Initiation

La compréhension de l'épidémiologie d'une maladie infectieuse ou parasitaire passe par une connaissance minimale du fonctionnement des populations vivantes concernées. Ainsi, pour remédier à la difficulté d'obtenir des observations directes sur la biologie des populations naturelles, notamment dans les pays du Sud, l'utilisation de marqueurs génétiques permet d'avoir accès, à travers des méthodes indirectes, à des informations clés sur la biologie des agents pathogènes et de leurs vecteurs : écologie, mode de reproduction, déplacements, taille des populations, etc. Un outil précieux dans le domaine de la santé, où l'analyse de la variation spatio-temporelle des marqueurs génétiques peut ainsi être utilisée pour caractériser la dynamique des populations de parasites et de leurs vecteurs, pour connaître l'évolution d'une maladie infectieuse ou parasitaire, évaluer les risques d'invasions ou d'épidémie, le potentiel de diffusion de gènes résistants, anticiper les stratégies de lutte… Ce manuel didactique présente les principales méthodes de la génétique des populations naturelles et les modèles de base utilisés pour les inférences, avec des cas concrets d'applications à destination des étudiants et personnels de santé. Plusieurs jeux de données sont analysés pas à pas dans un CD-ROM qui accompagne l'ouvrage

Decrease in survival and fecundity of Glossina palpalis gambiensis vanderplank 1949 (Diptera : Glossinidae) fed on cattle treated with single doses of ivermectin

Background: Human and Animal Trypanosomes are major problems for the socio-economic growth of developing countries like Burkina Faso. Ivermectin is currently used to treat humans in mass drug administration programs in Africa, and is also commonly used for veterinary purposes. In this study, we tested the effect of ivermectin injected into cattle on the survival and fecundity of Glossina palpalis gambiensis, the main vector of human and animal trypanosomes in West Africa. Methods: Three cows (local zebu*baoule crossbreds) were used, and received either no ivermectin (for the control), or ivermectin at therapeutic dose (0.2 mg/kg) and 10 times the therapeutic dose (2 mg/kg) respectively. G. palpalis gambiensis were fed on the cattle for their first bloodmeal, and then either on cattle or on membrane for subsequent meals. Results: Our results showed that survival of Glossina palpalis gambiensis was significantly decreased when they were fed on cattle treated with ivermectin. This decrease in survival ranged from 21% to 83.7% for the therapeutic dose (0.2 mg/kg), up to 8 days after treatment. The effects of a dose of 2 mg/kg were higher with a 78.3% to 93.9% decrease in survival, until 14 days after injection. The therapeutic dose of ivermectin also decreased fecundity, and delayed the first larviposition, but there was no significant effect on hatching rate. Conclusion: Ivermectin injected into cattle may constitute an additional potential tool for the control of Glossina palpalis gambiensis and possibly other vector species. Further studies will be needed to assess its effect on trypanosome transmission, and to define more precisely the adequate dose to be used for control purposes

Population genetics of Glossina palpalis palpalis from central African sleeping sickness foci

<p>Abstract</p> <p>Background</p> <p><it>Glossina palpalis palpalis </it>(Diptera: Glossinidae) is widespread in west Africa, and is the main vector of sleeping sickness in Cameroon as well as in the Bas Congo Province of the Democratic Republic of Congo. However, little is known on the structure of its populations. We investigated <it>G. p. palpalis </it>population genetic structure in five sleeping sickness foci (four in Cameroon, one in Democratic Republic of Congo) using eight microsatellite DNA markers.</p> <p>Results</p> <p>A strong isolation by distance explains most of the population structure observed in our sampling sites of Cameroon and DRC. The populations here are composed of panmictic subpopulations occupying fairly wide zones with a very strong isolation by distance. Effective population sizes are probably between 20 and 300 individuals and if we assume densities between 120 and 2000 individuals per km², dispersal distance between reproducing adults and their parents extends between 60 and 300 meters.</p> <p>Conclusions</p> <p>This first investigation of population genetic structure of <it>G. p. palpalis </it>in Central Africa has evidenced random mating subpopulations over fairly large areas and is thus at variance with that found in West African populations of <it>G. p. palpalis</it>. This study brings new information on the isolation by distance at a macrogeographic scale which in turn brings useful information on how to organise regional tsetse control. Future investigations should be directed at temporal sampling to have more accurate measures of demographic parameters in order to help vector control decision.</p

Population genetics and reproductive strategies of african trypanosomes : revisiting available published data

