Regular treatments of praziquantel do not impact on the genetic make-up of Schistosoma mansoni in Northern Senegal.

The Senegal River Basin (SRB) experienced a major epidemic of intestinal schistosomiasis in the early nineties, after the construction of a dam for irrigation purposes. Exceptionally low cure rates following praziquantel (PZQ) treatment at the onset of the epidemic raised concerns about PZQ resistant strains of Schistosoma mansoni, although they could also be attributed to the intense transmission at that time. A field study in the same region more than 15 years later found cure rates for S. mansoni still to be low, whereas Schistosomahaematobium responded well to treatment. We collected S. mansoni miracidia from children at base-line prior to treatment, six months after two PZQ treatments and two years after the start of the study when they had received a total of five PZQ treatments. In total, 434 miracidia from 12 children were successfully genotyped with at least six out of nine DNA microsatellite loci. We found no significant differences in the genetic diversity of, and genetic differentiation between parasite populations before and after repeated treatment, suggesting that PZQ treatment does not have an impact on the neutral evolution of the parasite. This is in stark contrast with a similar study in Tanzania where a significant decrease in genetic diversity was observed in S. mansoni miracidia after a single round of PZQ treatment. We argue that PZQ resistance might play a role in our study area, although rapid re-infection cannot be excluded. It is important to monitor this situation carefully and conduct larger field studies with short-term follow-up after treatment. Since PZQ is the only general schistosomicide available, the possibility of PZQ resistance is of great concern both for disease control and for curative use in clinical practice.

Seasonality in the transmission of schistosomiasis and in populations of its snail intermediate hosts in and around a sugar irrigation scheme at Richard Toll, Senegal.

Irrigation for intensive sugar cultivation started in the early 1980s at Richard Toll, some 100 km from the mouth of the Senegal River. Infections with Schistosoma mansoni were first seen in late 1988. This study records quantitative snail surveys for over 3 years from 1992 at sites representing different habitats in and around the irrigation scheme. Populations of both Biomphalaria pfeifferi (the intermediate host of S. mansoni) and Bulinus spp. (mainly B. truncatus, the local host of S. boris) peaked in late 'spring' or early 'summer', depending on the habitat, and then remained low until the following spring', B. pfeifferi favoured smaller, man-made habitats with most transmission between May and August each year. The less abundant Bulinus spp. favoured larger natural and man-made habitats with most S. bovis transmission between April and July. S. mansoni infections were more, but S. bovis infections were less abundant than other trematodes in their respective snail hosts. Ecological changes in the early 1980s due to sugar irrigation pre-dated similar, more widespread changes in the late 1980s when the completion of dams across the Senegal River prevented seasonal rain fed floods and sea water intrusion. S. mansoni has since spread rapidly around Richard Toll. The incompatibility of the local S. haematobium strains with the dominant bulinid snails has so far prevented an epidemic of urinary schistosomiasis at Richard Toll, but the invasion of similar downstream habitats by susceptible B. globosus is worrying. The principal control measure, chemotherapy, given in the 'winter' would minimise the rate of reinfection. It could be reinforced by judicious mollusciciding within the sugar irrigation scheme but not elsewhere.

Preliminary study of urinary schistosomiasis in a village in the delta of the Senegal river basin, Senegal.

Three years after the first cases of urinary schistosomiasis infection were reported in the village of Mbodiene, Senegal, Schistosoma haematobium eggs were found in 87% of the inhabitants of this village; 30% were heavily infected (> 50 eggs per 10 mL urine). The prevalence of infection was very high in all age groups, but children showed more intense infections. No difference between sexes was found. In the special situation of a very high prevalence, test strips for proteinuria and haematuria are not very useful for the individual diagnosis of S. haematobium infection. Six and 12 weeks after treatment with a single dose of praziquantel (40 mg/kg), S. haematobium eggs were found in 25% and 30% of the treated subjects, respectively. Bulinus globosus was identified as intermediate host, but other snail vectors may also play a role. S. mansoni eggs were found in 1% of the population. Both S. haematobium and S. mansoni are spreading in the delta of the Senegal river.

