport a la ligne de mangrove et en relation avec les saisons. Dans les trois villages situes en bordure du fleuve Saloum, An. arabiensis predomine. Dans les deux villages situes sur le littoral,, An. melas predomine. L'endophagie, l'endophilie et l'anthropophile sont tres nettes chez An. melas dans cette zone ou il predomine. La transmission palustre s'effectue de juillet a mars avec un maximum en debut de saison seche. En periode de sympatrie, An. arabiensis est responsable de la transmission et lorsqu'il est absent, ce role revient a An. melas . L'intensite de la transmission, bien que faible, est comparable dans les trois villages du delta a predominance An. arabiensis et dans les deux villages du littoral a predominance An. melas . An. melas etait tres anthropophile dans la zone du littoral mais s'infectait faiblement du fait d'une longevite tres reduite.

Background The study of vector feeding behaviour is an important step in the understanding of the epidemiology of vector borne diseases. The main objective of this work was to study the spatio-temporal host preferences and blood-feeding patterns of malaria vectors in a pastoral area of Senegal where cattle breeding is the main human activity. Methods Malaria vectors were collected indoors by pyrethrum spray catch in 16 villages belonging to 4 different landscape classes (wooded savanna, shrubby savanna, bare soils and steppe). Blood meals sources were determined using a direct enzyme-linked immunosorbent assay (ELISA). Results The blood meal origins of 1886 freshly fed An. gambiae s.l. were determined. Among these blood meals, most were taken on a single host: 40.1% on human and 37.1% on animal. The range in proportions of blood meals taken from human were 25–62.4% in wooded savanna villages, 23.5–61.9% in shrubby savanna villages, 31.3–70% in bare soils villages and 57.7–68.7 in steppe villages. Blood meals taken from bovines were very heterogeneous with two clusters localized in the Northeast and Southwest axis of the study area that corresponds to the distribution of the main water ponds. Patent mixed blood meals taken from human and non-human were significantly higher than those taken from two animals, the highest proportions being observed in September (shrubby savanna, bare soils and steppe villages) or October (wooded savanna villages). Conclusions These observations suggest that in this pastoral area, differences in feeding patterns of malaria vectors are merely linked to the specific localization of villages and are not influenced by landscape class distribution. In addition, the temporal variations in the anthropophilic rates are influenced by the presence of standing water in the study area.

In high endemicity areas, malaria is a chronic disease: examination of blood films reveals that up to half of the population, particularly children, harbour parasites at any one given time. The parasitological status of the remainder was addressed using the polymerase chain reaction, a technique 100 to 1000 times more sensitive than microscopy, on a series of samples from Dielmo, a holoendemic area of Senegal. Two-thirds of the microscopically negative individuals were found to harbour subpatent levels of Plasmodium falciparum, suggesting that more than 90% of the exposed population at any one time, i.e. in a cross-sectional survey, are chronically infected. This also means that the range of parasite loads harboured by humans with various degrees of exposure is remarkably large, probably reflecting a large range of effectiveness of the defence mechanisms against malaria parasites, none of which is fully efficient.

In human populations, the concomitance of various parasitic infections can induce modifications of the specific immune response to each pathogen and thus induce changes in their clinical expression. Several studies, however, have produced conflicting results. To study the hypothesis that there is an association between helminthiasis and the occurrence of severe malaria a prospective case-control study was carried out in a rural zone of Senegal where 105 presumptive severe malaria attacks were studied in 2001 and 2002. Following parasitological control the cases were divided into two groups: A (severe malaria) with severe symptoms and parasite density >5000 parasites/microl (n = 64) and B (other causes) with severe symptoms and negative or weak parasite density (n = 41). In group A the prevalence of Ascaris lumbricoides infection was higher in cases of severe malaria than in controls, odds ratio (OR) = 9.95 (95% CI 3.03-32.69). Similar but not significantly different results were observed between patients in group B and their controls, OR = 2.47 (95% CI 0.95-6.38).

Background Two concomitant dengue 3 (DEN-3) epidemics occurred in Cape Verde Archipelago and Senegal between September and October 2009. Aedes aegypti was identified as the vector of these epidemics as several DEN-3 virus strains were isolated from this species in both countries. The susceptibility to pyrethroids, organochlorine, organophosphates and carbamate was investigated in two field strains of Aedes aegypti from both countries using WHO diagnostic bioassay kits in order to monitor their the current status of insecticide susceptibility. Findings The two tested strains were highly resistant to DDT. The Cape Verde strain was found to be susceptible to all others tested insecticides except for propoxur 0.1%, which needs further investigation. The Dakar strain was susceptible to fenitrothion 1% and permethrin 0.75%, but displayed reduced susceptibility to deltamethrin, lambda-cyhalothrin and propoxur. Conclusions As base-line results, our observations stress a careful management of insecticide use for the control of Ae. aegypti. Indeed, they indicate that DDT is no longer efficient for the control of Ae. aegypti populations in Cape Verde and Dakar and further suggest a thorough follow-up of propoxur susceptibility status in both sites and that of deltamethrin and lambda-cyhalothrin in Ae. aegypti populations in Dakar. Thus, regular monitoring of susceptibility is greatly needed as well as the knowing if this observed resistance/susceptibility is focal or not and for observed resistance, the use of biochemical methods is needed with detailed comparison of resistance levels over a large geographic area. Keywords Aedes aegypti, Insecticides, Susceptibility, Cape Verde, Senegal

