Distribution of the members of Anopheles gambiae and pyrethroid knock-down resistance gene (kdr) in Guinea-Bissau, West Africa

Une étude entomologique a été réalisée en 2002 dans quatre localités couvrant différents faciès écologiques de la Guinée Bissau : Buba Tombao (forêt), Gabu (savane), Cacheu (mangrove) et Bissau (urbain) afin i) d'étudier la distribution des membres du complexe Anopheles gambiae (Diptera: Culicidae) ii) d'évaluer le statut de résistance de ces vecteurs du paludisme aux insecticides (perméthrine 0.75%, DDT 4%) et enfin iii) de rechercher la présence et la distribution de la mutation kdr au sein de ces populations. Les femelles de moustiques adultes issues de captures matinales à l'intérieur des maisons ont été testées suivant les procédures OMS (kit de bio essai et papier imprégné) afin d'évaluer leur statut de résistance aux insecticides. Les spécimens testés ont été identifiés et caractérisés pour la présence de la mutation kdr par PCR. En Guinée Bissau, dans les localités étudiées, le complexe An. gambiae est dominé par An. gambiae s.s. (avec les deux formes moléculaires S et M représentées) vivant en sympatrie sur le littoral avec une faible proportion d'An. melas. Les populations d'An. gambiae s.s. exposées aux deux insecticides se sont révélées sensibles quelle que soit leur provenance. La mutation kdr Leu-Phe a été détectée en de très faibles fréquences seulement dans deux localités situées respectivement en zone urbaine (Bissau) et en savane (Gabu). Cette mutation est présente uniquement dans la forme moléculaire S à Gabu (avec une fréquence allélique de 0.14) et dans les deux formes moléculaires M et S à Bissau avec des fréquences alléliques respectives de 0.06 et de 0.02. Ces résultats suggèrent que les populations d'An. gambiae s.s., vecteur le plus fréquent du paludisme en Guinée Bissau, demeurent encore sensibles aux pyréthrinoides et au DDT 4%. Ce statut de sensibilité ainsi que la fréquence des gènes de résistance tel que le kdr doivent être surveillés dans le futur particulièrement dans les zones urbaine et de savane soumises à une utilisation intensive d'insecticides. (Résumé d'auteur

Dynamics of multiple insecticide resistance in the malaria vector Anopheles gambiae in a rice growing area in South-Western Burkina Faso

<p>Abstract</p> <p>Background</p> <p>Insecticide resistance of the main malaria vector, <it>Anopheles gambiae</it>, has been reported in south-western Burkina Faso, West Africa. Cross-resistance to DDT and pyrethroids was conferred by alterations at site of action in the sodium channel, the Leu-Phe <it>kdr </it>mutation; resistance to organophosphates and carbamates resulted from a single point mutation in the oxyanion hole of the acetylcholinesterase enzyme designed as <it>ace-1</it>^<it>R</it>.</p> <p>Methods</p> <p>An entomological survey was carried out during the rainy season of 2005 at Vallée du Kou, a rice growing area in south-western Burkina Faso. At the Vallée du Kou, both insecticide resistance mechanisms have been previously described in the M and S molecular forms of <it>An. gambiae</it>. This survey aimed i) to update the temporal dynamics and the circumsporozoite infection rate of the two molecular forms M and S of <it>An. gambiae </it>ii) to update the frequency of the Leu-Phe <it>kdr </it>mutation within these forms and finally iii) to investigate the occurrence of the <it>ace-1</it>^{<it>R </it>}mutation.</p> <p>Mosquitoes collected by indoor residual collection and by human landing catches were counted and morphologically identified. Species and molecular forms of <it>An. gambiae</it>, <it>ace-1</it>^{<it>R </it>}and Leu-Phe <it>kdr </it>mutations were determined using PCR techniques. The presence of the circumsporozoite protein of <it>Plasmodium falciparum </it>was determined using ELISA.</p> <p>Results</p> <p><it>Anopheles gambiae </it>populations were dominated by the M form. However the S form occurred in relative important proportion towards the end of the rainy season with a maximum peak in October at 51%. Sporozoite rates were similar in both forms. The frequency of the Leu-Phe <it>kdr </it>mutation in the S form reached a fixation level while it is still spreading in the M form. Furthermore, the <it>ace</it>-<it>1</it>^{<it>R </it>}mutation prevailed predominately in the S form and has just started spreading in the M form. The two mutations occurred concomitantly both in M and S populations.</p> <p>Conclusion</p> <p>These results showed that the Vallée du Kou, a rice growing area formerly occupied mainly by M susceptible populations, is progressively colonized by S resistant populations living in sympatry with the former. As a result, the distribution pattern of insecticide resistance mutations shows the occurrence of both resistance mechanisms concomitantly in the same populations. The impact of multiple resistance mechanisms in M and S populations of <it>An. gambiae </it>on vector control measures against malaria transmission, such as insecticide-treated nets (ITNs) and indoor residual spraying (IRS), in this area is discussed.</p

