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INTRODUCTION: la schistosomiase, deuxieme endemie parasitaire mondiale, est une parasitose due aux trematodes du genre Schistosoma. Nos objectifs etaient d’evaluer les prevalences des differentes especes de schistosomes (Schistosoma mansoni, haematobium, et intercalatum) chez les ecoliers, et d’identifier les facteurs de risques, les signes cliniques de la schistosomiase, et les mollusques hotes intermediaires des schistosomiases dans les eaux stagnantes. METHODES: l’etude etait transversale et s’est deroulee sur 3 mois. Elle consistait en l’enregistrement des donnees sociodemographiques et cliniques, le prelevement des echantillons de selles et d’urines, la recherche des mollusques et le traitement des ecoliers positifs a d’autres helminthes. Les examens de laboratoire se sont deroules a l’Institut de recherches Medicales et d’etudes des Plantes Medicinales a Yaounde ou on examinait les echantillons de selles et d’urine par les methodes de KATO KATZ et de centrifugation respectivement, et un malacologiste determinait l’espece des mollusques. RESULTATS: au total, 400 eleves âges entre 8-16 ans, soit 223 (55.7%) filles et 177 (44.3%) garcons repartis dans 4 ecoles primaires ont participe a l’etude. L’enquete sociale a revele que 154 ecoliers sur 400 (soit 38.5%) etaient en contact avec les eaux de riviere au moins une fois par semaine, dont 58% aux environs de midi. Tous les eleves avaient au moins un signe de schistosomiase bien que non specifique predomine par des douleurs abdominales a 72% (n= 288 sur 400). Sur le plan biologique aucun œuf de schistosomiase n’a ete mis en evidence. Le taux d’emission de cercaire etait negatif chez les 100 especes aquatiques retrouvees. CONCLUSION: l’aire de sante de Santchou n’est pas un foyer actif de schistosomiase, mais reste une zone a risque du fait de la riziculture et de la presence des eaux stagnantes. L’intensification des campagnes d’education sanitaire dans la population permettrait de retarder la survenue de cette parasitose dans la localite.

Studies with animal models have suggested the possibility of interactions between parasites during concurrent infections and have raised the question of a similar phenomenon in humans. The present survey was undertaken to assess the impact of urinary schistosomiasis on the susceptibility of children to malaria. It was carried out in Senegal between September 2001 and March 2002 among 523 children 3-15 years of age. We tested the association between Plasmodium falciparum densities and the load of Schistosoma haematobium egg excretion using a linear mixed model because data were not independent. After controlling for age, sex, and season, we showed that children lightly infected with S. haematobium (1-9 eggs/10 mL of urine) had lower P. falciparum densities than those not infected (beta = -0.34, 95% confidence interval = -0.85, -0.10), suggesting a negative interaction between both parasites.

The importance of the increase in irrigated land on the perimeters of the Middle and Upper Valleys of the Senegal River basin, on the prevalence and intensity of urinary schistosomiasis, was investigated. Surveys were conducted, in May-June 1997, to determine the prevalence and intensity of Schistosoma haematobium infection among 1445 children aged 7-14 years: 1011 in 10 villages near Matam, and 434 in four villages near Bakel. Macrohaematuria was present in seven of the study villages (four near Matan and three near Bakel), whereas microhaematuria was present in all the villages, with prevalences of 10%-73%. A second survey, conducted, in June 1999, on 755 children from nine of the study villages near Matam, demonstrated significant increases in the prevalences of both micro- and macro-haematuria in three of the villages, all of which were adjacent to the Senegal River and practising irrigated agriculture. None of the other study villages re-surveyed was irrigating any of its agricultural land. A longitudinal survey was also carried out, between May 1997 and November 1998, on about 10% of the population (2272 subjects) of Nguidjilone, north of Matam; selective treatment with praziquantel (40 mg/kg) was given in May 1997, and mass treatment in May 1998. The data analysed were those relating to the 125 individuals who provided samples at each survey. Very severe infections (> 1000 eggs/10 ml urine) were seen in five subjects in May 1997. One year later (i.e. 1 year after the selective treatment), the prevalence of urinary schistosomiasis had increased in every age-group. Although prevalence had decreased slightly by November 1998 (6 months after the mass treatment), the intensity of the infections seen had increased in every age-group. At the end of the dry season (May-June 1997), Bulinus truncalus infected with schistosome cercariae were recovered from the Senegal River. However, immediately after the next rainy season (November 1997), no snails were found at any collection site on the river.

