Different distribution of malaria parasite in left and right extremities of vertebrate hosts translates into differences in parasite transmission

International audienceMalaria, a vector-borne disease caused by Plasmodium spp., remains a major global cause of mortality. Optimization of disease control strategies requires a thorough understanding of the processes underlying parasite transmission. While the number of transmissible stages (gametocytes) of Plasmodium in blood is frequently used as an indicator of host-to-mosquito transmission potential, this relationship is not always clear. Significant effort has been made in developing molecular tools that improve gametocyte density estimation and therefore prediction of mosquito infection rates. However a significant level of uncertainty around estimates remains. The weakness in the relationship between gametocyte burden, measured from a blood sample, and the mosquito infection rate could be explained by a non-homogeneous distribution of gametocytes in the bloodstream. The estimated gametocyte density would then only be a single snapshot that does not reflect the host infectivity. This aspect of Plasmodium infection, however, remains largely neglected. In both humans and birds, we found here that the gametocyte densities differed depending on which side of the body the sample was taken, suggesting that gametocytes are not homogeneously distributed within the vertebrate host. We observed a fluctuating asymmetry, in other words, the extremity of the body with the highest density of parasites is not always the same from one individual to another. An estimation of gametocyte density from only one blood sample, as is commonly measured, could, therefore, over-or underestimated the infectivity of gametocyte carriers. This might have important consequences on the epidemiology of the disease since we show that this variation influences host-to-mosquito transmission. Vectors fed on the least infected body part had a lower parasite burden than those fed on the most infected part. The heterogeneous distribution of gametocytes in bloodstream should be considered to improve diagnosis and test new malaria control strategies

West African Anopheles Gambiae Mosquitoes Harbor a Taxonomically Diverse Virome Including New Insect-Specific Flaviviruses, Mononegaviruses, and Totiviruses

Anopheles gambiae are a major vector of malaria in sub-Saharan Africa. Viruses that naturally infect these mosquitoes may impact their physiology and ability to transmit pathogens. We therefore used metagenomics sequencing to search for viruses in adult Anopheles mosquitoes collected from Liberia, Senegal, and Burkina Faso. We identified a number of virus and virus-like sequences from mosquito midgut contents, including 14 coding-complete genome segments and 26 partial sequences. The coding-complete sequences define new viruses in the order Mononegavirales, and the families Flaviviridae, and Totiviridae. The identification of a flavivirus infecting Anopheles mosquitoes broadens our understanding of the evolution and host range of this virus family. This study increases our understanding of virus diversity in general, begins to define the virome of a medically important vector in its natural setting, and lays groundwork for future studies examining the potential impact of these viruses on anopheles biology and disease transmission

Decreased motivation in the use of insecticide-treated nets in a malaria endemic area in Burkina Faso

<p>Abstract</p> <p>Background</p> <p>The use of insecticide-treated nets (ITN) is an important tool in the Roll Back Malaria (RBM) strategy. For ITNs to be effective they need to be used correctly. Previous studies have shown that many factors, such as wealth, access to health care, education, ethnicity and gender, determine the ownership and use of ITNs. Some studies showed that free distribution and public awareness campaigns increased the rate of use. However, there have been no evaluations of the short- and long-term impact of such motivation campaigns. A study carried out in a malaria endemic area in south-western Burkina Faso indicated that this increased use declined after several months. The reasons were a combination of the community representation of malaria, the perception of the effectiveness and usefulness of ITNs and also the manner in which households are organized by day and by night.</p> <p>Methods</p> <p>PermaNet 2.0^®and Olyset^®were distributed in 455 compounds at the beginning of the rainy season. The community was educated on the effectiveness of nets in reducing malaria and on how to use them. To assess motivation, qualitative tools were used: one hundred people were interviewed, two hundred houses were observed directly and two houses were monitored monthly throughout one year.</p> <p>Results</p> <p>The motivation for the use of bednets decreased after less than a year. Inhabitants' conception of malaria and the inconvenience of using bednets in small houses were the major reasons. Acceptance that ITNs were useful in reducing malaria was moderated by the fact that mosquitoes were considered to be only one of several factors which caused malaria. The appropriate and routine use of ITNs was adversely affected by the functional organization of the houses, which changed as between day and night. Bednets were not used when the perceived benefits of reduction in mosquito nuisance and of malaria were considered not to be worth the inconvenience of daily use.</p> <p>Conclusion</p> <p>In order to bridge the gap between possession and use of bednets, concerted efforts are required to change behaviour by providing accurate information, most particularly by convincing people that mosquitoes are the only source of malaria, whilst recognising that there are other diseases with similar symptoms, caused in other ways. The medical message must underline the seriousness of malaria and the presence of the malaria vector in the dry season as well as the wet, in order to encourage the use of bednets whenever transmission can occur. Communities would benefit from impregnated bednets and other vector control measures being better adapted to their homes, thus reducing the inconvenience of their use.</p