Background Anopheles funestus is one of the major malaria vectors in tropical Africa. Because of several cycles of drought events that occurred during the 1970s, this species had disappeared from many parts of sahelian Africa, including the Senegal River basin. However, this zone has been re-colonized during the last decade by An. funestus, following the implementation of two dams on the Senegal River. Previous studies in that area revealed heterogeneity at the biological and chromosomal level among these recent populations. Methods Here, we studied the genetic structure of the newly established mosquito populations using eleven microsatellite markers in four villages of the Senegal River basin and compared it to another An. funestus population located in the sudanian domain. Results Our results presume Hardy Weinberg equilibrium in each An. funestus population, suggesting a situation of panmixia. Moreover, no signal from bottleneck or population expansion was detected across populations. The tests of genetic differentiation between sites revealed a slight but significant division into three distinct genetic entities. Genetic distance between populations from the Senegal River basin and sudanian domain was correlated to geographical distance. In contrast, sub-division into the Senegal River basin was not correlated to geographic distance, rather to local adaptation. Conclusions The high genetic diversity among populations from Senegal River basin coupled with no evidence of bottleneck and with a gene flow with southern population suggests that the re-colonization was likely carried out by a massive and repeated stepping-stone dispersion starting from the neighboring areas where An. funestus endured.

Background Mass treatment with ivermectin controls onchocerciasis as a public health problem, but it was not known if it could also interrupt transmission and eliminate the parasite in endemic foci in Africa where vectors are highly efficient. A longitudinal study was undertaken in three hyperendemic foci in Mali and Senegal with 15 to 17 years of annual or six-monthly ivermectin treatment in order to assess residual levels of infection and transmission, and test whether treatment could be safely stopped. This article reports the results of the final evaluations up to 5 years after the last treatment. Methodology/Principal Findings Skin snip surveys were undertaken in 131 villages where 29,753 people were examined and 492,600 blackflies were analyzed for the presence of Onchocerca volvulus larva using a specific DNA probe. There was a declining trend in infection and transmission levels after the last treatment. In two sites the prevalence of microfilaria and vector infectivity rate were zero 3 to 4 years after the last treatment. In the third site, where infection levels were comparatively high before stopping treatment, there was also a consistent decline in infection and transmission to very low levels 3 to 5 years after stopping treatment. All infection and transmission indicators were below postulated thresholds for elimination. Conclusion/Significance The study has established the proof of principle that onchocerciasis elimination with ivermectin treatment is feasible in at least some endemic foci in Africa. The study results have been instrumental for the current evolution from onchocerciasis control to elimination in Africa., Author Summary The control of onchocerciasis, or river blindness, is based on annual or six-monthly treatment with ivermectin of populations at risk. This has been effective in controlling the disease as a public health problem but it was not known whether it could also eliminate infection and transmission to the extent that treatment could be safely stopped. Many doubted that this was feasible in Africa. A study was undertaken in three hyperendemic onchocerciasis foci with seasonal transmission in Mali and Senegal where treatment has been given for 15 to 17 years. As a result of this treatment, infection and transmission levels had fallen everywhere below postulated thresholds for elimination. Treatment was therefore stopped in each focus. Follow-up evaluations up to 5 years after the last treatment showed no evidence of recrudescence after stopping treatment but instead a consistent decline in infection and transmission levels, reaching zero in two sites. The study has established the proof-of-principle that onchocerciasis elimination with ivermectin treatment is feasible in at least some endemic foci in Africa. The results of the study have greatly contributed to the current evolution from onchocerciasis control to elimination in Africa.

An immunomodulatory role of arthropod saliva has been well documented, but evidence for an effect on Plasmodium sp. infectiousness remains controversial. Mosquito saliva may orient the immune response toward a Th2 profile, thereby priming a Th2 response against subsequent antigens, including Plasmodium . Orientation toward a Th1 versus a Th2 profile promotes IgG and IgE proliferation, respectively, where the former is crucial for the development of an efficient antiparasite immune response. Here we assessed the direct effect of mosquito bites on the density of Plasmodium falciparum asexual parasites and the prevalence of gametocytes in chronic, asymptomatic infections in a longitudinal cohort study of seasonal transmission. We additionally correlated these parasitological measures with IgE and IgG antiparasite and anti-salivary gland extract titers. The mosquito biting density was positively correlated with the asexual parasite density but not asexual parasite prevalence and was negatively correlated with gametocyte prevalence. Individual anti-salivary gland IgE titers were also negatively correlated with gametocyte carriage and were strongly positively correlated with antiparasite IgE titers, consistent with the hypothesis that mosquito bites predispose individuals to develop an IgE antiparasite response. We provide evidence that mosquito bites have an impact on asymptomatic infections and differentially so for the production of asexual and sexual parasites. An increased research focus on the immunological impact of mosquito bites during asymptomatic infections is warranted, to establish whether strategies targeting the immune response to saliva can reduce the duration of infection and the onward transmission of the parasite.

