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Comparative susceptibility to Plasmodium falciparum of the molecular forms M and S of Anopheles gambiae and Anopheles arabiensis
Mamadou O Ndiath, Anna Cohuet, Ablaye Gaye, Lassana Konate, Catherine Mazenot, Ousmane Faye, Christian Boudin, Cheikh Sokhna, Jean-Fran?ois Trape
Malaria Journal , 2011, DOI: 10.1186/1475-2875-10-269
Abstract: 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.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).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.Plasmodium falciparum, the deadliest agent of human malaria, is exclusively transmitted by Anopheles mosquitoes. In Africa, species belonging to the Anopheles gambiae complex are responsible for a large proportion of malaria cases. This complex is composed of species morphologically identical but distinct in their distribution, ecology and contribution in malaria transmission. While Anopheles merus, Anopheles melas, Anopheles bwambae and Anopheles quadriannulatus have sporadic or null role in malaria transmission due to restricted geographical distribution and/or zoophily, Anopheles gambiae s.s. and Anopheles arabiensis are the most important in terms of epidemiology [1,2]. Anopheles gambiae s.s. itself was shown to be subdivided in incipient species, namely M and S molecular forms [3], both vectors of
Dynamics of transmission of Plasmodium falciparum by Anopheles arabiensis and the molecular forms M and S of Anopheles gambiae in Dielmo, Senegal
Mamadou Ndiath, Cécile Brengues, Lassana Konate, Cheikh Sokhna, Christian Boudin, Jean Trape, Didier Fontenille
Malaria Journal , 2008, DOI: 10.1186/1475-2875-7-136
Abstract: The aim of this study was to compare the epidemiologic role of Anopheles arabiens is and the molecular forms M and S of Anopheles gambiae in the transmission of Plasmodium in a rural areas of southern Senegal, Dielmo. The sampling of mosquitoes was carried out monthly between July and December 2004, during the rainy season, by human volunteers and pyrethrum spray catches.Anopheles arabiensis, An. gambiae M and S forms coexisted during the rainy season with a predominance of the M form in September and the peak of density being observed in August for the S form. Similar parity rates were observed in An. arabiensis [70.9%] (n = 86), An. gambiae M form [68.7%] (n = 64) and An. gambiae S form [81.1%] (n = 156). The circumsporozoite protein (CSP) rates were 2.82% (n = 177), 3.17% (n = 315) and 3.45% (n = 405), with the mean anthropophilic rates being 71.4% (n = 14), 86.3% (n = 22) and 91.6% (n = 24) respectively for An. arabiensis and An. gambiae M and S forms. No significant difference was observed either in host preference or in Plasmodium falciparum infection rates between sympatric M and S populations.No difference was observed either in host preference or in Plasmodium falciparum infection rates between sympatric M and S populations, but they present different dynamics of population. These variations are probably attributable to different breeding conditions.The Anopheles gambiae complex consists of at least seven species among which Anopheles gambiae s.s. is one of the most anthropophilic malaria vectors in Africa [1]. The adaptation of An. gambiae to humans and its environment involves an ongoing speciation process that can be best demonstrated by the existence of a number of incipient taxonomic units, characterized by the presence of paracentric inversions leading to different chromosomal arrangements [2]. This speciation process is primarily observed in West Africa, where five chromosomal forms of An. gambiae s.s. have been described and designated with a non-Li
The Anopheles gambiae Odorant Binding Protein 1 (AgamOBP1) Mediates Indole Recognition in the Antennae of Female Mosquitoes  [PDF]
Harald Biessmann,Evi Andronopoulou,Max R. Biessmann,Vassilis Douris,Spiros D. Dimitratos,Elias Eliopoulos,Patrick M. Guerin,Kostas Iatrou,Robin W. Justice,Thomas Kr?ber,Osvaldo Marinotti,Panagiota Tsitoura,Daniel F. Woods,Marika F. Walter
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0009471
Abstract: Haematophagous insects are frequently carriers of parasitic diseases, including malaria. The mosquito Anopheles gambiae is the major vector of malaria in sub-Saharan Africa and is thus responsible for thousands of deaths daily. Although the role of olfaction in A. gambiae host detection has been demonstrated, little is known about the combinations of ligands and odorant binding proteins (OBPs) that can produce specific odor-related responses in vivo. We identified a ligand, indole, for an A. gambiae odorant binding protein, AgamOBP1, modeled the interaction in silico and confirmed the interaction using biochemical assays. RNAi-mediated gene silencing coupled with electrophysiological analyses confirmed that AgamOBP1 binds indole in A. gambiae and that the antennal receptor cells do not respond to indole in the absence of AgamOBP1. This case represents the first documented instance of a specific A. gambiae OBP–ligand pairing combination, demonstrates the significance of OBPs in odor recognition, and can be expanded to the identification of other ligands for OBPs of Anopheles and other medically important insects.
