Search

Background: Cutaneous leishmaniasis (CL) is an endemic neglected tropical disease prevalent in several areas where seasonal malaria transmission is active. We assessed the effect of indoor residual spraying (IRS) and the mass distribution of long-lasting insecticide-treated bednets (LLINs) for malaria control on sand fly population diversity and abundance, and its impact on the risk of Leishmania transmission in the district of Baroueli, endemic for CL in Mali., Methods: Kemena and Sougoula, two villages in the district of Baroueli, were selected for entomology surveys from March to September 2016 to evaluate sand fly species composition and density, and Leishmania infection rates in the vector Phlebotomus duboscqi. The surveys followed an annual indoor residual spraying and mass distribution of long-lasting insecticide-treated bednets (IRS/LLINs) that began in 2011 for malaria vector control. We also carried out a leishmanin skin test (LST) survey in the two villages to determine the incidence of Leishmania infection in humans living in the endemic area., Results: A total of 2936 sand fly specimens, 1013 males and 1923 females, were collected and identified from the two villages throughout the study period. Fourteen species, 2 belonging to the genus Phlebotomus and 12 to the genus Sergentomyia, were documented. The genus Sergentomyia constituted 91% of collected sand flies versus 9% for the genus Phlebotomus (P. duboscqi and P. rodhaini). Of those, P. duboscqi was the most abundant, representing 99.6% of the collected Phlebotomus species. In both villages, P. duboscqi was most abundant during the end of dry season (June). The prevalence of Leishmania infection in individual females of P. duboscqi by PCR was 3.5%. After 5 years of the IRS/LLINs, the incidence of Leishmania infection in the human population as measured by LST was 4.2%., Conclusions: Compared to historical data collected from 2005-2008, a considerable reduction was observed in both sand fly density and prevalence of human Leishmania infection in the villages of Kemena and Sougoula, Baroueli District, following IRS/LLINs. This suggests that IRS/LLINs used for mosquito control also impacts sand fly vectors reducing the incidence of leishmaniasis., Trial Registration: NCT00344084 . Registered: 23 June 2006.

Background: Malaria epidemiology in Mauritania has been characterized on the basis of epidemiological strata, defined by climatic and geographic features, which divide the country into three zones: Sahelian zone, Sahelo-Saharan transition zone, and Saharan zone. The association between geographic stratification and malaria transmission was assessed through a series of parasitological and entomological surveys., Methods: Surveys were conducted during the 'cool' dry season in 2011, 'hot' dry season in 2012, and rainy season in 2013 in a total of 12 sentinel sites. Finger-prick capillary blood samples were collected from children aged 2-9 years old in randomly selected households for microscopic examination and rapid diagnostic test for malaria. Adult mosquitoes were sampled by pyrethrum spray catch and CDC light traps and identified using morphological keys and molecular tools., Results: Of 3445 children included, 143 (4.15 %) were infected with malaria parasites including Plasmodium falciparum (n = 71, 2.06 %), Plasmodium vivax (57, 1.65 %), P. falciparum-P. vivax (2, 0.06 %), Plasmodium ovale (12, 0.35 %), and Plasmodium malariae (1, 0.03 %). A large majority of P. falciparum infections were observed in the Sahelo-Saharan zone. Malaria prevalence (P < 0.01) and parasite density (P < 0.001) were higher during the rainy season (2013), compared to cool dry season (2011). Plasmodium vivax was mainly observed in the Saharan region [43 of 59 (73 %) P. vivax infections], mostly in Nouakchott districts, with no significant seasonal variation. Of 3577 mosquitoes captured, 1014 (28.3 %) belonged to Anopheles spp. Anopheles gambiae was the predominant species in all three epidemiological strata during the 'cool' dry season in 2011 but was absent in all study sites, except for Teyarett district in Nouakchott, during the 'hot' dry season in 2012. During the rainy season in 2013, An. gambiae, Anopheles arabiensis, Anopheles pharoensis, and Anopheles rufipes were abundant in different zones., Conclusions: The results of the present study support the stratification of malaria in Mauritania. However, the Sahelian zone had the lowest malaria prevalence, while the Sahelo-Saharan zone had the highest malaria burden. Local changes due to anthropogenic factors (i.e., human migration, urbanization, malaria interventions) should be considered in order to optimize the control strategy.