a b s t r a c t Malaria immunity is modulated by many environmental and epidemiological factors. This study evaluates the influence of a hitherto unstudied environmental-epidemiological fac- tor, namely the impact of human exposure to Anopheles bites on the isotype profile of acquired antibody responses to Plasmodium falciparum. In two Senegalese villages where the intensity of exposure to Anopheles bites was markedly different (high and low exposure), specific IgG1 and IgG3 responses to P. falciparum whole schizont extract (WSE) and circum- sporozoite protein (CSP) were evaluated at the peak of Anopheles exposure (September) and later (December) in a cohort of 120 children aged 3-8 years. Multivariate analysis showed a significantly lower IgG1 response against P. falciparum WSE and CSP in children highly exposed to Anopheles bites (Gankette) compared to those who were weakly exposed (Mboula). In contrast, in both villages, parasitemia and increasing age were strongly asso- ciated with higher IgG1 and IgG3 levels. We hypothesize that high exposure to Anopheles bites could inhibit IgG1-dependent responsiveness to P. falciparum known to induce protec- tive immune responses against malaria. The impact of mosquito saliva on the regulation of specific protective immunity may need to be taken into account in epidemiological studies and trials for malaria vaccines.

Background The evaluation of malaria transmission intensity is a crucial indicator for estimating the burden of malarial disease. In this respect, entomological and parasitological methods present limitations, especially in low transmission areas. The present study used a sensitive multiplex assay to assess the exposure to Plasmodium falciparum infection in children living in an area of low endemicity. In three Senegalese villages, specific antibody (IgG) responses to 13 pre-erythrocytic P. falciparum peptides derived from Lsa1, Lsa3, Glurp, Salsa, Trap, Starp, Csp and Pf11.1 proteins were simultaneously evaluated before (June), at the peak (September) and after (December) the period of malaria transmission, in children aged from 1 to 8 years. Results Compared to other antigens, a high percentage of seropositivity and specific antibody levels were detected with Glurp, Salsa1, Lsa3NR2, and Lsa1J antigens. The seropositivity increased with age for all tested antigens. Specific IgG levels to Glurp, Salsa1, Lsa3NR2, and Lsa1J were significantly higher in P. falciparum infected children compared to non-infected and this increase is significantly correlated with parasite density. Conclusion The multiplex assay represents a useful technology for a serological assessment of rapid variations in malaria transmission intensity, especially in a context of low parasite rates. The use of such combined serological markers (i.e. Glurp, Lsa1, Lsa3, and Salsa) could offer the opportunity to examine these variations over time, and to evaluate the efficacy of integrated malaria control strategies.

Background The different taxa belonging to Anopheles gambiae complex display phenotypic differences that may impact their contribution to malaria transmission. More specifically, their susceptibility to infection, resulting from a co-evolution between parasite and vector, might be different. The aim of this study was to compare the susceptibility of M and S molecular forms of Anopheles gambiae and Anopheles arabiensis to infection by Plasmodium falciparum. Methods F3 progenies of Anopheles gambiae s.l. collected in Senegal were infected, using direct membrane feeding, with P. falciparum gametocyte-containing blood sampled on volunteer patients. The presence of oocysts was determined by light microscopy after 7 days, and the presence of sporozoite by ELISA after 14 days. Mosquito species and molecular forms were identified by PCR. Results The oocyst rate was significantly higher in the molecular S form (79.07%) than in the M form (57.81%, Fisher's exact test p < 0.001) and in Anopheles arabiensis (55.38%, Fisher's exact test vs. S group p < 0.001). Mean ± s.e.m. number of oocyst was greater in the An. gambiae S form (1.72 ± 0.26) than in the An. gambiae M form (0.64 ± 0.04, p < 0.0001) and in the An. arabiensis group (0.58 ± 0.04, vs. S group, p < 0.0001). Sporozoite rate was also higher in the molecular form S (83.52%) than in form M (50.98%, Fisher's exact test p < 0.001) and Anopheles arabiensis 50.85%, Fisher's exact test vs. S group p < 0.001). Conclusion Infected in the same experimental conditions, the molecular form S of An. gambiae is more susceptible to infection by P. falciparum than the molecular form M of An. gambiae and An. arabiensis.

The Research Center for Human Development in Dakar (CRDH) with the technical assistance of ICF Macro and the National Malaria Control Programme (NMCP) conducted in 2008/2009 the Senegal Malaria Indicator Survey (SMIS), the first nationally representative household survey collecting parasitological data and malaria-related indicators. In this paper, we present spatially explicit parasitaemia risk estimates and number of infected children below 5 years. Geostatistical Zero-Inflated Binomial models (ZIB) were developed to take into account the large number of zero-prevalence survey locations (70%) in the data. Bayesian variable selection methods were incorporated within a geostatistical framework in order to choose the best set of environmental and climatic covariates associated with the parasitaemia risk. Model validation confirmed that the ZIB model had a better predictive ability than the standard Binomial analogue. Markov chain Monte Carlo (MCMC) methods were used for inference. Several insecticide treated nets (ITN) coverage indicators were calculated to assess the effectiveness of interventions. After adjusting for climatic and socio-economic factors, the presence of at least one ITN per every two household members and living in urban areas reduced the odds of parasitaemia by 86% and 81% respectively. Posterior estimates of the ORs related to the wealth index show a decreasing trend with the quintiles. Infection odds appear to be increasing with age. The population-adjusted prevalence ranges from 0.12% in Thillé-Boubacar to 13.1% in Dabo. Tambacounda has the highest population-adjusted predicted prevalence (8.08%) whereas the region with the highest estimated number of infected children under the age of 5 years is Kolda (13940). The contemporary map and estimates of malaria burden identify the priority areas for future control interventions and provide baseline information for monitoring and evaluation. Zero-Inflated formulations are more appropriate in modeling sparse geostatistical survey data, expected to arise more frequently as malaria research is focused on elimination.