Species composition of the Anopheles gambiae complex across eco-vegetational zones in Bayelsa State, Niger Delta region, Nigeria  [PDF]
A. Ebenezer , S.N. Okiwelu , P.I. Agi , M.A.E Noutcha , T.S. Awolola & A.O. Oduola
Journal of Vector Borne Diseases , 2012,
Abstract: Background & objectives: Correct vector identification is an important task in the planning and implementationof malaria vector control programmes. This study was designed to provide baseline information on the speciescomposition and distribution of members of the Anopheles gambiae complex in three eco-vegetational zones inBayelsa state, Nigeria.Methods: Adult mosquitoes were collected by pyrethrum spray catch (PSC) in randomly selected houses duringSeptember 2009–August 2010. Anopheles mosquitoes were identified using standard morphological keys.Mosquitoes identified as An. gambiae s.l. were used for species specific PCR-assays.Results: Out of 203 Anopheles gambiae s.l. successfully amplified, 180 (88.7%) were Anopheles gambiae s.s.,14 (6.9%) were An. melas and 9 (4.4%) were An. arabiensis. The variation in the sibling species composition ofAn. gambiae s.l. was not significant (p >0.05). Anopheles gambiae s.s. was predominant in all the collectionswith three sibling species occurring in all the eco-vegetational zones.Interpretation & conclusion: The observation of An. melas in the fresh water swamp forest of Yenagoa is ofimportance in malaria epidemiology. These findings are of importance in the planning and implementation ofmalaria vector control strategy in the three eco-vegetational zones of Bayelsa state.
Multimodal Pyrethroid Resistance in Malaria Vectors, Anopheles gambiae s.s., Anopheles arabiensis, and Anopheles funestus s.s. in Western Kenya  [PDF]
Hitoshi Kawada, Gabriel O. Dida, Kazunori Ohashi, Osamu Komagata, Shinji Kasai, Takashi Tomita, George Sonye, Yoshihide Maekawa, Cassian Mwatele, Sammy M. Njenga, Charles Mwandawiro, Noboru Minakawa, Masahiro Takagi
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0022574
Abstract: Anopheles gambiae s.s., Anopheles arabiensis, and Anopheles funestus s.s. are the most important species for malaria transmission. Pyrethroid resistance of these vector mosquitoes is one of the main obstacles against effective vector control. The objective of the present study was to monitor the pyrethroid susceptibility in the 3 major malaria vectors in a highly malaria endemic area in western Kenya and to elucidate the mechanisms of pyrethroid resistance in these species. Gembe East and West, Mbita Division, and 4 main western islands in the Suba district of the Nyanza province in western Kenya were used as the study area. Larval and adult collection and bioassay were conducted, as well as the detection of point mutation in the voltage-gated sodium channel (1014L) by using direct DNA sequencing. A high level of pyrethroid resistance caused by the high frequency of point mutations (L1014S) was detected in An. gambiae s.s. In contrast, P450-related pyrethroid resistance seemed to be widespread in both An. arabiensis and An. funestus s.s. Not a single L1014S mutation was detected in these 2 species. A lack of cross-resistance between DDT and permethrin was also found in An. arabiensis and An. funestus s.s., while An. gambiae s.s. was resistant to both insecticides. It is noteworthy that the above species in the same area are found to be resistant to pyrethroids by their unique resistance mechanisms. Furthermore, it is interesting that 2 different resistance mechanisms have developed in the 2 sibling species in the same area individually. The cross resistance between permethrin and DDT in An. gambiae s.s. may be attributed to the high frequency of kdr mutation, which might be selected by the frequent exposure to ITNs. Similarly, the metabolic pyrethroid resistance in An. arabiensis and An. funestus s.s. is thought to develop without strong selection by DDT.
Additional Selection for Insecticide Resistance in Urban Malaria Vectors: DDT Resistance in Anopheles arabiensis from Bobo-Dioulasso, Burkina Faso  [PDF]
Christopher M. Jones, Hyacinthe K. Toé, Antoine Sanou, Moussa Namountougou, Angela Hughes, Abdoulaye Diabaté, Roch Dabiré, Frederic Simard, Hilary Ranson
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0045995
Abstract: In the city of Bobo-Dioulasso in Burkina Faso, Anopheles arabiensis has superseded Anopheles gambiae s.s. as the major malaria vector and the larvae are found in highly polluted habitats normally considered unsuitable for Anopheles mosquitoes. Here we show that An. gambiae s.l. adults emerging from a highly polluted site in the city centre (Dioulassoba) have a high prevalence of DDT resistance (percentage mortality after exposure to diagnostic dose = 65.8% in the dry season and 70.4% in the rainy season, respectively). An investigation into the mechanisms responsible found an unexpectedly high frequency of the 1014S kdr mutation (allele frequency = 0.4), which is found at very low frequencies in An. arabiensis in the surrounding rural areas, and an increase in transcript levels of several detoxification genes, notably from the glutathione transferase and cytochrome P450 gene families. A number of ABC transporter genes were also expressed at elevated levels in the DDT resistant An. arabiensis. Unplanned urbanisation provides numerous breeding grounds for mosquitoes. The finding that Anopheles mosquitoes adapted to these urban breeding sites have a high prevalence of insecticide resistance has important implications for our understanding of the selective forces responsible for the rapid spread of insecticide resistant populations of malaria vectors in Africa.