Plant-mediated effects on mosquito capacity to transmit human malaria

The ecological context in which mosquitoes and malaria parasites interact has received little attention, compared to the genetic and molecular aspects of malaria transmission. Plant nectar and fruits are important for the nutritional ecology of malaria vectors, but how the natural diversity of plant-derived sugar sources affects mosquito competence for malaria parasites is unclear. To test this, we infected Anopheles coluzzi, an important African malaria vector, with sympatric field isolates of Plasmodium falciparum, using direct membrane feeding assays. Through a series of experiments, we then examined the effects of sugar meals from Thevetia neriifolia and Barleria lupilina cuttings that included flowers, and fruit from Lannea microcarpa and Mangifera indica on parasite and mosquito traits that are key for determining the intensity of malaria transmission. We found that the source of plant sugar meal differentially affected infection prevalence and intensity, the development duration of the parasites, as well as the survival and fecundity of the vector. These effects are likely the result of complex interactions between toxic secondary metabolites and the nutritional quality of the plant sugar source, as well as of host resource availability and parasite growth. Using an epidemiological model, we show that plant sugar source can be a significant driver of malaria transmission dynamics, with some plant species exhibiting either transmission-reducing or -enhancing activities

Similarity-based Neuro-Fuzzy Networks and Genetic Algorithms in Time Series Models Discovery

This paper presents a hybrid soft computing technique for the study of time varying processes based on a combination of neurofuzzy techniques with evolutionary algorithms, in particular, genetic algorithms . Two problems are simultaneously addressed: the discovery of patterns of dependency in general multivariate dynamic systems (in an optimal or quasi-optimal sense), and the construction of a suitable initial representation for the function expressing the dependencies for the best model found. The patterns of dependency are represented by general autoregresive models (not necessarily linear), relating future values of a target variable with its past values as well as with those of the other observed variables. These patterns of dependencies are explored with genetic algorithm, whereas the functional approximation is constructed with a neurofuzzy heterogeneous network. The particular kind of neurofuzzy network chosen uses a nonclassical neuron model based on similarity in the hidden layer, and a classical neuron model in the output layer. An instance-based training approach allows a rapid construction of a complete network from the multivariate signal set and the dependency pattern under exploration, thus allowing the investigation of many prospective patterns in a short time. The main goal of the technique is the rapid prototyping and characterization of interesting or relevant interdependencies, especially in poorly known complex multivariate processes. The genetic search of the space of possible models (astronomically huge in most practical problems) doesn't guarantee the optimality of the models discovered. However, it provides a set of plausible dependency patterns explaining the interactions taking place, which can be refined later on by using more sophisticated techniques (also more time consuming) as function approximators, to improve the quality of the forecasting operator. Examples with known time series show that the proposed approach gives better results than the classical statistical one.Nous pr\ue9sentons une technique de calcul hybride \uab\ua0souple\ua0\ubb pour l'\ue9tude des processus chronologiques, combinant des techniques neuro-floues et des algorithmes \ue9volutionnaires, notamment des algorithmes g\ue9n\ue9tiques. Deux probl\ue8mes sont abord\ue9s simultan\ue9ment : (1) la d\ue9couverte de motifs de d\ue9pendance dans les syst\ue8mes dynamiques g\ue9n\ue9raux multivari\ue9s (dans un sens optimal ou quasi optimal) et (2) la construction d'une repr\ue9sentation initiale convenable pour la fonction exprimant les d\ue9pendances du meilleur syst\ue8me trouv\ue9. Les motifs de d\ue9pendance sont repr\ue9sent\ue9s par des mod\ue8les autor\ue9gressifs g\ue9n\ue9raux (pas n\ue9cessairement lin\ue9aires) reliant les valeurs ult\ue9rieures d'une variable cible avec ses valeurs ant\ue9rieures et celles d'autres valeurs observ\ue9es. L'algorithme g\ue9n\ue9tique explore ces motifs de d\ue9pendance alors qu'un r\ue9seau neuro-flou h\ue9t\ue9rog\ue8ne construit l'approximation fonctionnelle. Le r\ue9seau neuro-flou choisi comprend dans sa couche cach\ue9e, un mod\ue8le de neurones non classiques bas\ue9s sur la similitude et, dans sa couche de sortie, un mod\ue8le de neurones classiques. L'entra\ueenement bas\ue9 sur les instances permet d'\ue9laborer rapidement un r\ue9seau complet \ue0 partir de l'ensemble des signaux multivari\ue9s et le motif de d\ue9pendance explor\ue9, ce qui permet d'explorer plusieurs motifs possibles dans un temps court. Cette technique a pour objectif principal le prototypage rapide et la caract\ue9risation d'interd\ue9pendances int\ue9ressantes ou appropri\ue9es, notamment pour les processus multivari\ue9s complexes et mal connus. L'exploration g\ue9n\ue9tique de l'univers des mod\ue8les possibles (d'une taille astronomique dans la plupart des cas pratiques) ne garantit pas que les mod\ue8les d\ue9couverts soient optimaux. Toutefois, elle donne un ensemble de motifs de d\ue9pendance plausibles qui expliquent les interactions en cours. Pour am\ue9liorer la qualit\ue9 de l'op\ue9rateur de pr\ue9diction, on pourra raffiner ult\ue9rieurement cet ensemble \ue0 l'aide de techniques plus complexes (mais aussi plus lentes) comme les approximateurs de fonction. Nos calculs sur des fonctions chronologiques connues ont montr\ue9 que l'approche propos\ue9e donnait de meilleurs r\ue9sultats que l'approche statistique classique.NRC publication: Ye