Distribution and frequency of kdr mutations within Anopheles gambiae s.l. populations and first report of the ace.1 G119S mutation in Anopheles arabiensis from Burkina Faso (West Africa).

Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tAn entomological survey was carried out at 15 sites dispersed throughout the three eco-climatic regions of Burkina Faso (West Africa) in order to assess the current distribution and frequency of mutations that confer resistance to insecticides in An. gambiae s.l. populations in the country. Both knockdown (kdr) resistance mutation variants (L1014F and L1014S), that confer resistance to pyrethroid insecticides, were identified concomitant with the ace-1 G119S mutation confirming the presence of multiple resistance mechanisms in the An. gambiae complex in Burkina Faso. Compared to the last survey, the frequency of the L1014F kdr mutation appears to have remained largely stable and relatively high in all species. In contrast, the distribution and frequency of the L1014S mutation has increased significantly in An. gambiae s.l. across much of the country. Furthermore we report, for the first time, the identification of the ace.1 G119S mutation in An. arabiensis populations collected at 8 sites [corrected]. This mutation, which confers resistance to organophosphate and carbamate insecticides, has been reported previously only in the An. gambiae S and M molecular forms. This finding is significant as organophosphates and carbamates are used in indoor residual sprays (IRS) to control malaria vectors as complementary strategies to the use of pyrethroid impregnated bednets. The occurrence of the three target-site resistance mutations in both An. gambiae molecular forms and now An. arabiensis has significant implications for the control of malaria vector populations in Burkina Faso and for resistance management strategies based on the rotation of insecticides with different modes of action.National Malaria Control Program (NMCP) of Burkina Fas

Comparison of swarming, mating performance and longevity of males Anopheles coluzzii between individuals fed with different natural fruit juices in laboratory and semi-field conditions.

BACKGROUND: It is assumed that malaria vectors feed on locally available nectar sources to obtain energy. Sugar feeding is energetically critical for the Anopheles male swarming and mating activities. However, little is known about the impact of local nectar feeding on male physiological development and its consequences on male mosquito life traits in the malaria control context. This study aimed to evaluate the influence of local fruit juices on the life traits of males Anopheles coluzzii. METHODS: Swarming characteristics (number of males in swarm, number of mating pairs, and swarm duration) in semi-field conditions; mating rate and longevity in a laboratory setting were compared between males An. coluzzii fed exclusively with mango, papaya or banana juices. The trophic preference was investigated in semi-field conditions. RESULTS: The results of this study showed that in the laboratory, mosquitoes fed with papaya juices lived on average longer (10 days) than those fed with banana or mango juices (5 days) and had higher a mating rate (53%) than those fed with banana juice (40%). In the semi-field, the swarm size of mosquitoes fed with banana juice (85 males) was larger than that of mosquitoes fed with mango juice (60 males). The number of mating pairs formed from banana-fed male swarms (17 mating pairs) was higher than that formed from mango-fed male swarm (8 mating pairs). There was no difference in swarming duration between male treatments. Male mosquitoes had a preference for papaya and banana juices. CONCLUSIONS: The results indicate that the origin of plant-derived feeding is an important factor in the survival and reproduction of mosquitoes. This calls for further investigations of chemical contents of nectars and their impact on the physiological development of mosquitoes

