Anopheles gambiae salivary protein expression modulated by wild Plasmodium falciparum infection: Highlighting of new antigenic peptides as candidates of An. gambiae bites

Background: Malaria is the major parasitic disease worldwide caused by Plasmodium infection. The objective of integrated malaria control programs is to decrease malaria transmission, which needs specific tools to be accurately assessed. In areas where the transmission is low or has been substantially reduced, new complementary tools have to be developed to improve surveillance. A recent approach, based on the human antibody response to Anopheles salivary proteins, has been shown to be efficient in evaluating human exposure to Anopheles bites. The aim of the present study was to identify new An. gambiae salivary proteins as potential candidate biomarkers of human exposure to P. falciparum-infective bites. Methods: Experimental infections of An. gambiae by wild P. falciparum were carried out in semi-field conditions. Then a proteomic approach, combining 2D-DIGE and mass spectrometry, was used to identify the overexpressed salivary proteins in infected salivary glands compared to uninfected An. gambiae controls. Subsequently, a peptide design of each potential candidate was performed in silico and their antigenicity was tested by an epitope-mapping technique using blood from individuals exposed to Anopheles bites. Results: Five salivary proteins (gSG6, gSG1b, TRIO, SG5 and long form D7) were overexpressed in the infected salivary glands. Eighteen peptides were designed from these proteins and were found antigenic in children exposed to the Anopheles bites. Moreover, the results showed that the presence of wild P. falciparum in salivary glands modulates the expression of several salivary proteins and also appeared to induce post-translational modifications. Conclusions: This study is, to our knowledge, the first that compares the sialome of An. gambiae both infected and not infected by wild P. falciparum, making it possible to mimic the natural conditions of infection. This is a first step toward a better understanding of the close interactions between the parasite and the salivary gland of mosquitoes. In addition, these results open the way to define biomarkers of infective bites of Anopheles, which could, in the future, improve the estimation of malaria transmission and the evaluation of malaria vector control tools. (Résumé d'auteur

Bionomics of Anopheline species and malaria transmission dynamics along an altitudinal transect in Western Cameroon

<p>Abstract</p> <p>Background</p> <p>Highland areas of Africa are mostly malaria hypoendemic, due to climate which is not appropriate for anophelines development and their reproductive fitness. In view of designing a malaria control strategy in Western Cameroon highlands, baseline data on anopheline species bionomics were collected.</p> <p>Methods</p> <p>Longitudinal entomological surveys were conducted in three localities at different altitudinal levels. Mosquitoes were captured when landing on human volunteers and by pyrethrum spray catches. Sampled <it>Anopheles </it>were tested for the presence of <it>Plasmodium </it>circumsporozoite proteins and their blood meal origin with ELISA. Entomological parameters of malaria epidemiology were assessed using Mac Donald's formula.</p> <p>Results</p> <p>Anopheline species diversity and density decreased globally from lowland to highland. The most aggressive species along the altitudinal transect was <it>Anopheles gambiae </it>s.s. of S molecular form, followed in the lowland and on the plateau by <it>An. funestus</it>, but uphill by <it>An. hancocki</it>. <it>An. gambiae </it>and <it>An. ziemanni </it>exhibited similar seasonal biting patterns at the different levels, whereas different features were observed for <it>An. funestus</it>. Only indoor resting species could be captured uphill; it is therefore likely that endophilic behaviour is necessary for anophelines to climb above a certain threshold. Of the ten species collected along the transect, only <it>An. gambiae </it>and <it>An. funestus </it>were responsible for malaria transmission, with entomological inoculation rates (EIR) of 90.5, 62.8 and zero infective bites/human/year in the lowland, on the plateau and uphill respectively. The duration of gonotrophic cycle was consistently one day shorter for <it>An. gambiae </it>as compared to <it>An. funestus </it>at equal altitude. Altitudinal climate variations had no effect on the survivorship and the subsequent life expectancy of the adult stage of these malaria vectors, but most probably on aquatic stages. On the contrary increasing altitude significantly extended the duration of gonotrophic cycle and reduced: the EIR, their preference to human blood and consequently the malaria stability index.</p> <p>Conclusion</p> <p>Malaria epidemiological rooting in the outskirts of Western Cameroon highlands evolves with increasing altitude, gradually from stable to unstable settings. This suggests a potential risk of malaria epidemic in highlands, and the need for a continuous epidemiological surveillance.</p

Survival and emergence of immature Anopheles arabiensis mosquitoes in market-gardener wells in Dakar, Senegal