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: Anopheles gambiae s.s. and An. coluzzii are two of the most important malaria vector species in sub-Saharan Africa. These recently-diverged sibling species do not exhibit intrinsic post-zygotic barriers to reproduction and are thought to be separated by strong assortative mating combined with selection against hybrids. At present, little is known about the ecological conditions that determine hybridization and introgression between these cryptic taxa., Methods: Swarm segregation and assortative mating were studied in Western Burkina Faso in the villages of Vallée du Kou (VK7) and Soumousso which differed in terms of which sibling species was much rarer than the other, and in Bana where both occurred in similar proportions. Swarms and pairs in copula were collected and genotyped, the proportion of intra and interspecific mating determined, and interspecific sperm transfer checked genetically. Females were collected through larval and adult indoor collections and genotyped or sexed-and-genotyped via a novel multiplex PCR., Results: A total of 3,687 males and 220 females were collected and genotyped from 109 swarms. Only 3 swarms were composed of males from both species, and these were from the village of VK7 where An. gambiae s.s. was comparatively rare. Mixed-species pairs captured in copula were only detected in that area and made for 3.62 % and 100 % of mating pairs involving An. coluzzii and An. gambiae s.s. individuals, respectively. The high An. gambiae s.s. cross-mating rate was mirrored by high rates of hybridizations estimated from female larvae and adults indoor collections. This contrasted with Soumousso, where despite being much less common than An. gambiae s.s., An. coluzzii males did not form mixed swarms, females were not found in interspecific swarms or copula and hybridization rates were low in both sibling species., Conclusions: These data suggest that ecological conditions leading to rare An. gambiae s.s. in populations dominated by An. coluzzii may promote a breakdown of spatial swarm segregation and assortative mating between the two species. The lower overall hybridization rates observed at the larval and adult indoor stages compared to cross-mating rates support the idea that post-mating selection processes acting against hybrids may occur mostly prior to and/or at the early larval stages.

Background: Zika virus (ZIKV; genus Flavivirus, family Flaviviridae) is an emerging virus of medical importance maintained in a zoonotic cycle between arboreal Aedes spp. mosquitoes and nonhuman primates in African and Asian forests. Serological evidence and virus isolations have demonstrated widespread distribution of the virus in Senegal. Several mosquito species have been found naturally infected by ZIKV but little is known about their vector competence., Methods: We assessed the vector competence of Ae. aegypti from Kedougou and Dakar, Ae. unilineatus, Ae. vittatus and Ae. luteocephalus from Kedougou in Senegal for 6 ZIKV strains using experimental oral infection. Fully engorged female mosquitoes were maintained in an environmental chamber set at 27 ± 1 °C and 80 ± 5% Relative humidity. At day 5, 10 and 15 days post infection (dpi), individual mosquito saliva, legs/wings and bodies were tested for the presence of ZIKV genome using real time RT-PCR to estimate the infection, dissemination, and transmission rates., Results: All the species tested were infected by all viral strains but only Ae. vittatus and Ae. luteocephalus were potentially capable of transmitting ZIKV after 15 dpi with 20 and 50% of mosquitoes, respectively, delivering epidemic (HD 78788) and prototype (MR 766) ZIKV strains in saliva., Conclusion: All the species tested here were susceptible to oral infection of ZIKV but only a low proportion of Ae. vittatus and Ae. luteocephalus had the viral genome in their saliva and thus the potential to transmit the virus. Further investigations are needed on the vector competence of other species associated with ZIKV for better understanding of the ecology and epidemiology of this virus in Senegal.

African horse sickness- and bluetongue virus are orbiviruses transmitted by Culicoides biting midges (Diptera: Ceratopogonidae) to horses and to ruminants, respectively. Since the last epizootic outbreak of African horse sickness in 2007 in Senegal, extensive investigations have been undertaken to improve our knowledge on Culicoides species involved locally in the transmission of the virus. The purpose of this study was to compare and quantify the host preferences of potential vectors of these orbiviruses on horse and sheep and to study their circadian rhythm. We found that Culicoides oxystoma and species of the sub-genus Avaritia (Culicoides imicola, Culicoides bolitinos and Culicoides pseudopallidipennis) had a preference for horse when compared to sheep (the predicted ratio between horse and sheep was 80 for C. oxystoma and 26 for C. imicola), and were mostly crepuscular: C. oxystoma had continuous activity throughout the diel with peaks in numbers collected after sunrise and sunset, while C. imicola was mostly nocturnal with peak after sunset. Unexpectedly, species of the subgenus Lasiohelea was also collected during this study. This diurnal biting species was a nuisance pest for both animal species used as bait., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Culicoides biting midges (Diptera: Ceratopogonidae) are important vectors of arboviruses in Africa. Culicoides oxystoma has been recently recorded in the Niayes region of Senegal (West Africa) and its high abundance on horses suggests a potential implication in the transmission of the African horse sickness virus in this region. This species is also suspected to transmit bluetongue virus to imported breeds of sheep. Little information is available on the biology and ecology of Culicoides in Africa. Therefore, understanding the circadian host-seeking activity of this putative vector is of primary importance to assess the risk of the transmission of Culicoides-borne pathogens. To achieve this objective, midges were collected using a sheep-baited trap over two consecutive 24-h periods during four seasons in 2012. A total of 441 Culicoides, belonging to nine species including 418 (94.8%) specimens of C. oxystoma, were collected. C. oxystoma presented a bimodal circadian host-seeking activity at sunrise and sunset in July and was active 3 h after sunrise in April. Daily activity appeared mainly related to time periods. Morning activity increased with the increasing temperature up to about 27 °C and then decreased with the decreasing humidity, suggesting thermal limits for C. oxystoma activity. Evening activity increased with the increasing humidity and the decreasing temperature, comprised between 20 and 27 °C according to seasons. Interestingly, males were more abundant in our sampling sessions, with similar activity periods than females, suggesting potential animal host implication in the facilitation of reproduction. Finally, the low number of C. oxystoma collected render practical vector-control recommendations difficult to provide and highlight the lack of knowledge on the bio-ecology of this species of veterinary interest.