Background West Nile virus (WNV) is a widespread pathogen maintained in an enzootic cycle between mosquitoes and birds with occasional spill-over into dead-end hosts such as horses and humans. Migratory birds are believed to play an important role in its dissemination from and to the Palaearctic area, as well as its local dispersion between wintering sites. The Djoudj Park, located in Senegal, is a major wintering site for birds migrating from Europe during the study period (Sept. 2008- Jan. 2009). In this work, we studied the seasonal feeding behaviour dynamics of the potential WNV mosquito vectors at the border of the Djoudj Park, using a reference trapping method (CDC light CO2-baited traps) and two host-specific methods (horse- and pigeon-baited traps). Blood meals of engorged females were analysed to determine their origin. Results Results indicated that Culex tritaeniorhynchus and Cx. neavei may play a key role in the WNV transmission dynamics, the latter being the best candidate bridging-vector species between mammals and birds. Moreover, the attractiveness of pigeon- and horse-baited traps for Cx. neavei and Cx. tritaeniorhynchus varied with time. Finally, Cx. tritaeniorhynchus was only active when the night temperature was above 20°C, whereas Cx. neavei was active throughout the observation period. Conclusions Cx. neavei and Cx. tritaeniorhynchus are the main candidate vectors for the transmission of WNV in the area. The changes in host attractiveness might be related to variable densities of the migratory birds during the trapping period. We discuss the importance of these results on the risk of WNV transmission in horses and humans.

Background Various methods have been studied as replacement of human landing catches (HLC) for mosquito sampling in entomological studies on malaria transmission. Conflicting results have been obtained in comparing relative efficiency of alternative methods, according to the area, the species present and their density. The aim of this study was to compare the number and characteristics of mosquitoes sampled in two areas of Senegal by three different methods: HLC, light traps adjacent to an occupied bed net (LT/N), pyrethrum spray catches (PSC). Methods Collections were performed in two villages: Dielmo (Soudan savanna) and Bandafassi (Soudan Guinean savanna), two or three nights per month for a 4-5 months period during the maximal transmission season in 2001-2002. Species were identified and Plasmodium infection determined by ELISA. The specific composition, circumsporozoite protein rate and entomological inoculation rate were calculated. Results The diversity of mosquito species captured was maximal with LT/N, minimal with PSC. The mean number of anopheles captures each night was significantly different according to the method used and the species. PSC displayed a significantly lower anopheles density. HLC was the most efficient sampling method when Anopheles gambiae was the main vector (in Bandafassi); LT/N when it was Anopheles funestus (in Dielmo). A significant correlation was found between HLC and LT/M but correlation parameters were different according to the species. Circumsporozoite protein rates were not significantly different between methods or species. The entomological inoculation rate varied along with vector density and thus with methods and species. Conclusions The choice of sampling method influenced entomological data recorded. Therefore, the sampling technique has to be chosen according to the vector studied and the aim of the study. Only HLC must be considered as the reference method, but in some conditions LT/N can be used as an alternative method.

Insect-borne diseases represent a worldwide threat. In addition to fight against vectors (insecticides) and disease prevention (vaccination against yellow fever, chemoprophylaxis against malaria), insect repellents applied on the skin could help reduce the heavy burden related to these diseases. In a field study performed in Senegal, we compared the efficacy of one skin application between 3 and 4 p.m. of four spray repellents [icaridine 20%, para-menthane-diol (PMD) 20% and 50% and DEET 50%] against placebo, among 100 healthy male and female volunteers experienced with mosquito capture. Double-blind randomized cross-over placebo-controlled study (Latin-square design) during five consecutive nights (7 p.m. to midnight) in two villages was conducted. To avoid residual effect, right or left leg was alternately exposed during consecutive nights and the exposed leg was washed before next night. The statistical model was random and mixed effects ANOVA. All four active repellents provided a significant and similar protection compared with placebo, lasting 8 h. However, there was a non-significant trend for a higher protection by DEET 50% than by PMD 20% (P = 0.07). Duration of protection was similar for all repellents. Their effects were similar among men and women, and against Anopheles or other species. No serious adverse drug reaction was noticed. Using a rigorous methodology and a large number of volunteers, our well-controlled study demonstrated an important and similar protective effect of all four repellents compared with placebo. Such field studies should be required before approval of any newly developed repellent.

