Anopheles Moucheti Research Articles

Entomological indicators of Plasmodium species transmission in Goma Tsé-Tsé and Madibou districts, in the Republic of Congo

BackgroundMalaria remains a major public health problem in the Republic of Congo, with Plasmodium falciparum being the deadliest species of Plasmodium in humans. Vector transmission of malaria is poorly studied in the country and no previous report compared rural and urban data. This study aimed to determine the Anopheles fauna and the entomological indices of malaria transmission in the rural and urban areas in the south of Brazzaville, and beyond.MethodsIndoor household mosquitoes capture using electric aspirator was performed in rural and urban areas during raining and dry seasons in 2021. The identification of Anopheles species was done using binocular magnifier and nested-PCR. TaqMan and nested-PCR were used to detect the Plasmodium species in the head/thorax and abdomens of Anopheles. Some entomological indices including the sporozoite infection rate, the entomological inoculation rate and the man biting rate were estimated.ResultsA total of 699 Anopheles mosquitoes were collected: Anopheles gambiae sensu lato (s.l.) (90.7%), Anopheles funestus s.l. (6.9%), and Anopheles moucheti (2.4%). Three species of An. gambiae s.l. were identified including Anopheles gambiae sensu stricto (78.9%), Anopheles coluzzii (15.4%) and Anopheles arabiensis (5.7%). The overall sporozoite infection rate was 22.3% with a predominance of Plasmodium falciparum, followed by Plasmodium malariae and Plasmodium ovale. Anopheles aggressiveness rate was higher in households from rural area (1.1 bites/night) compared to that from urban area (0.8 ib/p/n). The overall entomological inoculation rate was 0.13 ib/p/n. This index was 0.17 ib/p/n and 0.092 ib/p/n in rural and in urban area, respectively, and was similar during the dry (0.18 ib/p/n) and rainy (0.14 ib/p/n) seasons.ConclusionThese findings highlight that malaria transmission remains high in rural and urban area in the south of Republic of Congo despite the ongoing control efforts, thereby indicating the need for more robust interventions.

Limited association between Wolbachia and Plasmodium falciparum infections in natural populations of the major malaria mosquito Anopheles moucheti.

Since the discovery of natural malaria vector populations infected by the endosymbiont bacterium Wolbachia, a renewed interest has arisen for using this bacterium as an alternative for malaria control. Among naturally infected mosquitoes, Anopheles moucheti, a major malaria mosquito in Central Africa, exhibits one of the highest prevalences of Wolbachia infection. To better understand whether this maternally inherited bacterium could be used for malaria control, we investigated Wolbachia influence in An. moucheti populations naturally infected by the malaria parasite Plasmodium falciparum. To this end, we collected mosquitoes in a village from Cameroon, Central Africa, where this mosquito is the main malaria vector. We found that the prevalence of Wolbachia bacterium was almost fixed in the studied mosquito population, and was higher than previously recorded. We also quantified Wolbachia in whole mosquitoes and dissected abdomens, confirming that the bacterium is also elsewhere than in the abdomen, but at lower density. Finally, we analyzed the association of Wolbachia presence and density on P. falciparum infection. Wolbachia density was slightly higher in mosquitoes infected with the malaria parasite than in uninfected mosquitoes. However, we observed no correlation between the P. falciparum and Wolbachia densities. In conclusion, our study indicates that naturally occurring Wolbachia infection is not associated to P. falciparum development within An. moucheti mosquitoes.

A chromosomal reference genome sequence for the malaria mosquito, Anophelesmoucheti, Evans, 1925.

We present a genome assembly from an individual male Anopheles moucheti (the malaria mosquito; Arthropoda; Insecta; Diptera; Culicidae), from a wild population in Cameroon. The genome sequence is 271 megabases in span. The majority of the assembly is scaffolded into three chromosomal pseudomolecules with the X sex chromosome assembled. The complete mitochondrial genome was also assembled and is 15.5 kilobases in length.

