Dick De Clercq

Efficacy of artesunate and praziquantel in Schistosoma haematobium infected schoolchildren

Praziquantel is the current mainstay for morbidity control of schistosomiasis. Artemisinin and its derivatives, widely used for the treatment of malaria, also display antischistosomal properties. The present study is an effort to assess the therapeutic efficacy of artesunate, an artemisinin derivative, in Schistosoma haematobium infections in a human population. The efficacy of artesunate and praziquantel were comparatively studied in primary schoolchildren from two villages, Lampsar (n=180) and Makhana (n=108), located along the Lampsar river in the delta of the Senegal River Basin in Northern Senegal (West Africa). In each village, half of the infected children were treated with a single oral dose of 40 mg/kg praziquantel and half with artesunate following the recommended malaria monotherapy regimen. For both drugs, cure and egg count reduction rates were, without apparent explanation, higher in Makhana than in Lampsar. In both villages, high and nearly comparable egg count reduction rates were obtained with both drugs at each follow-up after treatment (5, 12 and 24 weeks) in the heavy infected group of children (>50 eggs/10 ml of urine). No major adverse effects were observed. The results demonstrate that artesunate is effective against S. haematobium, but the results obtained with praziquantel were consistently better.

Comparison of the efficacy of mebendazole, albendazole and pyrantel in treatment of human hookworm infections in the Southern Region of Mali, West Africa

A randomized, placebo-controlled trial of the efficacy of pyrantel (single dose 12.5 mg/kg bodyweight), mebendazole (single 500 mg dose) and albendazole (single 400 mg dose) in the treatment of hookworm infections (Necator americanus) was carried out in January 1998 in the Southern Region of Mali, West Africa, during the period of Ramadan (Islamic fast). Statistical analysis of the pre-intervention faecal egg counts showed that there was a significant pre-treatment chance bias, despite randomization of subjects into treatment groups, arising from the main effect of sex (heavier infections among males) and a sex x treatment interaction (the sex bias was not evident in the pyrantel-treatment group). The participants were re-examined 10 days after treatment, and after controlling for the drift in faecal egg counts in the placebo-treated subset, age, sex, fasting and intensity of infection, albendazole was clearly the most effective drug showing consistently efficacies in the range 92.1 to 99.7%, depending on the method of evaluation and the particular subset of the treatment group. Neither mebendazole nor pyrantel was as effective, with efficacies ranging from 60.9 to 89.8% and 4.8 to 89.7%, respectively. Fasting made no difference to drug efficacy. On the basis of our results the single 400 mg dose of albendazole is the treatment of choice for hookworm infections in this region of Mali. We emphasize the need for standardization of the methods used for trial designs, for calculation of summary data relating to drug efficacies and the accompanying statistical tests.

What is the effect of combining artesunate and praziquantel in the treatment of Schistosoma mansoni infections

Summary A group of 110 individuals with Schistosoma mansoni infection was investigated. Patients were allocated to one of three treatment groups and given artesunate or praziquantel alone or both in combination. Combined artesunate–praziquantel significantly increased the number of individuals cured at 5 weeks post‐treatment, but at 12 weeks was only better than artesunate alone and at 24 weeks there was no statistically significant difference between the three groups. Egg count reduction rate was similar to the rate obtained with praziquantel used alone.

Studies on the biology of schistosomiasis with emphasis on the Senegal River basin.

The construction of the Diama dam on the Senegal river, the Manantali dam on the Bafing river, Mali and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni in Northern Senegal, associated with high intensity of infections, due to intense transmission, and the creation of new foci of S. haematobium. Data on the vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard Toll, Senegal are presented with sympatric and allopatric (Cameroon) S. mansoni. Comparisons are made on infectivity, cercarial production, chronobiology of cercarial emergence and longevity of infected snails. Recent data on the intermediate host specificity of different isolates of S. haematobium from the Lower and Middle Valley of the Senegal river basin (SRB) demonstrate the existence of at least two strains of S. haematobium. The role of Bulinus truncatus in the transmission of S. haematobium in the Lower and Middle Valleys of the SRB is reviewed. Both S. haematobium and S. mansoni are transmitted in the same foci in some areas of the SRB.

The epidemiology of a recent focus of mixed Schistosoma haematobium and Schistosoma mansoni infections around the "Lac de Guiers" in the Senegal River Basin Senegal.

Summary A village with mixed Schistosoma mansoni and S. haematobium infections (probably in a early endemic phase) was identified around the Lac de Guiers in the Senegal River Basin. In documenting the epidemiology of both schistosomes, we focused on prevalence and intensity of infection, transmission patterns and the impact of treatment. S. mansoni prevalences (near 100%) and egg counts (overall geometric mean eggs per gram of faeces (epg) of 589 were high in all age groups, with 35% of individuals excreting > 1000 epg, and showing a slow decline in egg output only after the age of 30 years. The overall prevalence (28%) and egg counts (2% > 50 eggs/10 ml) of S. haematobium were low, with mean counts of 6.3 eggs/10 ml. Maximal mean S. mansoni egg counts were found in 5–9 year‐old boys and in 15–19 year‐old girls; S. haematobium maximal counts in 1–4 year‐old boys and in girls aged 5–9. Extremely high Biomphalaria pfeifferi infection ratios were recorded over the whole year. Following a single treatment, re‐infection was rapid with prevalences and mean egg counts of both Schistosoma species reaching pretreatment levels within 7 months.

Observations on the compatibility between Bulinus spp. and Schistosoma haematobium in the Senegal River basin

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 in the Senegal River basin (SRB), in the Lower Valley (Mbodiene), Middle Valley (Podor, Diatar and 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 transmitted by B. globosus, was incompatible 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. truncatus, 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.

Implication of Bulinus truncatus in the transmission of urinary schistosomiasis in Senegal, West Africa.

Abstract Studies on the compatibility between Bulinus truncatus and Schistosoma haematobium from various areas in the Senegal River basin (SRB) were carried out, to investigate the role of B. truncatus in the epidemiology of urinary schistosomiasis in Senegal. The results show that B. truncatus from the Lower Valley is not compatible with S. haematobium from the Middle Valley. Interestingly, the study reveals that B. truncatus from the Upper Valley is compatible with S. haematobium from the same area, and that S. haematobium from the Middle Valley is compatible with B. truncatus from the Lower Valley. Bulinus truncatus naturally infected with S. haematobium have been collected from the Upper Valley of the SRB. These results indicate that B. truncatus is involved in the urinary schistosomiasis in Senegal.