Les Schistosomoses au Bénin (épidémiologie et écologie des interactions hôte-parasite)

Ce travail présente une étude épidémiologique et une étude des interactions hôte-parasite sur les schistosomoses au Bénin. Au plan épidémiologique, une synthèse bibliographique de l'état des travaux réalisés sur les schistosomoses dans l'espace de la Communauté Economique des Etats de l'Afrique de l'Ouest (CEDEAO) a été menée. Au Bénin, nos analyses épidémiologiques ont permis de confirmer l'existence de deux espèces de schistosomes humains : S. haematobium et S. mansoni sur les cinq signalées dans l'espace CEDEAO dans lequel le Bénin se situe (S. haematobium, S. mansoni, S. guineensis, S. bovis et S. curassoni). La prévalence générale obtenue pour S. haematobium est de 85% et celle de S. mansoni est de 30%, avec l'existence de foyers de transmission mixtes. Les prospections malacologiques ont révélé la présence au Bénin d'au moins cinq espèces de mollusques potentiellement vectrices : B. forskalii, B. globosus et B. truncatus, vectrices de S. haematobium, B. pfeifferi, vectrice de S. mansoni et I. exustus, mollusque exotique au Bénin, connu comme vecteur de S. indicum, S. spindale et S. nasale en Asie du sud-est. Nous signalons la présence de I. exustus pour la première fois au Bénin où ce mollusque semble être, pour le moment, passif dans la transmission des schistosomoses. Au plan de l'écologie des interactions mollusque-parasite, notre étude a montré que les différentes populations de S. haematobium sont différemment compatibles avec trois des quatre groupes de mollusques Bulinus : le groupe africanus, le groupe forskalii et le groupe reticulatus alors que les différentes populations de S. mansoni sont toutes également compatibles avec B. pfeifferi. L'analyse de six traits d'histoire de vie, période prépatente, prévalence, production cercarienne chez le parasite et croissance, reproduction et survie des mollusques a été abordée avec cinq populations locales de schistosomes dont trois populations de S. haematobium (Doh, Sô-Tchanhoué et Toho-Todougba) et deux populations de S. mansoni (Kpinnou et Toho-Todougba) et a révélé que si les populations de S. haematobium semblent être adaptées à un vecteur local, ce n'est pas le cas chez l'espèce S. mansoni. Au plan de l'écologie des interactions vertébré-parasite, notre étude a révélé l'existence d'un rythme d'émission cercarienne horaire particulier, de type infradien, à la fois chez S. haematobium et chez S. mansoni. L'étude anthropique réalisée au niveau d'un des foyers de transmission (Toho-Todougba) où les deux espèces sont présentes a permis de constater une parfaite synergie entre la chronobiologie cercarienne et la dynamique des activités chez l'Homme : il pourrait s'agir d'une stratégie développée par le parasite pour maintenir ses rendez-vous avec son hôte naturel vertébré.This work presents an epidemiological and an ecological study of schistosomiasis in Benin. A synthesis of the epidemiological knowledge of schistosomiasis in the space of the Economic Community of West Africa States (ECOWAS) was carried out. Furthermore, in Benin, we confirmed the existence of the two human schistosomes : S. haematobium and S. mansoni on the five existing in the ECOWAS space in which Benin is located (S. haematobium, S. mansoni, S. guineensis, S. bovis and S. curassoni). The prevalence obtained for S. haematobium was 85% and that for S. mansoni was 30%, and there was evidence for mixed human infections. We could find in Benin at least five potentially snail vector species : B. forskalii, B. globosus and B. truncatus for S. haematobium, B. pfeifferi for S. mansoni and I. exustus, an exotic snail known to be the snail vector for S. indicum, S. spindale and S. nasale in South-East Asia. I. exustus is recorded for the first time in Benin in this work and no evidence of active transmission was made. The study of the snail-schistosome interactions showed that the different S. haematobium populations were differently compatible with three of the four groups of Bulinus : the africanus group, the forskalii group and the reticulatus group and that the different S. mansoni populations were equally compatible with B. pfeifferi. The six life-history traits, parasite prepatent period, prevalence and cercarial production and snail growth, reproduction and survival were analyzed using five schistosome populations from Benin including three populations of S. haematobium (Doh, Sô-Tchanhoué and Toho-Todougba) and two populations of S. mansoni (Kpinnou and Toho-Todougba) and revealed that if the S. haematobium populations seemed to be adapted to a local vector, this was not the case for the S. mansoni populations. The study of the vertebrate-schistosome interactions revealed the existence of an infradian rhythm in the cercarial emissions of both S. haematobium and S. mansoni. The human behaviour, followed in one of the transmission sites (Toho-Todougba) where both schistosome species are present, was perfectly correlated with the schistosome chronobiology. This was interpreted in terms of adaptative strategy favouring the transmission of the parasite to its human host.PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