A cluster sample survey was conducted in 1998 in 30 schools to assess the effect of the growth of Niamey during the last decade on a urinary schistosomiasis urban focus described in 1989. Two thousand and forty-two children (11.0 + 0.1 years old) had a urine filtration rest and answered a behavioural questionnaire. Snail populations of the sites used by schoolchildren were followed up in 1999. The global prevalence was 15.7% in 1998, as opposed to 23.7% in 1989. The prevalence was very low in schools far from the river and higher in those along the Niger banks, particularly in villages on the periphery of the urban area. Geographical factors were more important than socio-economic ones in explaining the distribution of the disease. Only 46% of the children in Niamey reported water contact ; mainly in the river, rarely in pools and the canal. The infection risk was low in pools (RR = 1.6), high in the river (RR = 3.5) and very high in the canal (RR = 12.5). Malacological studies confirmed the location of transmission sites obtained through parasitological studies and the questionnaire. Sixty-one per cent of the children travelled outside Niamey to the hyperendemic surrounding areas. However, these movements did not increase their infection level. The results are discussed in relation to water contact behaviour and #Schistosoma haematobium$ transmission features. (Résumé d'auteur)

Snail-infection experiments were carried out with a number of different species and populations of #Bulinus$ and isolates of #Schistosoma haematobium$. The parasites came from six localities of the Senegal River basin (SRB), in the Lower Valley (Mbodiene), Middle Valley (Podoe, Diatar, Nguidjilone) and Upper Valley (Aroundou and Galladé). Isolates of #S. haematobium$ from the Middle and Upper Valleys all showed some compatibility with laboratory-bred #B. truncatus$ from Mali, but none of these isolates was compatible with laboratory-bred #B. truncatus$ originating from Senegal. #Schistosoma haematobium$ from Diatar (Middle Valley) was compatible with #B. senegalensis$, whereas #S. haematobium$ from Mbodiene (Lower Valley), which is naturally tranmitted by #B. globosus$, was compatible with #B. senegalensis$ and #B. truncatus$. These data demonstrate that different isolates of #S. haematobium$ from different regions of the SRB exhibit distinct intermediate-host specificities, which in turn will have an effect on the epidemiology of the disease, including the periods of transmission. It is apparent that, in addition to #B. senegalensis$ and #B. globosus$, #B. truncaus$, the most widespread bulinid snail in the SRB, may be playing a role in the epidemiology of urinary schistosomiasis. This conclusion has obvious implications for the future spread of urinary schistosomiasis in the SRB. Chemical and physical measurements from assorted habitats along the SRB, including pH, temperature, salinity, conductivity, and resistivity, are also reported. (Résumé d'auteur)

Patas monkeys were twice immunized with a #Schistosoma haematobium$-derived recombinant glutathione S-transferase (Sh28GST) then challenged with an homologous calibrated challenge. BCG and Freund's Complete Adjuvant (FCA) were used as adjuvants in two distinct protocols. Specific IgC and IgA antibody responses were intense and homogeneous in the animals receiving Sh28GST in the presence of FCA, whereas BCG could only induce moderate and heterogeneous antibody titres. No significant effect on worm burdens was evidenced 36 weeks post-infection in either group of Sh28GST-immunized animals compared to their matched controls receiving an irrelevant protein. Although not significant, 50% reductions in the numbers of eggs located in all tissues (FCA group) and in the urogenital system (BCG group) were noted. Moreover, the total number of excreted eggs was dramatically diminished by 60% and 77% in the BCG and FCA groups, respectively. These reductions reached 75% and 80% in the urines of vaccinated monkeys. Bladder pathology was also reduced in the animals displaying the lowest urinary egg excretions. There was no clear positive or negative correlate between antibody responses and individual levels of protection. Taken as a whole, our results show that Sh28GST was capable of significantly reducing #S. haematobium$ worm fecundity in experimentally infected primates. Although FCA induced higher levels of protection, the efficacy of BCG as an adjuvant appeared sufficient to justify consideration of the future application of this new formulation as a vaccine against human urogenital schistosomosis. (Résumé d'auteur)