Influence of biological and physicochemical characteristics of larval habitats on the body size of Anopheles gambiae mosquitoes (Diptera: Culicidae) along the Kenyan coast  [PDF]
Joseph M. Mwangangi, Charles M. Mbogo, Ephantus J. Muturi, Joseph G. Nzovu, Ephantus W. Kabiru, John I. Githure, Robert J. Novak , John C. Beier
Journal of Vector Borne Diseases , 2007,
Abstract: Background & objectives: The number and productivity of larval habitats ultimately determine thedensity of adult mosquitoes. The biological and physicochemical conditions at the larval habitataffect larval development hence affecting the adult body size. The influence of biological and physicochemicalcharacteristics on the body size of Anopheles gambiae was assessed in Jaribuni village,Kilifi district along the Kenyan Coast.Methods: Ten cages measuring 1 × 1 × 1 m (1 m3) with a netting material were placed in 10 differentaquatic habitats, which were positive for anopheline mosquito larvae. Emergent mosquitoes werecollected daily by aspiration and the wing lengths were determined by microscopy. In the habitats,physicochemical parameters were assessed: pH, surface debris, algae and emergent plants, turbidity,substrate, nitrate, ammonia, phosphate and chlorophyll a content.Results: A total of 685 anopheline and culicine mosquitoes were collected from the emergent cages.Only female mosquitoes were considered in this study. Among the Anopheles spp, 202 were An.gambiae s.s., eight An. arabiensis, two An. funestus, whereas the Culex spp was composed of 214Cx. quinquefasciatus, 10 Cx. tigripes, eight Cx. annulioris and one Cx. cumminsii. The mean winglength of the female An. gambiae s.s. mosquitoes was 3.02 mm (n = 157), while that of An. arabiensiswas 3.09 mm (n = 9). There were no associations between the wing lengths and the environmentaland chemical parameters, except for a positive correlation between wing length of An. gambiae andchlorophyll a content (r = 0.622). The day on which the mosquitoes emerged was not significant forthe anopheline (p = 0.324) or culicine mosquitoes (p = 0.374), because the mosquito emerged fromthe cages on a daily basis.Interpretation & conclusion: In conclusion, there was variability in production of emergent mosquitoesfrom different habitats, which means that there should be targeted control on these habitatsbased on productivity.
Status of insecticide susceptibility in Anopheles gambiae s.l. from malaria surveillance sites in The Gambia
Martha Betson, Musa Jawara, Taiwo Awolola
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-187
Abstract: Anopheles larvae were collected from six malaria surveillance sites (Brikama, Essau, Farafenni, Mansakonko, Kuntaur and Basse) established by the National Malaria Control Programme and the UK Medical Research Council Laboratories in The Gambia. The mosquitoes were reared to adulthood and identified using morphological keys and a species-specific polymerase chain reaction assay. Two- to three-day old adult female mosquitoes were tested for susceptibility to permethrin, deltamethrin and DDT using standard WHO protocols, insecticide susceptibility test kits and treated papers.All Anopheles mosquitoes tested belonged to the Anopheles gambiae complex. Anopheles arabiensis was predominant (54.1%), followed by An. gambiae s.s. (26.1%) and Anopheles melas (19.8%). Anopheles gambiae s.s. and An. arabiensis were found at all six sites. Anopheles melas was recorded only at Brikama. Mosquitoes from two of the six sites (Brikama and Basse) were fully susceptible to all three insecticides tested. However, DDT resistance was found in An. gambiae from Essau where the 24 hours post-exposure mortality was <80% but 88% for permethrin and 92% for deltamethrin.This current survey of insecticide resistance in Anopheles provides baseline information for monitoring resistance in The Gambia and highlights the need for routine resistance surveillance as an integral part of the proposed nation wide IRS intervention using DDT.Malaria vector control, using either insecticide-treated nets (ITNs) or indoor residual spraying (IRS), relies on the continued susceptibility of Anopheles mosquitoes to a limited number of insecticides. Twelve insecticides from four classes (organochlorines, organophosphates, carbamates and pyrethroids) have been recommended for IRS [1,2], but only pyrethroids have been approved for treating bed nets. Since the mid-1950s, there have been numerous reports of reduced Anopheles susceptibility to DDT, malathion, fenithrotion, propoxur and bendiocarb, and resistance to all fo
