Impact of seasonal malaria chemoprevention in children aged 3 to 59 months in the Kangaba and Kolokani health districts between 2013 and 2015

INTRODUCTION

Malaria is a public health problem in Mali. Seasonal chemo prevention (SCP) is of particular importance, hence its introduction by the WHO since 2012 in children aged 3 to 59 months from the start of the transmission season. This study aims to demonstrate the impact of SCP on malaria in the health districts of Kangaba and Kolokani.

MATERIALS AND METHODS

Our retrospective study was carried out from 2013 to 2015 in the health districts of Kangaba and Kolokani using the databases of the NGO AMCP / ALIMA. Data from 2014 and 2015 were compared to data from 2013.

RESULTS

The number of malaria cases in children under 5year in the area covered by the SCP shows a considerable decrease in Kangaba of 52% in 2014 and 49% in 2015, compared to the reference period being the year 2013. In Kolokani the decrease is 57% in 2014 and 40% in 2015 compared to the year 2013. Compared to deaths, a decrease of 50.5% was recorded in 2014 and 60.4% in 2015 compared to the year 2013, i.e. 51 and 61 fewer deaths compared to 2013, respectively, in health facilities.

CONCLUSION

The SCP had made it possible to reduce significant mortality and malaria morbidity in the two health districts of Kangaba and Kolokani.

Chromosomal inversions and ecotypic differentiation in Anopheles gambiae: the perspective from whole-genome sequencing

The molecular mechanisms and genetic architecture that facilitate adaptive radiation of lineages remain elusive. Polymorphic chromosomal inversions, due to their recombination-reducing effect, are proposed instruments of ecotypic differentiation. Here, we study an ecologically diversifying lineage of Anopheles gambiae, known as the Bamako chromosomal form based on its unique complement of three chromosomal inversions, to explore the impact of these inversions on ecotypic differentiation. We used pooled and individual genome sequencing of Bamako, typical (non-Bamako) An. gambiae and the sister species Anopheles coluzzii to investigate evolutionary relationships and genomewide patterns of nucleotide diversity and differentiation among lineages. Despite extensive shared polymorphism and limited differentiation from the other taxa, Bamako clusters apart from the other taxa, and forms a maximally supported clade in neighbour-joining trees based on whole-genome data (including inversions) or solely on collinear regions. Nevertheless, F_ST outlier analysis reveals that the majority of differentiated regions between Bamako and typical An. gambiae are located inside chromosomal inversions, consistent with their role in the ecological isolation of Bamako. Exceptionally differentiated genomic regions were enriched for genes implicated in nervous system development and signalling. Candidate genes associated with a selective sweep unique to Bamako contain substitutions not observed in sympatric samples of the other taxa, and several insecticide resistance gene alleles shared between Bamako and other taxa segregate at sharply different frequencies in these samples. Bamako represents a useful window into the initial stages of ecological and genomic differentiation from sympatric populations in this important group of malaria vectors.

Diversity of Sand Flies (Diptera: Psychodidae: Phlebotominae) in Two Different Eco-Climatic and Endemic Zones of Cutaneous Leishmaniasis in Mali, West Africa

Being the only established vectors of the protozoan parasites of the genus Leishmania, sand flies have become very important in all countries where leishmaniasis exists. To better understand the sand fly fauna, a taxonomic inventory study was carried out between January and March 2012 in Soudan savannah (Boundioba, Sikasso) and Sahelian (Tieneguebougou, Koulikoro) areas of Mali. CDC light traps were used to collect the sand flies. Collected sand flies specimens were cleaned with lacto-phenol and examined under a light microscope for species identification. In total, 14 species belonging to the genera Phlebotomus and Sergentomyia were identified. The genus Sergentomyia constituted 98.05% of collected sand flies versus 1.95% for the genus Phlebotomus. The most abundant species were Sergentomyia dubia Parrot, Mornet, & Cadenat, Sergentomyia shwetzi, Sergentomyia clydei Sinton, and Sergentomyia antennata Newstead. In Boundioba, the genus Phlebotomus was represented by two species (Phlebotomus duboscqi Neveu-Lemaire and Phlebotomus rodhaini Parrot), whereas only one species, Ph. duboscqi, was captured in Tieneguebougou. For the first time, three new species, Sergentomyia madagascariensis, Sergentomyia congolensis, and Sergentomyia dureni, were identified in Mali. More investigations are needed for a better entomological assessment of the transmission of cutaneous leishmaniasis in the different eco-climatic zones of Mali.