Aedes aegypti L. (Diptera: Culicidae) is a major vector of yellow fever, dengue, and chikungunya viruses throughout tropical and subtropical areas of the world. Although the southernmost part of Mauritania along the Senegal river has long been recognized at risk of yellow fever transmission, Aedes spp. mosquitoes had never been reported northwards in Mauritania. Here, we report the first observation of Aedes aegypti aegypti (L.) and Aedes (Ochlerotatus) caspius (Pallas, 1771) in the capital city, Nouakchott. We describe the development sites in which larvae of the two species were found, drawing attention to the risk for emergence of arbovirus transmission in the city., (© The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

A growing number of recent reports have implicated Rickettsia felis as a human pathogen, paralleling the increasing detection of R. felis in arthropod hosts across the globe, primarily in fleas. Here Anopheles gambiae mosquitoes, the primary malarial vectors in sub-Saharan Africa, were fed with either blood meal infected with R. felis or infected cellular media administered in membrane feeding systems. In addition, a group of mosquitoes was fed on R. felis-infected BALB/c mice. The acquisition and persistence of R. felis in mosquitoes was demonstrated by quantitative PCR detection of the bacteria up to day 15 postinfection. R. felis was detected in mosquito feces up to day 14. Furthermore, R. felis was visualized by immunofluorescence in salivary glands, in and around the gut, and in the ovaries, although no vertical transmission was observed. R. felis was also found in the cotton used for sucrose feeding after the mosquitoes were fed infected blood. Natural bites from R. felis-infected An. gambiae were able to cause transient rickettsemias in mice, indicating that this mosquito species has the potential to be a vector of R. felis infection. This is particularly important given the recent report of high prevalence of R. felis infection in patients with "fever of unknown origin" in malaria-endemic areas.

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.

Sylvatic arboviruses have been isolated in Senegal over the last 50 years. The ecological drivers of the pattern and frequency of virus infection in these species are largely unknown. We used time series analysis and Bayesian hierarchical count modeling on a long-term arbovirus dataset to test associations between mosquito abundance, weather variables, and the frequency of isolation of dengue, yellow fever, chikungunya, and Zika viruses. We found little correlation between mosquito abundance and viral isolations. Rainfall was a negative predictor of dengue virus (DENV) isolation but a positive predictor of Zika virus isolation. Temperature was a positive predictor of yellow fever virus (YFV) isolations but a negative predictor of DENV isolations. We found slight interference between viruses, with DENV negatively associated with concurrent YFV isolation and YFV negatively associated with concurrent isolation of chikungunya virus. These findings begin to characterize some of the ecological associations of sylvatic arboviruses with each other and climate and mosquito abundance., (© The American Society of Tropical Medicine and Hygiene.)

Background: The influence of environmental and climatic factors on malaria vector bionomics and transmission is an important topic in the context of climatic change particularly at macro-geographical level. Sahelian areas could be particularly affected due to heterogeneous features including high inter-annual variability in rainfall and others associated parameters. Therefore, baseline information on the impact of environmental and climatic factors on malaria transmission at micro-geographical level is required for vector risk management and implementation of control strategies., Methods: Malaria vectors were collected indoors by pyrethrum spray catches in 14 villages belonging to 4 different landscape classes (wooded savanna, shrubby savanna, bare soils and steppe) in the sylvo-pastoral area of Senegal. Plasmodium falciparum infection rates were determined using an indirect enzyme-linked immunosorbent assay (ELISA)., Results: An. arabiensis was the predominant species in all landscape classes and was the only species collected at the end of the rainy season excepted in villages located in bare soils where it cohabited with An. coluzzii. Mean temperature and relative humidity showed similar variations in all the landscape classes covered whereas rainfall was more heterogeneous in terms of pattern, frequency and amount. The mean densities of An. arabiensis displayed high seasonal differences with peaks observed in August or September. A positive non-significant correlation was observed between An. arabiensis densities for rainfall and humidity whereas a negative non-significant correlation was reported for temperature. Plasmodium falciparum-infected mosquitoes were detected only in wooded savanna and bare soils villages., Conclusions: These observations suggest key roles played by landscape classes and rainfall in malaria vector densities, infection rates and malaria transmission that could be more pronounced in villages situated in wooded savanna and bare soils. Due to the close relationship between environmental and meteorological parameters in this Sahelian region, additional studies on the impact of these parameters are required to further ascertain their association with entomological parameters involved in malaria transmission. From the public health point of view, such information could be useful for human population settlements as well as for monitoring and modelling purposes giving early warning system for implementation of interventions in these unstable transmission zones.