Trypanosomatidae are a dangerous family of Euglenobionta parasites that threaten the health and economy of millions of people around the world. More precisely describing the population biology and reproductive mode of such pests is not only a matter of pure science, but can also be useful for understanding parasite adaptation, as well as how parasitism, specialization (parasite specificity), and complex life cycles evolve over time. Studying this parasite&#8217;s reproductive strategies and population structure can also contribute key information to the understanding of the epidemiology of associated diseases; it can also provide clues for elaborating control programs and predicting the probability of success for control campaigns (such as vaccines and drug therapies), along with emergence or re-emergence risks. Population genetics tools, if appropriately used, can provide precise and useful information in these investigations. In this paper, we revisit recent data collected during population genetics surveys of different Trypanosoma species in sub-Saharan Africa. Reproductive modes and population structure depend not only on the taxon but also on the geographical location and data quality (absence or presence of DNA amplification failures). We conclude on issues regarding future directions of research, in particular vis-à-vis genotyping and sampling strategies, which are still relevant yet, too often, neglected issues

Epidemiology of sleeping sickness in Boffa (Guinea) : where are the trypanosomes ?

Human African Trypanosomiasis (HAT) in West Africa is a lethal, neglected disease caused by Trypanosoma brucei gambiense transmitted by the tsetse Glossina palpalis gambiensis. Although the littoral part of Guinea with its typical mangrove habitat is the most prevalent area in West Africa, very few data are available on the epidemiology of the disease in such biotopes. As part of a HAT elimination project in Guinea, we carried a cross-sectional study of the distribution and abundance of people, livestock, tsetse and trypanosomes in the focus of Boffa. An exhaustive census of the human population was done, together with spatial mapping of the area. Entomological data were collected, a human medical survey was organized together with a survey in domestic animals. In total, 45 HAT cases were detected out of 14445 people who attended the survey, these latter representing 50.9% of the total population. Potential additional carriers of T. b. gambiense were also identified by the trypanolysis test (14 human subjects and two domestic animals). No trypanosome pathogenic to animals were found, neither in the 874 tsetse dissected nor in the 300 domestic animals sampled. High densities of tsetse were found in places frequented by humans, such as pirogue jetties, narrow mangrove channels and watering points. The prevalence of T. b. gambiense in humans, combined to low attendance of the population at risk to medical surveys, and to an additional proportion of human and animal carriers of T. b. gambiense who are not treated, highlights the limits of strategies targeting HAT patients only. In order to stop T. b. gambiense transmission, vector control should be added to the current strategy of case detection and treatment. Such an integrated strategy will combine medical surveillance to find and treat cases, and vector control activities to protect people from the infective bites of tsetse

MultiTest V.1.2, a program to binomially combine independent tests and performance comparison with other related methods on proportional data

<p>Abstract</p> <p>Background</p> <p>Combining multiple independent tests, when all test the same hypothesis and in the same direction, has been the subject of several approaches. Besides the inappropriate (in this case) Bonferroni procedure, the Fisher's method has been widely used, in particular in population genetics. This last method has nevertheless been challenged by the SGM (symmetry around the geometric mean) and Stouffer's <it>Z</it>-transformed methods that are less sensitive to asymmetry and deviations from uniformity of the distribution of the partial <it>P</it>-values. Performances of these different procedures were never compared on proportional data such as those currently used in population genetics.</p> <p>Results</p> <p>We present new software that implements a more recent method, the generalised binomial procedure, which tests for the deviation of the observed proportion of <it>P</it>-values lying under a chosen threshold from the expected proportion of such <it>P</it>-values under the null hypothesis. The respective performances of all available procedures were evaluated using simulated data under the null hypothesis with standard <it>P</it>-values distribution (differentiation tests). All procedures more or less behaved consistently with ~5% significant tests at <it>α </it>= 0.05. Then, linkage disequilibrium tests with increasing signal strength (rate of clonal reproduction), known to generate highly non-standard <it>P</it>-value distributions are undertaken and finally real population genetics data are analysed. In these cases, all procedures appear, more or less equally, very conservative, though SGM seems slightly more conservative.</p> <p>Conclusion</p> <p>Based on our results and those discussed in the literature we conclude that the generalised binomial and Stouffer's <it>Z </it>procedures should be preferred and <it>Z </it>when the number of tests is very small. The more conservative SGM might still be appropriate for meta-analyses when a strong publication bias in favour of significant results is expected to inflate type 2 error.</p