First detection of Leishmania infantum in domestic dogs from Burkina Faso (West Africa)

Background and Objective: Human Visceral Leishmaniasis (HVL) is a systemic neglected tropical diseases and potentially lethal disease caused by infection with protozoan parasites of the Leishmania genus. In the causal, agent of HVL is L. infantum and dogs are a major reservoir host. Visceral leishmaniasis is rarely found in West Africa and no cases have been reported to date in Burkina Faso. The purpose of the current study was to investigate the presence of L. infantum in population of domestic dogs in Bobo-Dioulasso city in Burkina Faso. Materials and Methods: The study was carried out in five districts of the city Bobo-Dioulasso, Burkina Faso. An active survey was conducted in households with dogs in five districts of the city for canine leishmaniasis screening. Epidemiological data and clinical signs were collected for each dog. Venous blood collection and skin lesions biopsies were performed in dogs after informed consent of the owners. The plasma was used for the immunological diagnosis (DiaMed-IT LEISH) and positive samples were confirmed by nested PCR. Results: A total of 85 dogs were included in the study. For the first time, the occurrence of L. infantum in Burkina Faso was confirmed in five domestic dogs presenting symptomatic signs by immunochromatographic tests. Biopsy samples were positive for L. infantum in PCR analysis. Conclusion: The findings indicated that L. infantum is circulating within canine populations in Bobo-Dioulasso. Infected dogs would be the reservoir hosts of this visceralising species. Several priorities for public and veterinary health research have been highlighted by this study

effects of larval stress and parasite infection

full data set of effects of predation stress and infection on larval development, adult size, fecundity, longevity and mosquito susceptibility

Data from: Plant-mediated effects on mosquito capacity to transmit human malaria

The ecological context in which mosquitoes and malaria parasites interact has received little attention, compared to the genetic and molecular aspects of malaria transmission. Plant nectar and fruits are important for the nutritional ecology of malaria vectors, but how the natural diversity of plant-derived sugar sources affects mosquito competence for malaria parasites is unclear. To test this, we infected Anopheles coluzzi, an important African malaria vector, with sympatric field isolates of Plasmodium falciparum, using direct membrane feeding assays. Through a series of experiments, we then examined the effects of sugar meals from Thevetia neriifolia and Barleria lupilina cuttings that included flowers, and fruit from Lannea microcarpa and Mangifera indica on parasite and mosquito traits that are key for determining the intensity of malaria transmission. We found that the source of plant sugar meal differentially affected infection prevalence and intensity, the development duration of the parasites, as well as the survival and fecundity of the vector. These effects are likely the result of complex interactions between toxic secondary metabolites and the nutritional quality of the plant sugar source, as well as of host resource availability and parasite growth. Using an epidemiological model, we show that plant sugar source can be a significant driver of malaria transmission dynamics, with some plant species exhibiting either transmission-reducing or -enhancing activities