Background The geographic and temporal distribution of M and S molecular forms of the major Afrotropical malaria vector species Anopheles gambiae s.s. at the western extreme of their range of distribution has never been investigated in detail. Materials and methods Collections of indoor-resting An. gambiae s.l. females were carried out along a ca. 400 km west to east transect following the River Gambia from the western coastal region of The Gambia to south-eastern Senegal during 2005 end of rainy season/early dry season and the 2006 rainy season. Specimens were identified to species and molecular forms by PCR-RFLP and the origin of blood-meal of fed females was determined by ELISA test. Results Over 4,000 An. gambiae s.l. adult females were collected and identified, 1,041 and 3,038 in 2005 and 2006, respectively. M-form was mainly found in sympatry with Anopheles melas and S-form in the western part of the transect, and with Anopheles arabiensis in the central part. S-form was found to prevail in rural Sudan-Guinean savannah areas of Eastern Senegal, in sympatry with An. arabiensis. Anopheles melas and An. arabiensis relative frequencies were generally lower in the rainy season samples, when An. gambiae s.s. was prevailing. No large seasonal fluctuations were observed for M and S-forms. In areas where both M and S were recorded, the frequency of hybrids between them ranged from to 0.6% to 7%. Discussion The observed pattern of taxa distribution supports the hypothesis of a better adaptation of M-form to areas characterized by water-retaining alluvial deposits along the Gambia River, characterized by marshy vegetation, mangrove woods and rice cultivations. In contrast, the S-form seems to be better adapted to free-draining soil, covered with open woodland savannah or farmland, rich in temporary larval breeding sites characterizing mainly the eastern part of the transect, where the environmental impact of the Gambia River is much less profound and agricultural activities are mainly rain-dependent. Very interestingly, the observed frequency of hybridization between the molecular forms along the whole transect was much higher than has been reported so far for other areas. Conclusion The results support a bionomic divergence between the M and S-forms, and suggest that the western extreme of An. gambiae s.s. geographical distribution may represent an area of higher-than-expected hybridization between the two molecular forms.

Background In sub-Saharan areas, malaria transmission was mainly ensured by Anopheles. gambiae s.l. and Anopheles. funestus vectors. The immune response status to Plasmodium falciparum was evaluated in children living in two villages where malaria transmission was ensured by dissimilar species of Anopheles vectors (An. funestus vs An. gambiae s.l.). Methods A multi-disciplinary study was performed in villages located in Northern Senegal. Two villages were selected: Mboula village where transmission is strictly ensured by An. gambiae s.l. and Gankette Balla village which is exposed to several Anopheles species but where An. funestus is the only infected vector found. In each village, a cohort of 150 children aged from one to nine years was followed during one year and IgG response directed to schizont extract was determined by ELISA. Results Similar results of specific IgG responses according to age and P. falciparum infection were observed in both villages. Specific IgG response increased progressively from one-year to 5-year old children and then stayed high in children from five to nine years old. The children with P. falciparum infection had higher specific antibody responses compared to negative infection children, suggesting a strong relationship between production of specific antibodies and malaria transmission, rather than protective immunity. In contrast, higher variation of antibody levels according to malaria transmission periods were found in Mboula compared to Gankette Balla. In Mboula, the peak of malaria transmission was followed by a considerable increase in antibody levels, whereas low and constant anti-malaria IgG response was observed throughout the year in Gankette Balla. Conclusion This study shows that the development of anti-malaria antibody response was profoundly different according to areas where malaria exposure is dependent with different Anopheles species. These results are discussed according to i) the use of immunological tool for the evaluation of malaria transmission and ii) the influence of Anopheles vectors species on the regulation of antibody responses to P. falciparum.

Following the implementation of two dams in the Senegal River, entomological and parasitological studies were conducted in three different ecological zones in the Senegal River Basin (the low valley of Senegal River, the Guiers Lake area and the low valley of Ferlo) every 3 month in June 2004, September 2004, December 2004 and March 2005. The objective of this work was to study the influence of environmental heterogeneities on vector bionomics and malaria epidemiology. Mosquitoes were collected when landing on human volunteers and by pyrethrum spray catches. In the parasitological survey, blood samples were taken from a cohort of schoolchildren under 9 years during each entomology survey. Seven anopheline species were collected: Anopheles arabiensis, Anopheles gambiae M form, Anopheles funestus, Anopheles pharoensis, Anopheles coustani, Anopheles wellcomei and Anopheles rufipes. A. arabiensis, A. funestus and A. pharoensis were predominant in the low valley of the Senegal River, A. funestus in the Guiers Lake area and A. arabiensis in the low valley of Ferlo. Mosquito populations' dynamics varied temporally depending on the rainy season for each zone. The anthropophilic rates varied between 6 and 76% for A. gambiae s.l. and 23 and 80% for A. funestus. Only 4/396 A. pharoensis and 1/3076 A. funestus tested carried Plasmodium falciparum CS antigen. These results suggest the implication of A. pharoensis in malaria transmission. The related entomological inoculation rates were estimated to 10.44 in Mbilor and 3 infected bites in Gankette Balla and were due, respectively, to A. pharoensis and A. funestus. Overall, 1636 thick blood smears were tested from blood samples taken from schoolchildren with, respectively, a parasite and gametocyte average prevalence of 9 and 0.9%. The parasite prevalence was uniformly low in Mbilor and Gankette Balla whereas; it increased in September (16%) and then remained stable in December and March (22%) in Mboula where malaria transmission was not perceptible. However, significant differences were observed over time for parasite prevalence in Mbilor and Mboula villages whereas; it was only in Gankette Balla village where gametocyte prevalence was significantly different over time. Our study demonstrates the influence of ecological changes resulted from dams implementation in the Senegal River on the composition of vectorial system, malaria transmission and epidemiology. Such changes should be thoroughly surveyed in order to prevent any possible malaria outbreak in the Senegal River Basin.