The effect of age, previous intensity of infection, and exposure on reinfection with Schistosoma haematobium after treatment was studied in a cohort of 468 subjects six years of age and over living in an irrigation scheme area in Mali. Prevalence and intensity of S. haematobium infection were measured each year between 1989 and 1991, but the reinfection study period was restricted to the last year of the follow-up. Observations were made at the principal water contact sites where the number of Bulinus truncatus shedding furcocercous cercariae was recorded. A cumulative index of exposure taking into account time, duration and type of contact, and malacologic data was calculated for each subject. Univariate analysis showed that the reinfection risk decreased with age and increased with exposure and pretreatment intensity. These results were confirmed by fitting a logistic model that showed that this risk was seven times lower among those 15 years of age and older than among the 6–14-year-old children, while linear trends with exposure to infection and pretreatment intensity were significant. This study supports the concept of an age-acquired resistance to reinfection and is in favor of a predisposition to infection that raises the question of a genetic factor controlling susceptibility/resistance to S. haematobium infection.

The host-parasite relationships of a Schistosoma haematobium isolate, originating from Niger, and the white mouse are described. Swiss OF1 albino mice were exposed individually to 200 cercariae and worms were recovered 9, 12, 16 and 20 weeks post infection. The mean worm returns ranged between 10·54 and 13·5% and did not alter significantly between 9 and 20 weeks post infection. The sex ratio of worms was always in favour of males; from 7·9:1 at 9 weeks after infection it decreased regularly to 3·28:1 at 20 weeks. Male worms reached a mean length of 8·72 mm at 20 weeks. From the 12th week post infection, a high number of eggs was found in the liver and gut. At 20 weeks, eggs were also found in the bladder. Viable eggs and infective miracidia were obtained. The infection of Bulinus truncatus from Niger succeeded with a mean rate of 61% after the first passage through mice. The isolate of S. haematobium was maintained in the laboratory during 3 successive passages through mice. These entirely new results are very probably linked to genetic characteristics peculiar to the S. haematobium populations from Niger.

The relationship between iron status and degree of infection by Schistosoma haematobium was studied in 174 schoolchildren from Niger in an area endemic for urinary schistosomiasis. Iron deficiency was defined by a combination of three reliable indicators: a low serum ferritin level combined with a low transferrin saturation, a high erythrocyte protoporphyrin level, or both. Hematuria and proteinuria were found in 76.4% and 79.9% of the children, respectively, while 95.4% excreted eggs (geometric mean egg count of 31.5 eggs per 10 ml of urine). Anemia was observed in 59.7% of the subjects. The prevalence of iron deficiency was 47.1%. Anemia was associated with iron deficiency in 57.7% of the cases. The hemoglobin level and transferrin saturation decreased significantly when the degree of hematuria increased, while prevalence of anemia and prevalence of iron deficiency increased significantly. The hemoglobin level and the hematocrit were negatively correlated with egg count, while prevalence of anemia increased with increasing egg count. This inverse relationship between degree of infection by S. haematobium and iron status shows a deleterious consequence of urinary schistosomiasis on nutrition and hematopoietic status, which should be considered in the design of nutrition intervention programs.The relationship between iron status and degree of infection by Schistosoma haematobium was examined in 174 schoolchildren from Niger in an area endemic for urinary schistosomiasis. Iron deficiency was defined by a combination of 3 reliable indicators: a low serum ferritin level combined with a low transferrin saturation, a high erythrocyte protoporphyrin level, or both. Hematuria and proteinuria were seen in 76.4% and 79.9% of the children, respectively, while 95.4% excreted eggs (geometric mean egg count of 31.5 eggs/10 ml of urine). Anemia was seen in 59.7% of the subjects. The prevalence of iron deficiency was 47.1%. Anemia was associated with iron deficiency in 57.7% of the cases. Hemoglobin level and transferrin saturation decreased significantly when the degree of hematuria increased, while prevalence of anemia and iron deficiency increased significantly. The hemoglobin level and hematocrit were negatively correlated with egg count, while anemia prevalence increased with increasing egg count. This inverse relationship between degree of infection by s. haematobium and iron status shows a deleterious consequence of urinary schistosomiasis on nutrition and hematopoietic status, which should be considered in the design of nutrition intervention programs.