Objective: To investigate the potential for domestic and wild populations of Aedes aegypti from Dakar and Kedougou to develop a disseminated infection after exposure to DENV-3 and DENV-1., Methods: We have exposed sylvatic and urban population of Ae. aegypti from Senegal to bloomeals containing dengue serotype 1 and 3. At different incubation period, individual mosquito legs/wings and bodies were tested for virus presence using real time RT-PCR to estimate the infection and dissemination rates., Results: The data indicated low susceptibility to DENV-3 (infection: 2.4-15.2%, and dissemination rates: 0-8.3%) and higher susceptibility to DENV-1 (infection and dissemination rates up to 50%)., Conclusion: Aedes aegypti from Senegal seem able to develop a disseminated infection of DENV-1 and DENV-3. Further studies are needed to test their ability to transmit the two serotypes., (© 2014 John Wiley & Sons Ltd.)

Background: Zika virus (ZIKV; genus Flavivirus, family Flaviviridae) is maintained in a zoonotic cycle between arboreal Aedes spp. mosquitoes and nonhuman primates in African and Asian forests. Spillover into humans has been documented in both regions and the virus is currently responsible for a large outbreak in French Polynesia. ZIKV amplifications are frequent in southeastern Senegal but little is known about their seasonal and spatial dynamics. The aim of this paper is to describe the spatio-temporal patterns of the 2011 ZIKV amplification in southeastern Senegal., Methodology/findings: Mosquitoes were collected monthly from April to December 2011 except during July. Each evening from 18:00 to 21:00 hrs landing collections were performed by teams of 3 persons working simultaneously in forest (canopy and ground), savannah, agriculture, village (indoor and outdoor) and barren land cover sites. Mosquitoes were tested for virus infection by virus isolation and RT-PCR. ZIKV was detected in 31 of the 1,700 mosquito pools (11,247 mosquitoes) tested: Ae. furcifer (5), Ae. luteocephalus (5), Ae. africanus (5), Ae. vittatus (3), Ae. taylori, Ae. dalzieli, Ae. hirsutus and Ae. metallicus (2 each) and Ae. aegypti, Ae. unilinaetus, Ma. uniformis, Cx. perfuscus and An. coustani (1 pool each) collected in June (3), September (10), October (11), November (6) and December (1). ZIKV was detected from mosquitoes collected in all land cover classes except indoor locations within villages. The virus was detected in only one of the ten villages investigated., Conclusions/significance: This ZIKV amplification was widespread in the Kédougou area, involved several mosquito species as probable vectors, and encompassed all investigated land cover classes except indoor locations within villages. Aedes furcifer males and Aedes vittatus were found infected within a village, thus these species are probably involved in the transmission of Zika virus to humans in this environment.

To assess the risk of emergence of chikungunya virus (CHIKV) in West Africa, vector competence of wild-type, urban, and non-urban Aedes aegypti and Ae. vittatus from Senegal and Cape Verde for CHIKV was investigated. Mosquitoes were fed orally with CHIKV isolates from mosquitoes (ArD30237), bats (CS13-288), and humans (HD180738). After 5, 10, and 15 days of incubation following an infectious blood meal, presence of CHIKV RNA was determined in bodies, legs/wings, and saliva using real-time reverse transcription-polymerase chain reaction. Aedes vittatus showed high susceptibility (50-100%) and early dissemination and transmission of all CHIKV strains tested. Aedes aegypti exhibited infection rates ranging from 0% to 50%. Aedes aegypti from Cape Verde and Kedougou, but not those from Dakar, showed the potential to transmit CHIKV in saliva. Analysis of biology and competence showed relatively high infective survival rates for Ae. vittatus and Ae. aegypti from Cape Verde, suggesting their efficient vector capacity in West Africa., (© The American Society of Tropical Medicine and Hygiene.)

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.

During the wet season of 2010, yellow fever virus (YFV) was detected in field-collected mosquitoes in the Kédougou region in southeastern Senegal. During this outbreak, we studied the association of the abundance of YFV-infected mosquitoes and land cover features to try and understand the dynamics of YFV transmission within the region. In total, 41,234 mosquito females were collected and tested for virus infection in 5,152 pools. YFV was detected in 67 pools; species including Aedes furcifer (52.2% of the infected pools), Ae. luteocephalus (31.3% of the infected pools), Ae. taylori (6.0% of the infected pools) and six other species (10.4% of the infected pools) captured in September (13.4%), October (70.1%), and November (16.4%). Spatially, YFV was detected from mosquitoes collected in all land cover classes but mainly, forest canopies (49.2%). Human infection is likely mediated by Ae. furcifer, the only species found infected with YFV within villages. Villages containing YFV-infected mosquitoes were significantly closer to large forests (> 2 ha) than villages in which no infected mosquitoes were detected., (© The American Society of Tropical Medicine and Hygiene.)