This study of malaria biodiversity in Senegal used an entomological approach that combined parasite surveys and clinical investigations in the mangrove area of the Saloum delta from 1996 to 1998. The parasitologic studies took place in two of the six villages in the coastal area of Palmarin (Djifère and Diakhanor) during three distinct periods: at the end of the dry season, in the middle of the rainy season, and at the end of the rainy season. The clinical investigations at the Palmarin health station took place from July 1996 through February 1998. A malaria attack was defined as the presence of malaria symptoms (including fever, headaches, sweating, and shivering) associated with plasmodic parasitemia3,000 trophozoites/microL of blood. All the positive thick smears were infected with Plasmodium falciparum, one also with P. falciparum, and none with P. ovale. The average plasmodic index (5.6%) classifies the delta of Saloum as a hypoendemic area. The average parasite load was estimated at 2,239 trophozoites (95% CI: 1,660-3,020) of P. falciparum per microliter of blood, and 86.9% of patients with symptoms of a malaria attack were febrile. Malaria attacks accounted for 1.9% of the total consultations, 12.2% of the presumed malaria cases, and 14.0% of the febrile subjects. The finding that malaria attacks affected all age groups confirms the weakness of anti-malaria immunity among the population of the Saloum delta. Malaria cases were more frequent at the end of the rainy season and the beginning of the dry season, periods when parasite loads were highest. In this area, which is increasingly attractive to tourists and has a quite superficial fresh water table, man-made environmental changes favor mosquito breeding sites that promote the development of An. arabiensis and An. gambiae spp, both known to be major malaria vectors. In view of the population's weak anti-malaria immunity, this situation may increase malaria transmission and could be followed by epidemics. It is therefore important to set up a functional system of epidemiological monitoring to detect any malaria outbreaks.

A comparative study of human-landing catches (HLCs) and odor-baited entry traps (OBETs) for sampling malaria vectors was conducted in two different bioclimatic areas of Senegal, the Sahelian and Sudano-Guinean phytogeographic zones, from September to December 2002. Mosquitoes were collected by the two methods both indoors and outdoors. The reliability of OBET samples was tested by comparing the two methods. Overall, HLC was more effective indoors and for surveying the anopheline fauna. Both methods were effective in sampling the four known malaria vectors in Senegal [Anopheles gambiae s.s., An. arabiensis Patton, An. funestus Giles, and An. nili (Theobald) ], and mosquito age structures and infectivity rates did not differ between methods.

The Anopheles gambiae species complex includes at least seven morphologically indistinguishable species, one of which, Anopheles gambiae sensu stricto, is the primary mosquito vector responsible for the transmission of malaria across sub-Saharan Africa. Sympatric ecological diversification of An. gambiae s.s. is in progress within this complex, leading to the emergence of at least two incipient species (the M and S molecular forms now recognized as good species and named An. coluzzii and An. gambiae respectively) that show heterogeneous levels of divergence in most parts of Africa. However, this process seems to have broken down in coastal areas of West Africa at the extreme edge of the distribution. We undertook a longitudinal study to describe An. gambiae s.s. populations collected from two inland transects with different ecological characteristics in south-eastern Senegal. Analysis of samples collected from 20 sites across these two transects showed the M and S molecular forms coexisted at almost all sampled sites. Overall, similar hybridization rates (2.16% and 1.86%) were recorded in the two transects; sites with relatively high frequencies of M/S hybrids (up to 7%) were clustered toward the north-western part of both transects, often near urban settings. Estimated inbreeding indices for this putative speciation event varied spatially (range: 0.52-1), with hybridization rates being generally lower than expected under panmictic conditions. Such observations suggest substantial reproductive isolation between the M and S molecular forms, and further support the ongoing process of speciation in these inland areas. According to a recent reclassification of the An. gambiae complex, the M and S molecular forms from this zone correspond to An. coluzzii and An. gambiae, respectively. There is considerable evidence that these molecular forms differ in their behavioural and ecological characteristics. Detailed study of these characteristics will allow the development and implementation of better insect control strategies for combating malaria.

Three villages in the Senegal River basin were selected to study the biting and resting behavior of #Anopheles gambiae$ s.l. in relation to human habits, rainfalls, and rice culture irrigation. All inhabitants sleep outside throughout the year, mainly under poor quality bednets. Mosquitoes were collected host-seeking during the night on human bait outside and resting during the day inside and outside in pit shelters. #An. gambiae$ s.s. and #An. arabiensis$ fed mainly outside, the only place where hosts are available ; fed and gravid females resting indoors fed outside. The proportions of #An. gambiae$ s.s. and #An. arabiensis$ in outdoor biting catches and in indoor spray catches were not significantly different, but they differed from year to year with the latter sampling method. #An. gambiae$ s.s. predominated in 1990, a more wet and humid year, whereas #An. arabiensis$ was more common in 1991, which was an arid year. Both species are highly endophilic in this arid area where outdoor-resting places are limited. (Résumé d'auteur)