Resume Au cours d'un essai comparatif de traitement de la schistosomose urinaire avec le praziquantel (30 et 40 mg/kg en une prise) et l'oltipraz (35 mg/kg en deux prises) les auteurs ont traite 103 et 105 sujets adultes jeunes du Niger. Ils ont constate d'une part qu'il n'y avait aucune difference d'activite entre les deux posologies de praziquantel, d'autre part que tant sur le plan de la prevalence que de l'elimination des œufs, les deux medicaments montrent une efficacite similaire. Toutefois le praziquantel a une action plus rapide mais six mois apres traitement la difference n'est pas significative, 91,9% des malades sont negatives par le praziquantel et 87,3 % par l'oltipraz.

The Centre de Recherche sur les Méningites et les Schistosomes (CERMES) is a research institute depending on the Organisation de Coordination et de Coopération pour la lutte contre les Grandes Endémies--a West African Organization for Public Health--devoted to the studies on schistosomiasis and meningitis. The staff includes 32 persons with 11 scientists and one financial officer. The activities of the CERMES involving schistosomiasis concern three research units: (a) ecology of human and animal schistosomiasis transmission; the CERMES defined the different patterns of schistosomiasis transmission in Niger (involving African dry savana); in this field, we have shown, (i) the existence of important variability in conditions of transmission of S. haematobium and, (ii) natural hybridization between parasitic species of the ruminants (S. bovis and S. curassoni) and genetic interaction between human and animal parasites; (b) definition of morbidity indicators usable for rapid assessment methods, for appraisal of the severity of the disease and for the evaluation of the efficiency of control methods; we have established the correlation between ultrasonographic data and some cheap and simple field indicators; (c) immune response and protective immunity induced by recombinant glutathion S-transferase (Sm28, Sb28 and Sh28) in homologous and heterologous animal models including goats, sheep and non human primates (Erythrocebus patas). In Niger, we participate in all control programs against schistosomiasis to define control strategies, to supervise operations and to participate in their evaluation with external experts. International collaborations constitute a frame including four laboratories in Africa and six laboratories in developed countries (Europe and USA).The Centre de Recherche sur les Meningites et les Schistosomoses (CERMES), a research center in Niamey, Niger, affiliated with a West African public health organization, conducts studies in the areas of parasitology, epidemiology, and immunology. Significant variability in factors related to transmission of Schistosoma haematobium have been noted. Experimental research on the Schistosoma-bulinid compatibility and field surveys of the geographic distribution and role of snails in transmission have been essential to the design of parasite control interventions in West Africa. A CERMES-sponsored project, supported by the European Community, is examining urinary schistosomiasis control in the Niger river valley and the impact of treatment on ultrasonically visualized urologic lesions. The Experimental Vaccine Unit seeks to improve the route of administration and choice of adjuvant and to propose a vaccine protocol for field testing. Recombinant proteins have been found to alter the development of the parasite either by inducing a reduction in the parasite burden or an inhibition of the fecundity of the parasite.