#Anopheles arabiensis est la seule espèce du complex #An. gambiae rencontrée dans les puits maraîchers (localement dénommés céanes) creusés dans la région de Dakar. Dans le but de relier les nombres de stades préimaginaux et de moustiques émergents, des dénombrements de population ont été réalisés dans huit puits dans lesquels #An. arabiensis a été le seul #Culicidae rencontré. La densité moyenne des stades préimagninaux a été évaluée par deux méthodes d'échantillonage : la méthode du dipping avec un plateau à raison de 50 coups de plateau par puits, et la méthode du quadrat avec un cadre de 1 m2 à raison de deux ou trois quadrats par puits. Le nombre absolu d'adultes émergents a été obtenu en recouvrant chaque puits d'une moustiquaire et en collectant les moustiques néonates ainsi piégés. La technique du dipping s'est révélée plus rapide et plus opérationnelle que la technique du quadrat. Les estimations des densités de chacun des quatre stades larvaires n'ont pas différé significativement entre les méthodes du dipping et du quadrat. Mais la densité des nymphes a été sous-estimée avec le dipping. La présence de moustiquaires-pièges sur les puits a significativement augmenté l'émergence, aussi, l'évolution de l'émergence des adultes a seulement été possible lors de la première journée de mise en place des moustiquaires. Le nombre total de stades préimaginaux par puits a été significativement corrélé au nombre de moustiques émergeant. En moyenne, le nombre d'adultes émergents quotidiennement d'un puits a représenté 5% du nombre total des larves. Les stades larvaires 1-4 et nymphal, estimés par quadrat, ont respectivement représenté 29%, 28%, 22%, 16% et 5% (total = 100%). Compte tenue de la durée moyenne de chaque stade préimaginal et du nombre de moustiques émergeant quotidiennement, l'équation de la courbe de survie depuis l'éclosion (exclue) jusqu'à l'émergence inclue a été : y = 427,2-136,8 Log x... (D'après résumé d'auteur

Description and bionomics of Anopheles (Cellia) ovengensis (Diptera: Culicidae), a new malaria vector species of the Anopheles nili group from south Cameroon

Mosquito species of the Anopheles nili group (Diptera: Culicidae) transmit malaria to humans along rivers in Africa. To date, the An. nili group includes the species Anopheles nili s.s. and its pale-winged variant known as the "Congo form," Anopheles somalicus and Anopheles carnevalei. Larval and adult mosquito collections in the forest region of Campo, in southern Cameroon, uncovered an additional morphological variant provisionally called "Oveng form" that was subsequently found to be genetically distinct from the other members of the An. nili group. In this study, we provide further biological data that characterizes this new taxon and justifies elevation to specific rank. We propose calling this new species Anopheles ovengensis, after its geographical origin. We present a morphological description of the adult female and fourth instars and original data on the biology, ecology, and role as a human malaria vector of this new species in its type location. We provide dichotomous keys for identification of adult females and fourth instars that can be used at least in tropical areas of west and central Africa

Correction: Application of a qPCR Assay in the Investigation of Susceptibility to Malaria Infection of the M and S Molecular Forms of An. gambiae s.s. in Cameroon.

[This corrects the article DOI: 10.1371/journal.pone.0054820.]

The Rare, the Best: Spread of Antimalarial-Resistant Plasmodium falciparum Parasites by Anopheles Mosquito Vectors

International audienceThe emergence of resistance to antimalarials has prompted the steady switch to novel therapies for decades. Withdrawal of antimalarials, such as chloroquine in sub-Saharan Africa in the late 1990s, led to rapid declines in the prevalence of resistance markers after a few years, raising the possibility of reintroducing them for malaria treatment. Here, we provide evidence that the mosquito vector plays a crucial role in maintaining parasite genetic diversity. We followed the transmission dynamics of Plasmodium falciparum parasites through its vector in natural infections from gametocytes contained in the blood of asymptomatic volunteers until sporozoites subsequently developed in the mosquito salivary glands. We did not find any selection of the mutant or wild-type pfcrt 76 allele during development in the Anopheles mosquito vector. However, microsatellite genotyping indicated that minority genotypes were favored during transmission through the mosquito. The analysis of changes in the proportions of mutant and wild-type pfcrt 76 alleles showed that, regardless of the genotype, the less-represented allele in the gametocyte population was more abundant in mosquito salivary glands, indicating a selective advantage of the minority allele in the vector. Selection of minority genotypes in the vector would explain the persistence of drug-resistant alleles in the absence of drug pressure in areas with high malaria endemicity and high genetic diversity. Our results may have important epidemiological implications, as they predict the rapid re-emergence and spread of resistant genotypes if antimalarials that had previously selected resistant parasites are reintroduced for malaria prevention or treatment.IMPORTANCE Drug selection pressure in malaria patients is the cause of the emergence of resistant parasites. Resistance imposes a fitness cost for parasites in untreated infections, so withdrawal of the drug leads to the return of susceptible parasites. Little is known about the role of the malaria vector in this phenomenon. In an experimental study conducted in Cameroon, an area of high malaria transmission, we showed that the vector did not favor the parasites based on sensitivity or resistance criteria, but it did favor the selection of minority clones. This finding shows that the vector increases the diversity of plasmodial populations and could play an important role in falciparum malaria epidemiology by maintaining resistant clones despite the absence of therapeutic pressure.