No evidence for positive selection at two potential targets for malaria transmission-blocking vaccines in Anopheles gambiae s.s

Human malaria causes nearly a million deaths in sub-Saharan Africa each year. The evolution of drug-resistance in the parasite and insecticide resistance in the mosquito vector has complicated control measures and made the need for new control strategies more urgent. Anopheles gambiae s.s. is one of the primary vectors of human malaria in Africa, and parasite-transmission-blocking vaccines targeting Anopheles proteins have been proposed as a possible strategy to control the spread of the disease. However, the success of these hypothetical technologies would depend on the successful ability to broadly target mosquito populations that may be genetically heterogeneous. Understanding the evolutionary pressures shaping genetic variation among candidate target molecules offers a first step towards evaluating the prospects of successfully deploying such technologies. We studied the population genetics of genes encoding two candidate target proteins, the salivary gland protein saglin and the basal lamina structural protein laminin, in wild populations of the M and S molecular forms of A. gambiae in Mali. Through analysis of intraspecific genetic variation and interspecific comparisons, we found no evidence of positive natural selection at the genes encoding these proteins. On the contrary, we found evidence for particularly strong purifying selection at the laminin gene. These results provide insight into the patterns of genetic diversity of saglin and laminin, and we discuss these findings in relation to the potential development of these molecules as vaccine targets.

Attraction of Stomoxys sp. to various fruits and flowers in Mali

The attraction of three Stomoxys species to 26 fruits and 26 flowers of different plant species was investigated in two different sites in Mali during 2008. Stomoxys niger bilineatus Grunberg (Diptera: Muscidae) was attracted to a wider spectrum of species, significantly attracted by four fruits and eight flowers compared with control traps, whereas S. sitiens Rondani (Diptera: Muscidae) was attracted to six fruits and seven flowers of different plants, and S. calcitrans L. (Diptera: Muscidae) was only attracted to one fruit and three flowers. Cold anthrone assays showed a significantly higher prevalence of sugar feeding amongst all three species at the lagoon site than at the site near Mopti. The rhythm of activity study shows temporally separated blood- and sugar-feeding periods for S. niger bilineatus and S. sitiens, but not for S. calcitrans. A comparison between blood and sugar feeding throughout the day shows that sugar feeding activity is as frequent as blood feeding activity. Because not much is known about the preferred sugar sources for Stomoxys species in their natural habitats, the present study provides valuable information regarding the attraction capability of several plants with possible future implication for Stomoxys control strategies.

The spatial distribution of Anopheles gambiae sensu stricto and An. arabiensis (Diptera: Culicidae) in Mali

Variations in the biology and ecology and the high level of genetic polymorphism of malaria vectors in Africa highlight the value of mapping their spatial distribution to enhance successful implementation of integrated vector management. The objective of this study was to collate data on the relative frequencies of Anopheles gambiae s.s. and An. arabiensis mosquitoes in Mali, to assess their association with climate and environmental covariates, and to produce maps of their spatial distribution. Bayesian geostatistical logistic regression models were fitted to identify environmental determinants of the relative frequencies of An. gambiae s.s. and An. arabiensis species and to produce smooth maps of their geographical distribution. The frequency of An. arabiensis was positively associated with the normalized difference vegetation index, the soil water storage index, the maximum temperature and the distance to water bodies. It was negatively associated with the minimum temperature and rainfall. The predicted map suggests that, in West Africa, An. arabiensis is concentrated in the drier savannah areas, while An. gambiae s.s. prefers the southern savannah and land along the rivers, particularly the inner delta of Niger. Because the insecticide knockdown resistance (kdr) gene is reported only in An. gambiae s.s. in Mali, the maps provide valuable information for vector control. They may also be useful for planning future implementation of malaria control by genetically manipulated mosquitoes.