[Immunodiagnosis of Fasciola gigantica fascioliasis by ELISA technique in Senegal. Preliminary observations in 2 lambs]. / L'immunodiagnostic de la fasciolose à Fasciola gigantica par la technique ELISA au Sénégal. Observations préliminaires chez deux agneaux.

The purpose of this work was to investigate the use of the ELISA test for the diagnosis of fasciolosis (Fasciola gigantica) in sheep, in Senegal, using Fasciola gigantica metabolic excretion-secretion products as antigens. Coprological analysis results were negative until the fourteenth week following infection; using the ELISA test, the first anti-Fasciola gigantica antibodies can be detected as early as the fourth week following infection.

[Epidemiology of intestinal schistosomiasis with Schistosoma mansoni in Richard-Toll (Delta of the Senegal River). Malacological study]. / Epidémiologie de la bilharziose intestinale à Schistosoma mansoni à Richard-Toll (Delta du fleuve Sénégal). Etude malacologique.

A recent outbreak of intestinal schistosomiasis (1989) has been reported in Richard-Toll (Delta of Senegal River) with a global prevalence of 43%. A malacological survey has been carried in order to study, the density of Biomphalaria pfeifferi the intermediate hosts, their distribution and rate of infection, and to identify the transmission sites. Ten districts have been selected. The snails have been collected in the different water points of these localities which are the river, the Taouey marigot, the Taouey channel and the irrigation channels and drains of the CSS (Senegal Sugar Company). A total of 1,210 Biomphalaria have been collected in 45 sites with a variable density of 2 to 150 snails. The overall rate of infestation of snails is 44% but varies according to the districts (9 to 64%). The transmission is acting in all the districts mainly in the Taouey channel (28% of infested snails) the Taouey marigot (38% of infested snails) and particularly in the channels of CSS (47% of infested snails). The situation is alarming and requires urgent action be undertaken to decrease the prevalence and reduce the transmission.

[Resistance to drought of mollusks of the genus Bulinus, vectors of human and animal trematode infections in Senegal. II. Study under natural conditions in the North-Sudan area. Ecology and resistance to drought of Bulinus umbilicatus and B. senegalensis]. / Résistance à la sécheresse de mollusques du genre Bulinus vecteurs de trématodoses humaines et animales au Sénégal. II. Etude dans les conditions naturelles en zone Nord-soudanienne. Ecologie et résistance à la sécheresse de Bulinus umbilicatus et B. senegalensis.

The authors report on the results of a 2-year study on the ecology and resistance to drought of B. umbilicatus and B. senegalensis on 3 temporary ponds in the North-Sudan area (region of Tambacounda, Senegal). The variations in some abiotic factors like the temperature and the pH of water do not seem to have a strong influence on the ecology while rainfall has a great importance on the distribution and the density of molluscs. As a fact, the quantity of water and the drying out period of these ponds depend upon rain factors which rule the existence and the survival of the malacological fauna. In the second part of the rainy season, the population reaches its maximum, i.e., during the reproduction period. Monthly observations show that the relative abundance of B. umbilicatus is higher than that of B. senegalensis. These ponds are dry during 6 to 8 months per year. However the populations of molluscs regenerate regularly, a fact which presupposes a certain ability to resist drought. Some come through this period successfully, but the middle-sized ones (7 to 9.9 mm) resist better than others (70 to 80 per cent of the population). Immediately after the first rains they resume their activity and lay intensively in order to reconstitute the population. B. umbilicatus and B. senegalensis are potential intermediate hosts for human and animal trematode infections, but in the studied region only B. umbilicatus intervenes in the transmission of S. haematobium and S. curassoni which occurs between September and November. Under natural Sahel conditions the epidemiological cycle is short and everything happens within 4 to 6 months with the regeneration and the growth of the population of molluscs, its infestation and the transmission of trematode infections. The ecological behaviour of these molluscs in the North-Sudan region is very important in the epidemiology of human and animal trematode infections and requires a new controlling strategy. The destruction of molluscs is more effective and more economic at the end of the rain season, which is the beginning of the drying of ponds, a period in which they concentrate in the residual water pools.