Spatial distribution and ecological niche modeling of geographical spread of Anopheles gambiae complex in Nigeria using real time data

The need for evidence-based data, to inform policy decisions on malaria vector control interventions in Nigeria, necessitated the establishment of mosquito surveillance sites in a few States in Nigeria. In order to make evidence-based-decisions, predictive studies using available data becomes imperative. We therefore predict the distribution of the major members of the Anopheles gambiae s.l. in Nigeria. Immature stages of Anopheles were collected from 72 study locations which span throughout the year 2020 resulted in the identification of over 60,000 Anopheline mosquitoes. Of these, 716 breeding sites were identified with the presence of one or more vector species from the An. gambiae complex and were subsequently used for modelling the potential geographical distribution of these important malaria vectors. Maximum Entropy (MaxEnt) distribution modeling was used to predict their potentially suitable vector habitats across Nigeria. A total of 23 environmental variables (19 bioclimatic and four topographic) were used in the model resulting in maps of the potential geographical distribution of three dominant vector species under current climatic conditions. Members of the An. gambiae complex dominated the collections (98%) with Anopheles stephensi, Anopheles coustani, Anopheles funestus, Anopheles moucheti, Anopheles nilli also present. An almost equal distribution of the two efficient vectors of malaria, An. gambiae and Anopheles coluzzii, were observed across the 12 states included in the survey. Anopheles gambiae and Anopheles coluzzii had almost equal, well distributed habitat suitability patterns with the latter having a slight range expansion. However, the central part of Nigeria (Abuja) and some highly elevated areas (Jos) in the savannah appear not suitable for the proliferation of these species. The most suitable habitat for Anopheles arabiensis was mainly in the South-west and North-east. The results of this study provide a baseline allowing decision makers to monitor the distribution of these species and establish a management plan for future national mosquito surveillance and control programs in Nigeria.

High vector diversity and malaria transmission dynamics in five sentinel sites in Cameroon

BackgroundMalaria remains one of the main causes of morbidity and mortality in Cameroon. To inform vector control intervention decision making, malaria vector surveillance was conducted monthly from October 2018 to September 2020 in five selected sentinel sites (Gounougou and Simatou in the North, and Bonabéri, Mangoum and Nyabessang in the South).MethodsHuman landing catches (HLCs), U.S. Centers for Disease Control and Prevention (CDC) light traps, and pyrethrum spray catches (PSCs) were used to assess vector density, species composition, human biting rate (HBR), endophagic index, indoor resting density (IRD), parity, sporozoite infection rates, entomological inoculation rate (EIR), and Anopheles vectorial capacity.ResultsA total of 139,322 Anopheles mosquitoes from 18 species (or 21 including identified sub-species) were collected across all sites. Out of the 18 species, 12 were malaria vectors including Anopheles gambiae sensu lato (s.l.), Anopheles funestus s.l.., Anopheles nili, Anopheles moucheti, Anopheles paludis, Anopheles demeilloni, Anopheles. pharoensis, Anopheles ziemanni, Anopheles multicinctus, Anopheles tenebrosus, Anopheles rufipes, and Anopheles marshallii. Anopheles gambiae s.l. remains the major malaria vector (71% of the total Anopheles) collected, though An. moucheti and An. paludis had the highest sporozoite rates in Nyabessang. The mean indoor HBR of Anopheles ranged from 11.0 bites/human/night (b/h/n) in Bonabéri to 104.0 b/h/n in Simatou, while outdoors, it varied from 24.2 b/h/n in Mangoum to 98.7 b/h/n in Simatou. Anopheles gambiae s.l. and An. moucheti were actively biting until at least 8:00 a.m. The mean Anopheles IRD was 17.1 females/room, and the parity rate was 68.9%. The mean EIRs for each site were 55.4 infective bites/human/month (ib/h/m) in Gounougou, 99.0 ib/h/m in Simatou, 51.2 ib/h/m in Mangoum, 24.4 ib/h/m in Nyabessang, and 18.1 ib/h/m in Bonabéri. Anopheles gambiae s.l. was confirmed as the main malaria vector with the highest vectorial capacity in all sites based on sporozoite rate, except in Nyabessang.ConclusionThese findings highlight the high malaria transmission occurring in Cameroon and will support the National Malaria Control Program to design evidence-based malaria vector control strategies, and deployment of effective and integrated vector control interventions to reduce malaria transmission and burden in Cameroon, where several Anopheles species could potentially maintain year-round transmission.