Establishing an insect disease vector functional genomics training center in Africa

The genome sequences for many insects vector of human diseases are now available and promise the development of a set of new, powerful tools that can be used to develop innovative approaches to control these diseases. The African continent, which is the most severely affected by vector borne diseases, lacks adequate infrastructures and personal resources required for rational use of genomic information. To fill this gap, the African Center for Training in Functional Genomics of Insect vectors of Human Disease (AFRO VECTGEN) was initiated by WHO/TDR and the Department of Medical Entomology and Vector Ecology (DMEVE) of the Malaria Research and Training Center (MRTC) in Mali. The aim of the AFRO VECTGEN program is to train young scientists in functional genomics who will ultimately use genome sequence data for research on insect vector of human disease. The program could trigger collaborative research and will benefit from an existing vector biology network in Mali, which was built around research grants funded by the National Institutes of Health, USA and WHO/TDR.

Patterns of irrigated rice growth and malaria vector breeding in Mali using multi-temporal ERS-2 synthetic aperture radar

We explored the use of the European Remote Sensing Satellite 2 Synthetic Aperture Radar (ERS-2 SAR) to trace the development of rice plants in an irrigated area near Niono, Mali and relate that to the density of anopheline mosquitoes, especially An. gambiae. This is important because such mosquitoes are the major vectors of malaria in sub-Saharan Africa, and their development is often coupled to the cycle of rice development. We collected larval samples, mapped rice fields using GPS and recorded rice growth stages simultaneously with eight ERS-2 SAR acquisitions. We were able to discriminate among rice growth stages using ERS-2 SAR backscatter data, especially among the early stages of rice growth, which produce the largest numbers of larvae. We could also distinguish between basins that produced high and low numbers of anophelines within the stage of peak production. After the peak, larval numbers dropped as rice plants grew taller and thicker, reducing the amount of light reaching the water surface. ERS-2 SAR backscatter increased concomitantly. Our data support the belief that ERS-2 SAR data may be helpful for mapping the spatial patterns of rice growth, distinguishing different agricultural practices, and monitoring the abundance of vectors in nearby villages.

Microsatellite DNA and isozyme variability in a west African population of Anopheles gambiae

Microsatellites are defined as tracts of tandemly repeated short DNA sequences. Polymorphisms in this class of DNA are currently being used to generate a genetic map of the mosquito Anopheles gambiae. In the present study we explore the potential of microsatellites as a tool for studying the genetic structure of natural populations of this malaria vector. Genetic polymorphism at twenty enzyme coding gene loci and eleven microsatellite DNA loci was surveyed in a population of An. gambiae from Mali, West Africa. All of the microsatellite loci surveyed were polymorphic, as compared to 40% of the isozyme loci. The mean heterozygosity for the isozyme loci was only 0.097 (+/- 0.0035), but for the microsatellite loci it was 0.732 (+/- 0.060). The pattern of variability was very different between isozymes and microsatellites. Typically, at an isozyme locus a single allele occurred at a frequency > or = 0.75, whereas at microsatellite loci the most common allele had a frequency < 0.50. We conclude that microsatellites provide a rich source of genetic polymorphisms for the study of the population genetics of An. gambiae and are in many ways superior to isozymes for this purpose. We discuss the potential for utilizing genetically mapped microsatellite loci to explore the effect of chromosomal inversions on the distribution of genetic polymorphisms in An. gambiae.