[Morphology of the teguments of Schistosoma haematobium; comparison with S. curassoni, S. bovis and S. intercalatum]. / Morphologie des téguments de Schistosoma haematobium; comparison avec S. curassoni, S. bovis et S. intercalatum.

Study by SEM of the anterior dorsal teguments of male Schistosoma haematobium from infected rodents. Only paired males, at least hundred days post infection, display a typical morphology. Differentiation from other closely related species obtained experimentally from rodents is possible: bovis: no spines on the tubercles; haematobium: tubercles 10 to 15 microns wide with closely packed spines; curassoni: tubercles over 15 microns wide, with large, closely packed spines; intercalatum: tubercles under 10 microns wide, with scattered spines. It is suggested that the three haematobium genotypes A, B and D are slightly different: A: pointed spines, numerous small additional spines between the tubercles; B: pointed spines, no small additional spines between the tubercles; D: blunt spines. Moreover, the lengths of the prepatent periods in the molluscs of the three S. haematobium genotypes are possibly different: A 72-86 days, B 38-46 days, D 55-58 days. The differentiation of A, B and D is supported by limited data and conclusions on this particular aspect are presented only as a working hypothesis.

[Morphology of the teguments of Schistosoma bovis; variations linked to the vertebrate host; comparison with S. curassoni]. / Morphologie des téguments de Schistosoma bovis; variations selon l'hote vertébré; comparaison avec S. curassoni.

S. E. M. study of the dorsal anterior one third of male Schistosoma bovis and of the anterior ventral border of the gynaecophoric duct. S. bovis was previously described as possessing spineless tubercles. This is so in specimens obtained from experimentally infected rodents, but in cattle, on the contrary, when conditions are favourable, teguments have spiny tubercles. Two morphological types have been observed: the first in Bos taurus from Sardinia, the second in domestic (Bos indicus) and wild (Hippotragus equinus and Damaliscus korrigum) bovids from Senegal, Tchad and Centrafrican Republic.

[Chaetotaxy of Gastrodiscus aegyptiacus cercaria (Trematoda, Paramphistomoidea) a horse parasite]. / Chétotaxie de la cercaire de Gastrodiscus aegyptiacus (Trematoda, Paramphistomoidea) parasite du cheval.

Cercarial chaetotaxy of Gastrodiscus aegyptiacus (Paramphistomoidea), parasite of the Horse, is described. Cercariae were shed by experimentally infected Bulinus forskalii. This description is the first one of a Gastrodiscidae. The cercarial chaetotaxy of the Gastrodiscidae is quite different from those of Paramphistomoidea and Diplodiscidae.

[Survey on Schistosomes of man and livestock in Senegal using specific identification given by chetotaxy of cercaria. I. New arguments for the validation of S. curassoni Brumpt, 1931, parasite of man and domestic Bovidae]. / Enquête sur les schistosomes de l'homme et du bétail au Sénégal, à l'aide des identifictions spécifiques fournies par la chétotaxie des cercaires. I. Nouveaux arguments pour la validation de S. curassoni Brumpt, 1931, parasite de l'homme et des Bovidés domestiques.

Study of Senegal cercariae emitted by naturally infected snails or by snails experimentally infected using eggs from human urine or from sheep liver, and study of the corresponding eggs. The relative position of the dorsal sensillae of cercariae is described by an "AD index" and the ratio length/width of eggs by an "L/l index." At the present time, we have not finished the epidemiological studies, certain experiments are imperfect and the isoenzyme analysis of the corresponding adults is incomplete. Nevertheless information given by the indices AD and L/l agree and lead us to admit the existence of a Schistosome different to mattheei, haematobium and bovis and which, following Brumpt and Gretillat we refer to as Schistosoma curassoni. If one relies on the indices, the study indicates that: a) S. mattheei has not been found in Senegal, b) S. bovis is quite rare, c) S. haematobium apparently exists in pure infections in Casamance and in mixed infections with S. curassoni in man in the north and in the east, d) S. curassoni is apparently the dominant species in domestic ruminants and in man in the north and in the east, e) Bulinus umbilicatus is the principal vector of S. curassoni and S. haematobium.