Dynamics of insecticide resistance in malaria vectors in Benin: first evidence of the presence of L1014S kdr mutation in Anopheles gambiae from West Africa
Innocent Djègbè, Olayidé Boussari, Aboubakar Sidick, Thibaud Martin, Hilary Ranson, Fabrice Chandre, Martin Akogbéto, Vincent Corbel
Malaria Journal , 2011, DOI: 10.1186/1475-2875-10-261
Abstract: Anopheles gambiae s.l populations were collected from October 2008 to June 2010 in four sites selected on the basis of different use of insecticides and environment. WHO susceptibility tests were carried out to detect resistance to DDT, fenitrothion, bendiocarb, permethrin and deltamethrin. The synergist piperonyl butoxide was used to assess the role of non-target site mechanisms in pyrethroid resistance. Anopheles gambiae mosquitoes were identified to species and to molecular M and S forms using PCR techniques. Molecular and biochemical assays were carried out to determine kdr and Ace.1R allelic frequencies and activity of the detoxification enzymes.Throughout the surveys very high levels of mortality to bendiocarb and fenitrothion were observed in An. gambiae s.l. populations. However, high frequencies of resistance to DDT and pyrethroids were seen in both M and S form of An. gambiae s.s. and Anopheles arabiensis. PBO increased the toxicity of permethrin and restored almost full susceptibility to deltamethrin. Anopheles gambiae s.l. mosquitoes from Cotonou and Malanville showed higher oxidase activity compared to the Kisumu susceptible strain in 2009, whereas the esterase activity was higher in the mosquitoes from Bohicon in both 2008 and 2009. A high frequency of 1014F kdr allele was initially showed in An. gambiae from Cotonou and Tori-Bossito whereas it increased in mosquitoes from Bohicon and Malanville during the second year. For the first time the L1014S kdr mutation was found in An. arabiensis in Benin. The ace.1R mutation was almost absent in An. gambiae s.l.Pyrethroid and DDT resistance is widespread in malaria vector in Benin and both metabolic and target site resistance are implicated. Resistance was not correlated with a change of malaria species and/or molecular forms. The 1014S kdr allele was first identified in wild population of An. arabiensis hence confirming the expansion of pyrethroid resistance alleles in Africa.Despite intense national and int
Feeding and resting behaviour of malaria vector, Anopheles arabiensis with reference to zooprophylaxis
Aneth Mahande, Franklin Mosha, Johnson Mahande, Eliningaya Kweka
Malaria Journal , 2007, DOI: 10.1186/1475-2875-6-100
Abstract: Mosquitoes were captured daily using odour-baited entry traps, light traps and hand catch both indoor and in pit traps. Experimental huts were used for release and recapture experiment. The mosquitoes collected were compared in species abundances.Anopheles arabiensis was found to account for over 99% of Anopheles species collected in the study area in Lower Moshi, Northern Tanzania. In experimental release/capture trials conducted at the Mabogini verandah huts, An. arabiensis was found to have higher exophilic tendency (80.7%) compared to Anopheles gambiae (59.7%) and Culex spp. (60.8%). OBET experiments conducted at Mabogini collected a total of 506 An. arabiensis in four different trials involving human, cattle, sheep, goat and pig. Odours from the cattle attracted 90.3% (243) compared to odours from human, which attracted 9.7% (26) with a significant difference at P = 0.005. Odours from sheep, goat and pig attracted 9.7%, 7.2% and 7.3%, respectively. Estimation of HBI in An. arabiensis collected from houses in three lower Moshi villages indicated lower ratios for mosquitoes collected from houses with cattle compared to those without cattles. HBI was also lower in mosquitoes collected outdoors (0.1–0.3) compared to indoor (0.4–0.9).In discussing the results, reference has been made to observation of exophilic, zoophilic and feeding tendencies of An. arabiensis, which are conducive for zooprophylaxis. It is recommended that in areas with a predominant An. arabiensis population, cattle should be placed close to dwelling houses in order to maximize the effects of zooprophylaxis. Protective effects of human from malaria can further be enhanced by keeping cattle in surroundings of residences.Host-odours play a major role in the orientation of nocturnal mosquitoes towards their hosts [1]. Differences in host-preference between mosquito species are, therefore, likely to be reflected in their response to different host odours offered [2]. Carbon dioxide is a major compone
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