A narrow epidemiologic survey was conducted during a four-month period of intense malaria transmission in Dielmo, a holoendemic Senegalese village. Longitudinal clinical and parasitologic follow-up indicate that clinical malaria episodes always occurred after an abrupt increase in parasite densities. Polymerase chain reaction analysis of #Plasmodium falciparum$ parasites was carried out in blood samples collected longitudinally from 10 children who had experienced, several clinical episodes during this period. Our data show that the genetic diversity of the parasites circulating in this village is very large. The successive clinical episodes experienced by each child were caused by genetically distinct parasite populations that were recently inoculated and multiplied in an apparently unrestricted manner. Importantly, the genetic characteristics of the parasite populations detected during phases of asymptomatic carriage differed from those causing a clinical episode, suggesting that the various factors that control of parasite growth in these children are strain-specific. (Résumé d'auteur)

The Dielmo project, initiated in 1990, consisted of long-term investigations on host-parasite relationships and the mechanisms of protective immunity in the 247 residents of a Senegalese village in which malaria is holoendemic. Anopheles gambiae s.l. and An. funestus constituted more than 98% of 11,685 anophelines collected and were present all year round. Inoculation rates of Plasmodium falciparum, P. malariae, and P. ovale averaged respectively 0.51, 0.10, and 0.04 infective bites per person per night. During a four-month period of intensive parasitologic and clinical monitoring, Plasmodium falciparum, P. malariae, and P. ovale were observed in 72.0%, 21.1% and 6.0%, respectively, of the 8,539 thick smears examined. Individual longitudinal data revealed that 98.6% of the villagers harbored trophozoites of P. falciparum at least once during the period of the study. Infections by P. malariae and P. ovale were both observed in individuals of all age groups and their cumulative prevalences reached 50.5% and 40.3%, respectively. Malaria was responsible for 162 (60.9%) of 266 febrile episodes; 159 of these attacks were due to P. falciparum, three to P. ovale, and none to P. malariae. The incidence of malaria attacks was 40 times higher in children 0–4 years of age than in adults more than 40 years old. Our findings suggest that sterile immunity and clinical protection are never fully achieved in humans continuously exposed since birth to intense transmission.

Background Mass treatment with ivermectin is a proven strategy for controlling onchocerciasis as a public health problem, but it is not known if it can also interrupt transmission and eliminate the parasite in endemic foci in Africa where vectors are highly efficient. A longitudinal study was undertaken in three hyperendemic foci in Mali and Senegal with 15 to 17 years of annual or six-monthly ivermectin treatment in order to assess residual levels of infection and transmission and test whether ivermectin treatment could be safely stopped in the study areas. Methodology/Principal Findings Skin snip surveys were undertaken in 126 villages, and 17,801 people were examined. The prevalence of microfilaridermia was, Author Summary The control of onchocerciasis, or river blindness, is based on annual or six-monthly ivermectin treatment of populations at risk. This has been effective in controlling the disease as a public health problem, but it is not known whether it can also eliminate infection and transmission to the extent that treatment can be safely stopped. Many doubt that this is feasible in Africa. A study was undertaken in three hyperendemic onchocerciasis foci in Mali and Senegal where treatment has been given for 15 to 17 years. The results showed that only few infections remained in the human population and that transmission levels were everywhere below postulated thresholds for elimination. Treatment was subsequently stopped in test areas in each focus, and follow-up evaluations did not detect any recrudescence of infection or transmission. Hence, the study has provided the first evidence that onchocerciasis elimination is feasible with ivermectin treatment in some endemic foci in Africa. Although further studies are needed to determine to what extent these findings can be extrapolated to other areas in Africa, the principle of onchocerciasis elimination with ivermectin treatment has been established.

L'auteur rapporte trois cas de resistance apparus en octobre et novembre 1988 in vivo et in vitro, dans une banlieue de Dakar. Quatre annees seulement separe l'apparition du premier cas de resistance in vitro du premier cas in vivo, remettant en cause l'absence de prophylaxie des visiteurs

Background Anopheles funestus is one of the major malaria vectors in tropical Africa, notably in Senegal. The highly anthropophilic and endophilic behaviours of this mosquito make it a good target for vector control operations through the use of insecticide treated nets, long-lasting insecticide nets and indoor residual spraying. However, little is known about patterns of resistance to insecticides and the underlying resistance mechanisms in field populations of this vector in Senegal. Methods Here, we assessed the susceptibility status of An. funestus populations from Gankette Balla, located in northern Senegal and investigated the potential resistance mechanisms. Results WHO bioassays indicated that An. funestus is resistant to lambda-cyhalothrin 0.05 % (74.64 % mortality), DDT 4 % (83.36 % mortality) and deltamethrin 0.05 % (88.53 % mortality). Suspected resistance was observed to permethrin 0.75 % (91.19 % mortality), bendiocarb 0.1 % (94.13 % mortality) and dieldrin 4 % (96.41 % mortality). However, this population is fully susceptible to malathion 5 % (100 % mortality) and fenitrothion 1 % (100 % mortality). The microarray and qRT-PCR analysis indicated that the lambda-cyhalothrin resistance in Gankette Balla is conferred by metabolic resistance mechanisms under the probable control of cytochrome P450 genes among which CYP6M7 is the most overexpressed. The absence of overexpression of the P450 gene, CYP6P9a, indicates that the resistance mechanism in Senegal is different to that observed in southern Africa. Conclusions This study represents the first report of pyrethroid and DDT resistance in An. funestus from Senegal and shows that resistance to insecticides is not only confined to An. gambiae as previously thought. Therefore, urgent action should be taken to manage the resistance in this species to ensure the continued effectiveness of malaria control. Electronic supplementary material The online version of this article (doi:10.1186/s13071-016-1735-7) contains supplementary material, which is available to authorized users.