Role of Pfs47 in the dispersal of ancestral Plasmodium falciparum malaria through adaptation to different anopheline vectors

Plasmodium falciparum malaria originated when Plasmodium praefalciparum, a gorilla malaria parasite transmitted by African sylvan anopheline mosquitoes, adapted to humans. Pfs47, a protein on the parasite surface mediates P. falciparum evasion of the mosquito immune system by interacting with a midgut receptor and is critical for Plasmodium adaptation to different anopheline species. Genetic analysis of 4,971 Pfs47 gene sequences from different continents revealed that Asia and Papua New Guinea harbor Pfs47 haplotypes more similar to its ortholog in P. praefalciparum at sites that determine vector compatibility, suggesting that ancestral P. falciparum readily adapted to Asian vectors. Consistent with this observation, Pfs47-receptor gene sequences from African sylvan malaria vectors, such as Anopheles moucheti and An. marshallii, were found to share greater similarity with those of Asian vectors than those of vectors of the African An. gambiae complex. Furthermore, experimental infections provide direct evidence that transformed P. falciparum parasites carrying Pfs47 orthologs of P. praefalciparum or P. reichenowi were more effective at evading the immune system of the Asian malaria vector An. dirus than An. gambiae. We propose that high compatibility of ancestral P. falciparum Pfs47 with the receptors of Asian vectors facilitated the early dispersal of human malaria to the Asian continent, without having to first adapt to sub-Saharan vectors of the An. gambiae complex.

Wolbachia endosymbionts in two Anopheles species indicates independent acquisitions and lack of prophage elements

Wolbachia is a genus of obligate bacterial endosymbionts that infect a diverse range of arthropod species as well as filarial nematodes, with its single described species, Wolbachia pipientis , divided into several ‘supergroups’ based on multilocus sequence typing. Wolbachia strains in mosquitoes have been shown to inhibit the transmission of human pathogens, including Plasmodium malaria parasites and arboviruses. Despite their large host range, Wolbachia strains within the major malaria vectors of the Anopheles gambiae and Anopheles funestus complexes appear at low density, established solely on PCR-based methods. Questions have been raised as to whether this represents a true endosymbiotic relationship. However, recent definitive evidence for two distinct, high-density strains of supergroup B Wolbachia within Anopheles demeilloni and Anopheles moucheti has opened exciting possibilities to explore naturally occurring Wolbachia endosymbionts in Anopheles for biocontrol strategies to block Plasmodium transmission. Here, we utilize genomic analyses to demonstrate that both Wolbachia strains have retained all key metabolic and transport pathways despite their smaller genome size, with this reduction potentially attributable to degenerated prophage regions. Even with this reduction, we confirmed the presence of cytoplasmic incompatibility (CI) factor genes within both strains, with wAnD maintaining intact copies of these genes while the cifB gene was interrupted in wAnM, so functional analysis is required to determine whether wAnM can induce CI. Additionally, phylogenetic analysis indicates that these Wolbachia strains may have been introduced into these two Anopheles species via horizontal transmission events, rather than by ancestral acquisition and subsequent loss events in the Anopheles gambiae species complex. These are the first Wolbachia genomes, to our knowledge, that enable us to study the relationship between natural strain Plasmodium malaria parasites and their anopheline hosts.