West Nile virus (WN virus) is one of the most widespread arbovirus and exhibits a great genetic diversity with 8 lineages, at least 4 (1, 2, Koutango, and putative new) are present in Africa. In West Africa, Culex neavei and Culex quinquefasciatus are considered as potential vectors for WN virus transmission in sylvatic or urban context. We analyzed the vector competence of these Culex species from Senegal for African lineages and envelope proteins sequences of viral strains used. We showed that lineage 1 is transmitted by both Culex mosquitoes, whereas the putative new lineage 8 is transmitted only by Cx. neavei. Our findings suggest that genetic variability can affect vector competence and depend on mosquito. However, when considering the infective life rate, the mosquito population seems to be inefficient for WN virus transmission in the field and could explain the low impact of WN virus in Africa.

After a period of heavy rainfall, an outbreak of Rift Valley fever occurred in southern Mauritania during September-November 2012. A total of 41 human cases were confirmed, including 13 deaths, and 12 Rift Valley fever virus strains were isolated. Moudjeria and Temchecket Departments were the most affected areas.

A Rift Valley fever (RVF) outbreak in humans and animals occurred in Mauritania in 2010. Thirty cases of RVF in humans and 3 deaths were identified. RVFV isolates were recovered from humans, camels, sheep, goats, and Culex antennatus mosquitoes. Phylogenetic analysis of isolates indicated a virus origin from western Africa.

Usutu virus (USUV), a flavivirus belonging to the Japanese encephalitis serocomplex, was isolated for the first time from a Culex neavei mosquito in 1959 in South Africa. Despite multiple isolations of USUV from Cx. neavei in Africa, its vector competence remains unproven. Therefore, we infected Cx. neavei orally with the USUV reference strain and used reverse transcription-polymerase chain reaction and an indirect immunofluorescence assay to detect virus in bodies, legs, wings, and saliva of mosquitoes. We demonstrated the susceptibility of Cx. neavei mosquitoes for the USUV reference strain, its potential to be transmitted, and infection, dissemination, and transmission rates of 90.9%, 40.0%, and 81.3%, respectively. Also, we showed that infection rates are dependent on the virus titer of the blood meal. Given the bionomics of Cx. neavei, its role as enzootic vector for USUV in Africa in a mosquito-bird transmission cycle or as bridge vector for USUV transmission to humans is discussed.

Vector competence of Aedes aegypti populations from six locations in different bioclimatic zones and habitats of Senegal was assessed for sylvatic (ArD 140875) and epidemic (ArA 6894) dengue 2 virus (DENV-2) isolates. F1 generation mosquitoes were fed with a blood meal containing 10(6.5) and 1.6 x 10(7) tissue culture infectious dose (TCID50) of the sylvatic DENV-2 isolate or 10(6.5) TCID50 of the epidemic isolate and incubated for 14 days. After this period, legs and wings of each individual were pooled and the corresponding body was collected separately. An immunofluorescence assay was used to test bodies and wings/legs for DENV-2 infection separately. The results showed that: (i) Senegalese Ae. aegypti populations have lower vector competence (infection rate 0-26%, dissemination rate 10-100%) for sylvatic and epidemic dengue viruses than populations from Asia and America; (ii) there was no obvious geographic variation in susceptibility among mosquito populations; (iii) the only apparent factor affecting the susceptibility was the virus titre; and (iv) except for that of Kédougou, all populations were able to disseminate the virus. Overall our findings, while extended to four other populations, confirm previous studies showing low susceptibility of Senegalese Ae. aegypti populations.

An entomological survey conducted in 2002 in Guinea Bissau aimed i) to study the distribution of the members of Anopheles gambiae Giles complex (Diptera: Culicidae) throughout four ecological areas extended from mangrove to savannah ii) to evaluate the insecticide susceptibility status of these malaria vectors exposed to permethrin 0.75% and DDT4%, and finally iii) to investigate the occurrence and the spread of the Leu-Phe knock down resistance (kdr) gene associated with pyrethroid and DDT resistance within these vector populations. Adult female mosquitoes issued from indoor morning collections were tested using WHO procedures, test kits and impregnated papers to assess their insecticide susceptibility status. Tested specimens were identified by PCR assays and characterized for the kdr gene. Malaria vectors were mainly dominated elsewhere by An. gambiae s.s. (both S and M molecular forms) living in sympatry with low proportion of An. melas in the littoral. An. gambiae s.s. tested populations were fully susceptible both to permethrin 0.75% and to DDT 4% irrespective to their location and ecotypes. The Leu-Phe kdr mutation was detected at low frequency only in two sites respectively urban (Bissau) and Guinea-savannah (Gabu) areas. It occurred only in the S molecular form in Gabu (at the frequency of 0.14) and both in the S and M molecular forms in Bissau at the frequency of 0.06 and 0.02 respectively. These results suggested that the populations of An. gambiae s.s., the most frequent malaria vector in Guinea Bissau, still remain cross-susceptible to pyrethroids and DDT This susceptibility status and the frequency of resistance mechanism such as the kdr mutation must be monitored in the future particularly in the urban and savannah areas with continuous and intensive use of insecticides.