Campylobacter Spp. Epidemiology and Antimicrobial Susceptibility in a Developing Country, Burkina Faso (West Africa)

Data on campylobacteriosis are almost nonexistent in Burkina Faso. In this study conducted from 2006 to 2008 in Ouagadougou, stool specimens and sociodemographic data were collected from 1 246 patients attending the university teaching hospital for enteritis. Stool samples were analyzed for the presence of Campylobacter by the direct culture method on selective mCCDA agar followed by antibiotic susceptibility testing on the isolated strains. The isolation rate of Campylobacter was 2.3%,comprising of the following species C. jejuni (51.8%), C. coli (13.8%), and C. upsaliensis (3.5%). However, 30.9% of the isolates were unidentified. No resistant strain was found to gentamicin. The resistance to amoxicillin+clavulanic acid (3.4%) was lower than those (10.3-34.5%) to the other antibiotics: erythromycin (10.3%), tetracycline (10.3%), ciprofloxacin (13.8%), amoxicillin (24.1%) and ceftriaxone (34.5%), nalidixic acid (34.5%). Significant associations were found between Campylobacter enteritis and contact with animals (P=0.03), and HIV infection (P&lt;0.0001), in contrast to other sociodemographic and seasonal factors. From the data obtained Amoxicillin+clavulanic acid appear to be the first choice for treatment. The implementation of a national program may be helpful in controlling the spread of the disease and the increase of resistance to antibiotics.Keywords: Campylobacter, epidemiology, HIV, drug resistance, Burkina Fas

Assessment of the ecologically dependent post-zygotic isolation between Anopheles coluzzii and Anopheles gambiae.

Within the Anopheles gambiae complex, the sibling species An. coluzzii and An. gambiae are undergoing sympatric speciation. These species are characterized by rare hybrids in most of their geographical distribution. A strong assortative mating mediated by spatial swarm segregation has been shown whereas no intrinsic post-zygotic barriers have been found in laboratory conditions. To test the role of the hybridisation in reproductive isolation in natural populations transplant experiment are therefore needed to establish the significance of post-zygotic barriers. Previous studies indicated that predation is one of the major forces driving ecological divergence between An. gambiae and An. coluzzii. Here we extended these studies to their hybrids. Parental species and their F1 hybrids from reciprocal crosses were generated by the forced-mating technique as follows: female An. coluzzii × male An. coluzzii; female An. coluzzii × male An. gambiae; female An. gambiae × male An. coluzzii and female An. gambiae × Male An. gambiae. First instar larvae of each group from the crossing (here after An. coluzzii, Hybrid COL/GAM, Hybrid GAM/COL and An. gambiae, respectively) were transplanted in a field experiment with predation effect. Emergence success, development time of larvae and body size of the newly emerging adults were estimated as fitness components and then compared between parental species and F1 hybrids in absence and in presence of predators. Our findings confirm that An. coluzzii had higher fitness than An. gambiae in presence of predators versus in absence of predators. Moreover, the fitness of the F1 hybrid COL/GAM whose female parent was An. coluzzii matched that of An. coluzzii while that of the F1 reciprocal hybrid GAM/COL was similar to An. gambiae

Population dynamics of Anopheles gambiae s.l. in Bobo-Dioulasso city: bionomics, infection rate and susceptibility to insecticides.

Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tBACKGROUND: Historical studies have indicated that An. gambiae s.s. is the predominant malaria vector species in Bobo-Dioulasso the second biggest city of Burkina Faso (West Africa). However, over the last decade, An. arabiensis appears to be replacing An. gambiae s.s. as the most prevalent malaria vector in this urban setting. To investigate this species transition in more detail the present study aims to provide an update on the malaria vector composition in Bobo-Dioulasso, and also the Plasmodium infection rates and susceptibility to insecticides of the local An. gambiae s.l. population. METHODS: An entomological survey was carried out from May to December 2008 in Dioulassoba and Kodeni (central and peripheral districts respectively), which are representative of the main ecological features of the city. Sampling consisted of the collection of larval stages from water bodies, and adults by monthly indoor residual spraying (IRS) using aerosol insecticides. Insecticide susceptibility tests were performed using the WHO filter paper protocol on adults emerged from larvae. PCR was used to determine vector species and to identify resistance mechanisms (kdr and ace-1(R)). The Plasmodium infection rate was estimated by ELISA performed on female mosquitoes collected indoors by IRS. RESULTS: An. arabiensis was found to be the major malaria vector in Bobo-Dioulasso, comprising 50 to 100% of the vector population. The sporozoite infection rate for An. arabiensis was higher than An. gambiae s.s. at both Dioulassoba and Kodeni. An. gambiae s.l. was resistant to DDT and cross-resistant to pyrethroids at the two sites with higher levels of resistance observed in An. gambiae s.s. than An. arabiensis. Resistance to 0.1% bendiocarb was observed in the An. gambiae s.s. S form but not the M form or in An. arabiensis. The L1014F kdr mutation was detected in the two molecular forms of An. gambiae s.s. at varying frequencies (0.45 to 0.92), but was not detected in An. arabiensis, suggesting that other mechanisms are involved in DDT resistance in this species. The ace-1(R) mutation was only detected in the S molecular form and was observed at the two sites at similar frequency (0.3). CONCLUSIONS: Over the last ten years, An. arabiensis has become the major malaria vector in Bobo-Dioulasso city where it was formerly present only at low frequency. However, the ecological determinant that enhances the settlement of this species into urban and peri-urban areas of Bobo-Dioulasso remains to be clarified. The impact of the changing An. gambiae s.l. population in this region for vector control including resistance management strategies is discussed.CORUS 6015MIM 60098

Paratransgenesis to control malaria vectors: a semi-field pilot study

BACKGROUND: Malaria still remains a serious health burden in developing countries, causing more than 1 million deaths annually. Given the lack of an effective vaccine against its major etiological agent, Plasmodium falciparum, and the growing resistance of this parasite to the currently available drugs repertoire and of Anopheles mosquitoes to insecticides, the development of innovative control measures is an imperative to reduce malaria transmission. Paratransgenesis, the modification of symbiotic organisms to deliver anti-pathogen effector molecules, represents a novel strategy against Plasmodium development in mosquito vectors, showing the potential to reduce parasite development. However, the field application of laboratory-based evidence of paratransgenesis imposes the use of more realistic confined semi-field environments. METHODS: Large cages were used to evaluate the ability of bacteria of the genus Asaia expressing green fluorescent protein (Asaia (gfp)), to diffuse in Anopheles stephensi and Anopheles gambiae target mosquito populations. Asaia (gfp) was introduced in large cages through the release of paratransgenic males or by sugar feeding stations. Recombinant bacteria transmission was directly detected by fluorescent microscopy, and further assessed by molecular analysis. RESULTS: Here we show the first known trial in semi-field condition on paratransgenic anophelines. Modified bacteria were able to spread at high rate in different populations of An. stephensi and An. gambiae, dominant malaria vectors, exploring horizontal ways and successfully colonising mosquito midguts. Moreover, in An. gambiae, vertical and trans-stadial diffusion mechanisms were demonstrated. CONCLUSIONS: Our results demonstrate the considerable ability of modified Asaia to colonise different populations of malaria vectors, including pecies where its association is not primary, in large environments. The data support the potential to employ transgenic Asaia as a tool for malaria control, disclosing promising perspective for its field application with suitable effector molecules

Trends in Insecticide Resistance in Natural Populations of Malaria Vectors in Burkina Faso, West Africa: 10 Years’ Surveys

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