Review of Issues on Residual Malaria Transmission

Residual malaria transmission is the actual maintained inoculation of Plasmodium, in spite of a well-designed and implemented vector control programs, and is of great concern for malaria elimination. Residual malaria transmission occurs under several possible circumstances, among which the presence of exophilic vector species, such as Anopheles dirus, or indoor- and outdoor-biting vectors, such as Anopheles nili, or specific behavior, such as feeding on humans indoors, then resting or leaving the house the same night (such as Anopheles moucheti) or also changes in behavior induced by insecticides applied inside houses, such as the well-known deterrent effect of permethrin-treated nets or the irritant effect of DDT. The use of insecticides may change the composition of local Anopheles populations, such as A. arabiensis taking up the place of A. gambiae in Senegal, A. aquasalis replacing A. darlingi in Guyana, or A. harrisoni superseding A. minimus in Vietnam. The change in behavior, such as biting activity earlier than usually reported—for example, Anopheles funestus after a large-scale distribution of long-lasting insecticidal nets—or insecticide resistance, in particular the current spread of pyrethroid resistance, could hamper the efficacy of classic pyrethroid-treated long-lasting insecticidal nets and maintained transmission. These issues must be well documented in every situation to elaborate, implement, monitor, and evaluate tailored vector control programs, keeping in mind that they must be conceived as integrated programs with several well and appropriately coordinated approaches, combining entomological but also parasitological, clinical, and social methods and analyses. A successful integrated vector control program must then be designed to reduce transmission and incidence rates of malaria morbidity and overall mortality.

Stable high-density and maternally inherited Wolbachia infections in Anopheles moucheti and Anopheles demeilloni mosquitoes

SummaryWolbachia, a widespread bacterium that can reduce pathogen transmission in mosquitoes, has recently been reported to be present in Anopheles (An.) species. In wild populations of the An. gambiae complex, the primary vectors of Plasmodium malaria in Sub-Saharan Africa, Wolbachia DNA sequences at low density and infection frequencies have been detected. As the majority of studies have used highly sensitive nested PCR as the only method of detection, more robust evidence is required to determine whether Wolbachia strains are established as endosymbionts in Anopheles species. Here, we describe high-density Wolbachia infections in geographically diverse populations of An. moucheti and An. demeilloni. Fluorescent in situ hybridization localized a heavy infection in the ovaries of An. moucheti, and maternal transmission was observed. Genome sequencing of both Wolbachia strains obtained genome depths and coverages comparable to those of other known infections. Notably, homologs of cytoplasmic incompatibility factor (cif) genes were present, indicating that these strains possess the capacity to induce the cytoplasmic incompatibility phenotype, which allows Wolbachia to spread through host populations. These strains should be further investigated as candidates for use in Wolbachia biocontrol strategies in Anopheles aiming to reduce the transmission of malaria.

Member species of the Anopheles gambiae complex can be misidentified as Anopheles leesoni

BackgroundAccurate Anopheles species identification is key for effective malaria vector control. Identification primarily depends on morphological analysis of field samples as well as molecular species-specific identifications. During an intra-laboratory assessment (proficiency testing) of the Anopheles funestus group multiplex PCR assay, it was noted that Anopheles arabiensis can be misidentified as Anopheles leesoni, a zoophilic member of the An. funestus group. The aim of this project was, therefore, to ascertain whether other members of the Anopheles gambiae complex can also be misidentified as An. leesoni when using the standard An. funestus multiplex PCR.MethodsThe An. funestus multiplex PCR was used to amplify DNA from An. gambiae complex specimens. These included specimens from the laboratory colonies and field samples from the Democratic Republic of Congo. Amplified DNA from these specimens, using the universal (UV) and An. leesoni species-specific primers (LEES), were sequence analysed. Additionally, An. leesoni DNA was processed through the diagnostic An. gambiae multiplex PCR to determine if this species can be misidentified as a member of the An. gambiae complex.ResultsLaboratory-colonized as well as field-collected samples of An. arabiensis, An. gambiae, Anopheles merus, Anopheles quadriannulatus, Anopheles coluzzii as well as Anopheles moucheti produced an amplicon of similar size to that of An. leesoni when using an An. funestus multiplex PCR. Sequence analysis confirmed that the UV and LEES primers amplify a segment of the ITS2 region of members of the An. gambiae complex and An. moucheti. The reverse was not true, i.e. the An. gambiae multiplex PCR does not amplify DNA from An. leesoni.ConclusionThis investigation shows that An. arabiensis, An. gambiae, An. merus, An. quadriannulatus, An. coluzzii and An. moucheti can be misidentified as An. leesoni when using An. funestus multiplex PCR. This shows the importance of identifying specimens using standard morphological dichotomous keys as far as possible prior to the use of appropriate PCR-based identification methods. Should there be doubt concerning field-collected specimens molecularly identified as An. leesoni, the An. gambiae multiplex PCR and sequencing of the internal transcribed spacer 2 (ITS2) can be used to eliminate false identifications.