From January to April 2005, an epidemic of chikungunya virus (CHIKV) illness occurred in the Union of Comoros. Entomological studies were undertaken during the peak of the outbreak, from March 11 to March 31, aimed at identifying the primary vector(s) involved in transmission so that appropriate public health measures could be implemented. Adult mosquitoes were collected by backpack aspiration and human landing collection in homes and neighborhoods of clinically ill patients. Water-holding containers were inspected for presence of mosquito larvae. Adult mosquitoes were analyzed by RT-PCR and cultivation in cells for the presence of CHIK virus and/or nucleic acid. A total of 2,326 mosquitoes were collected and processed in 199 pools. The collection consisted of 62.8% Aedes aegypti, 25.5% Culex species, and 10.7% Aedes simpsoni complex, Eretmapodites spp and Anopheles spp. Seven mosquito pools were found to be positive for CHIKV RNA and 1 isolate was obtained. The single CHIKV mosquito isolate was from a pool of Aedes aegypti and the minimum infection rate (MIR) for this species was 4.0, suggesting that Ae. aegypti was the principal vector responsible for the outbreak. This was supported by high container (31.1%), household (68%), and Breteau (126) indices, with discarded tires (58.8%) and small cooking and water storage vessels (31.1%) registering the highest container indices.

In October 2003, 9 human cases of hemorrhagic fever were reported in 3 provinces of Mauritania, West Africa. Test results showed acute Rift Valley fever virus (RVFV) infection, and a field investigation found recent circulation of RVFV with a prevalence rate of 25.5% (25/98) and 4 deaths among the 25 laboratory-confirmed case-patients. Immunoglobulin M against RVFV was found in 46% (25/54) of domestic animals. RVFV was also isolated from the mosquito species Culex poicilipes. Genetic comparison of virion segments indicated little variation among the strains isolated. However, phylogenetic studies clearly demonstrated that these strains belonged to the East-Central African lineage for all segments. To our knowledge, this is the first time viruses of this lineage have been observed in an outbreak in West Africa. Whether these strains were introduced or are endemic in West Africa remains to be determined.

From June 1995 to January 1998, entomological studies carried out in five villages located in the Delta's Saloum have allowed to better understand the contribution of An. melas Theobald (1903) to malaria transmission in mangrove swamp. Among the five villages studied, three of them (Simal, Djilor and Marlothie) located along the Saloum river, are colonised by An. arabiensis; the two others (Djifere and Diakhanor) located between the sea and the river, are colonised by An. melas. During the rainy season and at the beginning of the dry season, An. melas and An. arabiensis are sympatric. The ratio of An. melas/An. arabiensis increases when we go closer the coast where An. melas becomes quite exclusive. When An. melas is predominant, endophagy, endophily and anthropophily are very marked. The parturity rates are lower in An. melas than in An. arabiensis. In the predominance area of each species, transmission is on the same level. During the period of sympatry, An. arabiensis is responsible for the transmission and when it is absent, An. melas carries on. Transmission occurs from July to March with a maximum at the beginning of the dry season. In the villages of the mangrove swamp, its prolongation until the middle of the dry season is due to An. melas.

We previously investigated malaria in the southern health district of the city of Dakar, which includes the oldest neighborhoods. In this study, we investigated malaria in the central health district, corresponding to the central area of the conurbation. The study was carried out at 12 sites, from March 1996 to February 1997. The sites were selected such that the entire district was covered and included 2 sites in the shanty town and three in an old village that has been absorbed into the city. We carried out prospective monthly entomological analyses with a view to identifying the vectors and the mode of transmission of malaria. We also carried out clinical and parasitological follow up to determine the incidence of parasitemia and of bouts of malaria. Insects were collected overnight from humans and the insects remaining the next morning in 10 bedrooms in the health district were collected. For clinical and parasitological follow up, families were visited at home once per week and their clinical state was assessed. Blood smears were taken to facilitate the detection of bouts of malaria. Body temperature was measured and we checked for the presence of organisms in the blood systematically during the last weekly visit of each month. For a total of 308 collections at night from human volunteers and 1,395 bedroom collections of residual fauna, we obtained 12,879 Culicidae females, 199 (1.5%) of which were anopheles mosquitoes, with Culex quinquefasciatus accounting for 98% of the remaining mosquitoes. As in the southern district, A. arabiensis was the only species of the A. gambiae complex collected. Anopheles mosquitoes accounted for only 0.3 bites per man per night and 0.07 females per room. They were therefore poorly represented in this district and were not detected at all at five sites. They were found in large numbers only during the rainy season, especially in September, when they accounted for 2.25 bites per man per night and 0.3 females per room at 3 sites in an undeveloped zone in which 81.4% of all the anopheles mosquitoes were collected. The parturition frequency of the biting females was 32.6% and that of the females collected in houses was 50.0%. None of the A. arabiensis females dissected (98.5% of those collected) carried Plasmodium sporozoites. The clinical and parasitological follow up concerned 2,583 individuals, aged from 1 month to 80 years, from 285 families resident in Dakar who volunteered for the study; 41.9% of these individuals were less than 15 years old and 92.2% had been living in Dakar for more than 2 years. Thick and thin blood smears taken monthly showed the frequency of the parasite to be 1.0% and that of gametocytes to be 0.1%. P. falciparum was the only parasite detected in the subjects. Plasmodium infections were observed in all age groups, with a frequency of 0.4% (adults over the age of 20 years) to 1.6% (children under two years of age). Parasitized subjects were detected in every month of the study, with a frequency of 0.4% (in January) to 1.9% (in December). The largest number of cases detected in a three-month period (38.8% of all cases) was that for October to December, the three-month period immediately after the rainy season (July to September). Parasite frequency, which was no higher than 1. 2% at 10 sites, was clearly higher at two sites in the shanty town (3.8 and 6.8%), mostly inhabited by immigrants from rural areas. At the end of the study year, satisfactory weekly follow up was considered to have been achieved for 1,067 of the participants. The annual incidence of parasitemia in this cohort was 5.1% and that of malaria was 2.4%. Incidence did not vary significantly with age and was between 1.8% and 7.6% for parasitemia and between 0.8% and 3.5% for malaria. However, significant differences in incidence were observed between areas. Incidence was higher at the two sites in the shanty town, with rates of 12.1% and 36.5% for parasitemia and 6.1% and 15.9% for malaria. (ABSTRACT TR