Background Malaria vector control in Africa relies on insecticides targeting adult mosquito vectors via insecticide treated nets or indoor residual spraying. Despite the proven efficacy of these strategies, the emergence and rapid rise in insecticide resistance in malaria vectors raises many concerns about their sustainability. Therefore, the monitoring of insecticide resistance is essential for resistance management strategies implementation. We investigated the kdr mutation frequencies in 20 sympatric sites of An. arabiensis Patton, An. coluzzii Coetzee & Wilkerson and An. gambiae Giles and its importance in malaria vector control by evaluating the susceptibility to insecticides in four representative sites in Senegal. Methods Sibling species identification and kdr mutation detection were determined using polymerase chain reaction on mosquitoes collected using pyrethrum sprays collection in 20 sites belonging to two transects with differential insecticide selection pressure. The World Health Organization (WHO) tube test was used to determine phenotypic resistance of An. gambiae s.l. to DDT, deltamethrin, lambdacyholothrin, permethrin, bendiocarb and malathion in four representative sites. Results The L1014F kdr mutation was widely distributed and was predominant in An. gambiae in comparison to An. arabiensis and An. coluzzii. The bioassay tests showed a general trend with a resistance to DDT and pyrethroids and a susceptibility to organophosphate and carbamate according to WHO thresholds. For deltamethrin and permethrin, the two most used insecticides, no significant difference were observed either between the two transects or between mortality rates suggesting no differential selection pressures on malaria vectors. The study of the KD times showed similar trends as comparable levels of resistance were observed, the effect being more pronounced for permethrin. Conclusions Our study showed a widespread resistance of malaria vectors to DDT and pyrethroids and a widespread distribution of the 1014F kdr allele. These combined observations could suggest the involvement of the kdr mutation. The existence of other resistance mechanisms could not be ruled out as a proportion of mosquitoes did not harbour the kdr allele whereas the populations were fully resistant. The susceptibility to carbamate and organophosphate could be exploited as alternative for insecticide resistance management.

Background During the last decades two dams were constructed along the Senegal River. These intensified the practice of agriculture along the river valley basin. We conducted a study to assess malaria vector diversity, dynamics and malaria transmission in the area. Methods A cross-sectional entomological study was performed in September 2008 in 20 villages of the middle Senegal River valley to evaluate the variations of Anopheles density according to local environment. A longitudinal study was performed, from October 2008 to January 2010, in 5 selected villages, to study seasonal variations of malaria transmission. Results Among malaria vectors, 72.34% of specimens collected were An. arabiensis, 5.28% An. gambiae of the S molecular form, 3.26% M form, 12.90% An. pharoensis, 4.70% An. ziemanni, 1.48% An. funestus and 0.04% An. wellcomei. Anopheles density varied according to village location. It ranged from 0 to 21.4 Anopheles/room/day and was significantly correlated with the distance to the nearest ditch water but not to the river. Seasonal variations of Anopheles density and variety were observed with higher human biting rates during the rainy season (8.28 and 7.55 Anopheles bite/man/night in October 2008 and 2009 respectively). Transmission was low and limited to the rainy season (0.05 and 0.06 infected bite/man/night in October 2008 and 2009 respectively). During the rainy season, the endophagous rate was lower, the anthropophagic rate higher and L1014F kdr frequency higher. Conclusions Malaria vectors are present at low-moderate density in the middle Senegal River basin with An. arabiensis as the predominant species. Other potential vectors are An. gambiae M and S form and An. funestus. Nonetheless, malaria transmission was extremely low and seasonal.

International audience; Background: African horse sickness (AHS) is an equine disease endemic to Senegal. The African horse sickness virus (AHSV) is transmitted to the mammalian hosts by midges of the Culicoides Latreille genus. During the last epizootic outbreak of AHS in Senegal in 2007, 1,169 horses died from this disease entailing an estimated cost of 1.4 million euros. In spite of the serious animal health and economic implications of AHS, very little is known about determinants involved in transmission such as contact between horses and the Culicoides species suspected of being its vectors. Methods: The monthly variation in host/vector contact was determined in the Niayes area, Senegal, an area which was severely affected by the 2007 outbreak of AHS. A horse-baited trap and two suction light traps (OVI type) were set up at each of five sites for three consecutive nights every month for one year. Results: Of 254,338 Culicoides midges collected 209,543 (82.4%) were female and 44,795 (17.6%) male. Nineteen of the 41 species collected were new distribution records for Senegal. This increased the number of described Culicoides species found in Senegal to 53. Only 19 species, of the 41 species found in light trap, were collected in the horse-baited trap (23,669 specimens) largely dominated by Culicoides oxystoma (22,300 specimens, i.e. 94.2%) followed by Culicoides imicola (482 specimens, i.e. 2.0%) and Culicoides kingi (446 specimens, i.e. 1.9%). Conclusions: Culicoides oxystoma should be considered as a potential vector of AHSV in the Niayes area of Senegal due to its abundance on horses and its role in the transmission of other Culicoides-borne viruses.