Ecology and Contribution of Anopheles hancocki Edwards, 1929 in Malaria Transmission in a Village of South Cameroon Forest Block

Anopheles hancocki is one of the secondary vectors of malaria whose larval ecology in the South Cameroonian forest block is still unknown. This information is however fundamental for developing efficient and sustainable control strategies against this mosquito in localities where it acts as a disease vector. The present study describes the larval ecology of A. hancocki and its contribution in malaria transmission in a riverbank village of the Ayos Health District. Mosquito sampling took place in 2018 on a quarterly rate, combining the dipping method for larval collection with adult mosquito capture on volunteers. For each of the breeding sites, physicochemical characteristics were measured and larvae were collected and reared to adult. Molecular alongside morpho-taxonomic techniques were used for the identification of mosquito species. Physiological age was determined based on the appearance of their ovarian tracheoles and CSP Elisa test was used to assess infectivity. In total, 3,618 adult mosquitoes belonging to seven species were collected in the study area, namely A. hancocki, Anopheles gambiae, Anopheles moucheti, Mansonia africana, Culex pipiens quinquefasciatus, Aedes albopictus and Aedes aegypti. Breeding sites of A. hancocki were similar to those of A. gambiae. However, the total dissolved solids and conductivity values were significantly higher in A. gambiae breeding sites than in those of A. hancocki. A. hancocki was the most aggressive mosquito species and represented 45.6% of the local aggressive culicidofauna. Male species' nocturnal cycle of aggression showed maximum activity between 8 pm and 10 pm. Females of this species were significantly older than those of A. gambiae and contributed to 40% of malaria transmission in the locality with an average annual Entomological Inoculation Rate (EIR) of 2.92 ib/p/year lower than that of A. gambiae (3.65 ib/p/year). Except few differences, ecological requirements for the development of A. hancocki larvae are similar to that of A. gambiae. A. hancocki contributes to the perennial transmission of malaria in the Ayos area; implementation of vector control strategies is therefore needed.

Extensive genetic diversity among populations of the malaria mosquito Anopheles moucheti revealed by population genomics

Malaria vectors are exposed to intense selective pressures due to large-scale intervention programs that are underway in most African countries. One of the current priorities is therefore to clearly assess the adaptive potential of Anopheline populations, which is critical to understand and anticipate the response mosquitoes can elicit against such adaptive challenges. The development of genomic resources that will empower robust examinations of evolutionary changes in all vectors including currently understudied species is an inevitable step toward this goal. Here we constructed double-digest Restriction Associated DNA (ddRAD) libraries and generated 6461 Single Nucleotide Polymorphisms (SNPs) that we used to explore the population structure and demographic history of wild-caught Anopheles moucheti from Cameroon. The genome-wide distribution of allelic frequencies among samples best fitted that of an old population at equilibrium, characterized by a weak genetic structure and extensive genetic diversity, presumably due to a large long term effective population size. Estimates of FST and Linkage Disequilibrium (LD) across SNPs reveal a very low genetic differentiation throughout the genome and the absence of segregating LD blocks among populations, suggesting an overall lack of local adaptation. Our study provides the first investigation of the genetic structure and diversity in An. moucheti at the genomic scale. We conclude that, despite a weak genetic structure, this species has the potential to challenge current vector control measures and other rapid anthropogenic and environmental changes thanks to its great genetic diversity.