Some pathophysiological insights into ovarian infestation by Myxobolus sp. (Myxozoa: Myxosporea) in Clarias gariepinus (Clariids: Silurids) from Bénin (West Africa)

International audienceMature female specimens of the catfish Clarias gariepinus originating from Ouémé River (Benin) were investigated into ovarian myxozoan parasites. Spores of Myxobolus sp. (Myxozoa: Myxosporea) were found encrusted in the whitish color oocytes which present fat dot aspect in the gonads. The pathological investigation by electron microscopy revealed that maturation and multiplication of spores induced lytic action, deformation and dysfunction of the oocyte internal structures. No host inflammatory reaction was observed, while yolk, lipid, mitochondria, and other oocyte components were degenerated inducing empty area in the oocyte and could lead to castration in case of wide infestation. The mean prevalence was 19.79 %. No significant difference was observed within seasonal prevalence (χ2 = 1.771; df = 3; p > 0.05). Though the host length classes ranging from 35 to 39 cm and 40 to 45 cm were more infected, difference was not significant (χ2 = 2.273; df = 4; p > 0.05) within them. The spores are ovoid in shape with two polar capsules which are equal in size, pyriform, and converging in anterior part of spore with four to five polar filament turns. Spore body are (11.47 ± 0.67) × (8.19 ± 0.52) μm length by width while polar capsule size are (4.24 ± 0.25) × (3.07 ± 0.28) μm and located in the first third portion of the spore. The molecular approaches are still running for accurate identification of this parasite

Histopathological and ultrastructural studies of a Henneguya species (Myxozoa: Myxosporea) infesting the intestine of Clarias gariepinus from Benin (West Africa)

International audienceFish culture is the best alternative to fill the gap between natural fish catches and estimated needs of populations in animal protein consumption. In West Africa, this goal required to have suitable fishes for aquaculture which are Clariidae and Tilapia. Clarias gariepinus (Clariidae) fetches a higher price than tilapias as it can be sold alive at the market but a high infestation by Henneguya leads to decrease this commercial value. Those reasons lead us to perform studies on seasonal variations, histopathological aspects and life cycle of Henneguya sp. infecting the intestine of C. gariepinus using light and electron microscope. From November 2011 to December 2012, 339 specimens were collected from Ouémé River (Benin) and examined. An overall prevalence of 7.37 % was recorded for plasmodia of Henneguya sp. Parasite occurrence did not vary significantly between seasons (χ2 = 12.235; df = 3; p > 0.05), nor sexes (χ2 = 2.992; df = 7; p > 0.05) while differences were significant between classes of weight (χ2 = 39.929; df = 5; p < 0.05). The highest prevalence was recorded in host ranging from 300 to 374 g. Histopathological analysis showed that the mass continuous development of the plasmodium produced thickening of the intestine wall and compressed neighboring tissues and destroyed villi and smooth muscle layers. The stages of the parasite development including sporogenesis, capsulogenesis, and valvogenesis were asynchronous. Investigations are still running by molecular approaches in order to identify accurately this species