Since 1969, 63 cases of airport malaria have been reported in Western Europe, 24 of which occurred in France. Most were due to Plasmodium falciparum. In 1994, 7 cases occurred in and around Roissy Charles de Gaulle airport (CDG), showing 4 types of contamination: among employees working on airstrips or opening containers, among residents living near the airport, among people living at some distance from the airport after a secondary transport of vectors, and by vectors transported in luggage. In-flight or stop-over infection is not considered as airport malaria. The infective anophelines originated from airports where malaria transmission occurs, mostly in subsaharan Africa. A tentative list is given taking into account aerial traffic with France. Surveys in the airports of Dakar (Senegal), Cotonou (Benin), Abidjan (Cote d'Ivoire) and Yaoundé (Cameroun) found potential vectors in all of these from July to September. After 1994, the Contrôle Sanitaire aux Frontières (CSF) in charge at CDG concentrated its efforts on the flights at risk, as well as information and sensitization of airline companies, which resulted in 73% and 87% of the flights at risk being properly disinsected in 1995 and 1996. Despite pyrethroid resistance in Anopheles gambiae s.s. in West Africa, the efficacy of aircraft spraying with permethrin aerosols is still acceptable. However, surveillance of resistance should be improved and search for nonpyrethroid insecticides suitable for aircraft strongly encouraged.

A supervision of the focus of human cutaneous leishmaniasis of Keur Moussa has been carried out in 1988-1989 and in 1991-1992. Among the 13 species gathering the 10,144 phlebotomine sandflies trapped, two belong to genus Phlebotomus, the others to genus Sergentomyia. Phlebotomus duboscqi, that has been found out by Deded et al. in 1980 as the vector of this leishmaniasis in Senegal, is the most represented species after Sergentomyia schwetzi, with respectively 32.3 and 28.5% of the found during these two periods. It is twice more abundant and frequent in the monastery area than the religious one. This difference may be due to the better micro-climatic conditions, the abundance of rodents and the human proximity. After the rainy seasons that influence a lot P. duboscqi's activity, the density of phlebotomine sandflies makes a progressive rise, as well as the temperature and humidity, to reach two maxima in April-May and July-August. Parasitological studies on females of phlebotomine sandflies and rodents Arvicanthis niloticus, Mastomys erythroleucus and Cricetomys gambianus are negative. This focus seems to be again in an inter-epidemic phase.

To complete a parasitological survey, entomological prospections were carried out in the southern sanitary District of Dakar, the most urbanized of the city and which includes the city centre and the oldest administrative districts. The prospections took place between June 1994 and May 1995 in sites 1.5 km apart, and distributed in such a manner that they covered the entire area. On a monthly basis, female Culicidae were collected in each site at night on human volunteers, followed the next day by the collection of early morning residual fauna in 10 bedrooms located in district concessions. For a total of 308 collections at night on human volunteers and from 1,510 rooms for the residual fauna, 22,901 female Culicidae were caught of which 167 anopheles, corresponding to 0.7%, the remaining 98.5% being Culex quinquefasciatus. This was the species that thus explained the mosquito-nuisance of which the inhabitants of the southern District complained during the period of survey. The female anopheles collected belonged to 2 species, An. arabiensis for 97.6% of those caught and An. pharoensis for 2.4%. An. arabiensis were very slightly represented in the southern District with a density of aggressive females of 0.26 bite/man/night (B/M/N) and a density per room of 0.05 female. The aggressive populations appeared to be relatively important only at the end of the rainy season (September-October) with an average of 0.65 B/M/N in sites located at the periphery of the district with a maximum of 1.33 B/M/N. The highest density of endophilic females registered at the end of the rainy season was 0.1 and its highest value in a given site was 0.36 female/room. The parturity rate of aggressive females was 43.5% and those collected in houses of 84% with an anthropophilic index of 0.98. None of the dissected An. arabiensis females (77.3% of those collected) was a carrier of Plasmodium sporozoites and the circum-sporozoite antigen was not found. A very weak density of An. arabiensis and absence of plasmodial infection among dissected females favoured the absence of malarial transmission in the southern District for the period considered. However malaria transmission could not be absolutely ruled out given the presence of hematozoa carriers, as was revealed by the longitudinal follow-up of a cohort carried out concurrently with the entomological prospections of whom some were residents having declared permanent residence in the city for over two years. This entomological data explain the results of the afore mentioned parasitological survey which, with a registered plasmodic index of 0.3%, means that the southern District can be considered as non endemic. The area is however exposed to the risk of epidemic malaria following an important proliferation of anopheles, which is always possible after heavy rains and flooding and/or an important immigration of persons coming from regions of high malarial endemicity.