Ape malaria transmission and potential for ape-to-human transfers in Africa

Recent studies have highlighted the large diversity of malaria parasites infecting African great apes (subgenus Laverania) and their strong host specificity. Although the existence of genetic incompatibilities preventing the cross-species transfer may explain host specificity, the existence of vectors with a high preference for a determined host represents another possibility. To test this hypothesis, we undertook a 15-mo-long longitudinal entomological survey in two forest regions of Gabon, where wild apes live, at different heights under the canopy. More than 2,400 anopheline mosquitoes belonging to 18 species were collected. Among them, only three species of Anopheles were found infected with ape Plasmodium: Anopheles vinckei, Anopheles moucheti, and Anopheles marshallii Their role in transmission was confirmed by the detection of the parasites in their salivary glands. Among these species, An. vinckei showed significantly the highest prevalence of infection and was shown to be able to transmit parasites of both chimpanzees and gorillas. Transmission was also shown to be conditioned by seasonal factors and by the heights of capture under the canopy. Moreover, human landing catches of sylvan Anopheles demonstrated the propensity of these three vector species to feed on humans when available. Our results suggest therefore that the strong host specificity observed in the Laveranias is not linked to a specific association between the vertebrate host and the vector species and highlight the potential role of these vectors as bridge between apes and humans.

Polymorphic chromosomal inversions in Anopheles moucheti, a major malaria vector in Central Africa

Anopheles moucheti Evans (Diptera: Culicidae) is a major vector of malaria in forested areas of Central Africa. However, few genetic tools are available for this species. The present study represents the first attempt to characterize chromosomes in An. moucheti females collected in Cameroon. Ovarian nurse cells contained polytene chromosomes, which were suitable for standard cytogenetic applications. The presence of three polymorphic chromosomal inversions in An. moucheti was revealed. Two of these inversions were located on the 2R chromosome arm. The homology between the 2R chromosome arms of An. moucheti and Anopheles gambiae Giles was established by fluorescent in situ hybridization of six An. gambiae genic sequences. Mapping of the probes on chromosomes of An. moucheti detected substantial gene order reshuffling between the two species. The presence of polytene chromosomes and polymorphic inversions in An. moucheti provides a new basis for further population genetic, taxonomic and ecological studies of this neglected malaria vector.

Abundance and diversity of Anopheles species (Diptera: Culicidae) associated with malaria transmission in human dwellings in rural and urban communities in Oyo State, Southwestern Nigeria

Mosquito samples were collected from rural and urban communities in three selected major towns in Southwestern Nigeria to determine the impact of urbanization on the diversity and abundance of Anopheles species associated with malaria transmission in human habitations. A total of ten Anopheles species were identified in the rural communities, while eight Anopheles species were identified in the urban communities. Out of the ten Anopheles species identified, only four species, Anopheles gambiae (Giles), Anopheles funestus (Giles), Anopheles moucheti (Evans), and Anopheles nili (Theobald), were established to be vectors of malaria occurring in greater than 50% of the rural communities. Only A. gambiae occurred in all the urban communities, while the other three major vectors occurred in not more than 20% of the urban communities. Margalef's and Shannon-Wiener indices showed that diversity and species richness were higher in the rural compared to the urban. Comprehensive information on malaria vector abundance and diversity in rapidly changing communities is an important tool in planning and implementing successful vector control programs.

Anopheles moucheti and Anopheles vinckei are candidate vectors of ape Plasmodium parasites, including Plasmodium praefalciparum in Gabon.

During the last four years, knowledge about the diversity of Plasmodium species in African great apes has considerably increased. Several new species were described in chimpanzees and gorillas, and some species that were previously considered as strictly of human interest were found to be infecting African apes. The description in gorillas of P. praefalciparum, the closest relative of P. falciparum which is the main malignant agent of human malaria, definitively changed the way we understand the evolution and origin of P. falciparum. This parasite is now considered to have appeared recently, following a cross-species transfer from gorillas to humans. However, the Plasmodium vector mosquito species that have served as bridge between these two host species remain unknown. In order to identify the vectors that ensure ape Plasmodium transmission and evaluate the risk of transfer of these parasites to humans, we carried out a field study in Gabon to capture Anopheles in areas where wild and semi-wild ape populations live. We collected 1070 Anopheles females belonging to 15 species, among which An. carnevalei, An. moucheti and An. marshallii were the most common species. Using mtDNA-based PCR tools, we discovered that An. moucheti, a major human malaria vector in Central Africa, could also ensure the natural transmission of P. praefalciparum among great apes. We also showed that, together with An. vinckei, An. moucheti was infected with P. vivax-like parasites. An. moucheti constitutes, therefore, a major candidate for the transfer of Plasmodium parasites from apes to humans.

Habitat suitability and ecological niche profile of major malaria vectors in Cameroon.