[Argyrophilic structures of the larval forms of 2 strains of Paramphistomum microbothrium: 1 a parasite of Isidora guernei and Ovis aries, the other a parasite of Isidora truncata and Bos taurus]. / Structures argyrophiles des formes larvaires de deux souches de Paramphistomum microbothrium: l'une parasite d'Isidora gunernei et Ovis aries, l'autre parasite d'Isidora truncata et Bos taurus.

The life cycle of a Paramphistome from North Senegal is completed starting from cercariae shed by naturally infected Isidora guernei: a sheep and then uninfected Isidora guernei were successively infected experimentally. Adults obtained were identifiable as P. phillerouxi or as P. microbothrium. Species determination cannot be made on the basis of argentophilic structures in the miracidium. Morphology of sporocysts and rediae differs from that observed in P. phillerouxi but is undistinguishable from that described in P. microbothrium. Cercarial chaetotaxy differs from that of P. phillerouxi. Mollusc host: Isidora guernei belongs to the same genus as Isidora truncata and I. alluaudi, reported hosts to P. microbothrium. Therefore the material is provisionally identified as P. microbothrium. To confirm this, a strain of P. microbothrium from naturally infected Bos taurus in Egypt was studied. Miracidia were used to experimentally infect Isidora truncata; cercariae obtained were identical to those previously described for this species from I. truncata and I. alluaudi. Cercarial chaetotaxy was not significantly different from that of material from North Senegal. They represent therefore two strains of Paramphistomum microbothrium.

[Superficial argentophilic structures of miracidium and cercaria of Paramphistomum phillerouxi Dinnik, 1961 (Trematoda, Paramphistomidae) (author's transl)]. / Disposition des organites argyrophiles superficiels du miracidium et de la cercaire de Paramphistomum phillerousi Dinnik, 1961 (Trematoda, Paramphistomidae).

Superficial argentophilic structures of the miracidium and cercaria of Paramphistomum phillerouxi Dinnik, 1961, are descrifed in detail. Concerning the miracidium they are similar to those of the miracidia of some species belonging to the genus. On the other hand the chaetotaxy of the cercaria is different from that of the cercaria of P. togolense (Alberet et coll., 1978) and therefore this appears to constitute a good criterium for the taxonomy of this group.

[Additional data on superficial argentophilic structures of the miracidium and cercaria of Fasciola gigantica (Cobbold, 1855) (Trematoda:Fasciolidae) and on the epidemiology of this parasite]. / Données complémentaires sur les organites argyrophiles superficiels du miracidium et de la cercaire de Fasciola gigantica (Cobbold, 1855) (Trematoda : Fasciolidae) et sur l'épidémiologie de ce parasite.

The life cycle of a senegalese strain of Fasciola gigantica was carried out in France from adults recovered in the liver of naturally infected cattle (Bos taurus). Laboratory-reared Lymnaea natalensis experimentally infected shed numerous cercariae. Metacercariae were used for successful infection of sheep. In the miracidium, variations are observed in the disposition of the medio-ventral epithelial cell of the second tier. The distribution of the superficial argentophilic structures is similar to that of the miracidium of F. hepatica. The chaetotaxy of the cercaria is very closely related to that of the cercaria of a strain of F. gigantica from Madagascar shed by Lymnaea hovarum but it differs clearly from that of the cercaria of F. hepatica. The encystment of a great number of cercariae (25 %) on the surface of water suggests that this is an important factor in the extension of the foci of contamination, and therefore increases greatly the risks of infection not only for animal but also for man. It is possible that human fascioliasis caused by F. gigantica is a disease, the importance of which is under-estimated.