From September 1992 to October 1993 a longitudinal entomological study was carried out in two villages located in different ecological conditions of Senegal, a sahelian area and a sudan-type savanna. Mosquitoes were sampled by night-bites catches and by daytime pyrethrum spray collections. In both villages Anopheles gambiae s.l. is the main vector with An. gambiae in the savanna area of Wassadou and An. arabiensis in the sahelian area of Thiaye. Malaria transmission is mainly seasonal with a man biting rate (ma) and an entomological inoculation rate (h) higher in Wassadou than in Thiaye. In this last one (sahelian area), a high variation of An. gambiae s.l. density was observed, females disappear in the dry season. In the rainy season the main biting rate increases but no infected bite was recorded. In Wassadou (sudan-type savanna), a great difference in An. gambiae s.l. specific composition was observed with An. gambiae predominant in the rainy season and An. arabiensis generally more abundant in the dry season. The biting and inoculation rates were minimum during the dry season (ma = 4 bites/man/night; h = 0.07 infected bites/man/night-, they increase during the rainy season (ma: 52 bites/man/night; h = 1.6 infected bites/man/night). An inhabitant of this village gets annually some 63, bites and 220 infected bites of An. gambiae s.l., mainly during the six months of the rainy season and the early dry season.

Some informations about malaria transmission, which has until nox difficult to get, can be obtained thanks to the use of molecular biology tools, PCR mainly. In Senegal, we use that technique to solve two kinds of problems: -Identification of species of the Anopheles gambiae complex: PCR technique is useful compared to other diagnostic methods (chromosome pattern, DNA probes, etc.) because it enables quickly and simply identification of captured anopheles from the DNA contained in their legs. The rest of the mosquito is tested by circumsporozoite protein antigen ELISA and blood meal ELISA. The data obtained are used to determine distribution, cycles, trophic preferences and comparative vectorial capacities of Anopheles gambiae, Anopheles arabiensis and Anopheles melas. -Identification in a mosquito blood meal of the individual bitten: we propose to evaluate factors (weight, age, sex, location of bedroom, etc.) which could explain why individuals are more, or less, bitten by a Plasmodium vector. Genetic typing is used on inhabitants'leukocytes DNA and on the leukocyte DNA extracted from the blood meal of resting anopheles. Through the high degree of polymorphism of three (AAAG)n microsatellites markers, we hope, using PCR, to attribute each blood meal to one individual. Statistical analysis will be used to identify attractivity factors and to determine more precisely the inoculation rates for each group rather than the classical rate calculated with male adults volunteers.

From April 1990 to March 1992 a longitudinal entomological study was carried out in Dielmo village, Senegal, an area of Sudan-type savanna. Mosquitoes were sampled by night-bite collections and pyretnrum spray collections. Seven anopheles species were identified: An. gambiae s.s. An. arabiensis, An. funestus, An. pharoensis, An. rufipes, An. squamosus and An. ziemanni. Present throughout the year, An. gambiae s.l. and An. funestus represented more than 98% of anopheles captured on man. A yearly wave of An. gambiae s.l. was observed in the rainy season and An. funestus was generally more abundant in the dry season. The sporozoite rate was 1.5% and 1.3%, respectively, for these two species. Sporozoite typing by monoclonal antibodies indicated that the proportion of infected salivary glands was 92.7% P. falciparum, 18.2% P malariae and 8.2% P. ovale. The inoculation rate was calculated to be respectively 111, 21 and 8 infective bites per human for P. falciparum, P. malariae and P. ovale during the first year. Transmission was highest in the second year, with respectively 272, 54 and 25 infective bites per human.

During 23 months period, entomological surveys were carried out in three villages of a mangrove area and two others far of the mangrove in the south part of Senegal. An. gambiae s.s was the main malaria vector and the sampling of its population was done by human baits catch. The An. gambiae density was important in the rainy season and the malaria transmission occurred from July to November; the inoculation rate rose from 0 to 123 infected bites per man. Marked yearly and local variations of the transmission intensity were observed. The transmission intensity was higher in the villages far of the mangrove than in those near. The variations of the transmission intensity were related to the larval breeding sites and to the longevity of the An. gambiae females.