BackgroundSuitability of environmental conditions determines a species distribution in space and time. Understanding and modelling the ecological niche of mosquito disease vectors can, therefore, be a powerful predictor of the risk of exposure to the pathogens they transmit. In Africa, five anophelines are responsible for over 95% of total malaria transmission. However, detailed knowledge of the geographic distribution and ecological requirements of these species is to date still inadequate.MethodsIndoor-resting mosquitoes were sampled from 386 villages covering the full range of ecological settings available in Cameroon, Central Africa. Using a predictive species distribution modeling approach based only on presence records, habitat suitability maps were constructed for the five major malaria vectors Anopheles gambiae, Anopheles funestus, Anopheles arabiensis, Anopheles nili and Anopheles moucheti. The influence of 17 climatic, topographic, and land use variables on mosquito geographic distribution was assessed by multivariate regression and ordination techniques.ResultsTwenty-four anopheline species were collected, of which 17 are known to transmit malaria in Africa. Ecological Niche Factor Analysis, Habitat Suitability modeling and Canonical Correspondence Analysis revealed marked differences among the five major malaria vector species, both in terms of ecological requirements and niche breadth. Eco-geographical variables (EGVs) related to human activity had the highest impact on habitat suitability for the five major malaria vectors, with areas of low population density being of marginal or unsuitable habitat quality. Sunlight exposure, rainfall, evapo-transpiration, relative humidity, and wind speed were among the most discriminative EGVs separating "forest" from "savanna" species.ConclusionsThe distribution of major malaria vectors in Cameroon is strongly affected by the impact of humans on the environment, with variables related to proximity to human settings being among the best predictors of habitat suitability. The ecologically more tolerant species An. gambiae and An. funestus were recorded in a wide range of eco-climatic settings. The other three major vectors, An. arabiensis, An. moucheti, and An. nili, were more specialized. Ecological niche and species distribution modelling should help improve malaria vector control interventions by targeting places and times where the impact on vector populations and disease transmission can be optimized.

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

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

A pre-intervention study of malaria vector abundance in Rio Muni, Equatorial Guinea: Their role in malaria transmission and the incidence of insecticide resistance alleles

BackgroundFollowing the success of the malaria control intervention on the island of Bioko, malaria control by the use of indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLITN) was extended to Rio Muni, on the mainland part of Equatorial Guinea. This manuscript reports on the malaria vectors present and the incidence of insecticide resistant alleles prior to the onset of the programme.MethodsAnopheles mosquitoes were captured daily using window traps at 30 sentinel sites in Rio Muni, from December 2006 to July 2007. The mosquitoes were identified to species and their sporozoite rates, knockdown resistance (kdr) and acetylcholinesterase (AChE) sensitivity measured, to define the role of vector species in malaria transmission and their potential susceptibility to insecticides.ResultsA total of 6,162 Anopheles mosquitoes were collected of which 4,808 were morphologically identified as Anopheles gambiae s.l., 120 Anopheles funestus, 1,069 Anopheles moucheti, and 165 Anopheles nili s.l.. Both M and S molecular forms of Anopheles gambiae s.s. and Anopheles melas were identified. Anopheles ovengensis and Anopheles carnevalei were the only two members of the An. nili group to be identified. Using the species-specific sporozoite rates and the average number of mosquitoes per night, the number of infective mosquitoes per trap per 100 nights for each species complex was calculated as a measure of transmission risk. Both kdr-w and kdr-e alleles were present in the S-form of An. gambiae s.s. (59% and 19% respectively) and at much lower frequencies in the M-form (9.7% and 1.8% respectively). The kdr-w and kdr-e alleles co-occurred in 103 S-form and 1 M-form specimens. No insensitive AChE was detected.ConclusionAnopheles gambiae s.s, a member of the Anopheles gambiae complex was shown to be the major vector in Rio Muni with the other three groups playing a relatively minor role in transmission. The demonstration of a high frequency of kdr alleles in mosquito populations before the onset of a malaria control programme shows that continuous entomological surveillance including resistance monitoring will be of critical importance to ensure the chosen insecticide remains effective.

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

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