It is generally recommended to perform multiple stool examinations in order to improve the diagnostic accuracy when assessing the impact of mass drug administration programmes to control human intestinal worm infections and determining efficacy of the drugs administered. However, the collection and diagnostic work-up of multiple stool samples increases costs and workload. It has been hypothesized that these increased efforts provide more accurate results when infection and drug efficacy are summarized by prevalence (proportion of subjects infected) and cure rate (CR, proportion of infected subjects that become egg-negative after drug administration), respectively, but not when these indicators are expressed in terms of infection intensity and egg reduction rate (ERR). We performed a meta-analysis of six drug efficacy trials and one epidemiological survey. We compared prevalence and intensity of infection, CR and ERR based on collection of one or two stool samples that were processed with single or duplicate Kato-Katz thick smears. We found that the accuracy of prevalence estimates and CR was lowest with the minimal sampling effort, but that this was not the case for estimating infection intensity and ERR. Hence, a single Kato-Katz thick smear is sufficient for reporting infection intensity and ERR following drug treatment.

Praziquantel is the cornerstone of schistosomiasis control. A number of reports from endemic areas suggest that resistance or tolerance to praziquantel might exist in Schistosoma mansoni. Several explanations were postulated. The present work was designed to test the hypothesis that a low praziquantel (pzq) cure rate in Egypt is due to survival and maturation of immature stages that escaped pzq, which is effective against mature S. mansoni worms only. The study sample included 1351 children attending El Rouse primary school located in El Rouse village, Nile Delta, Egypt. All children received 2 pzq doses (40 mg/kg) 4 weeks apart. Diagnosis of S. mansoni infection and cure assessment were based on examination of 2 Kato slides prepared from a single stool sample collected before and 4 weeks after the first and second treatments. The cure rate was 78·8% after the first treatment and increased significantly to 90·8% after the second treatment. Egg reduction rates were 71·2% and 77·2% after 1 and 2 treatments respectively. Pre-treatment intensity of infection has a great influence on cure and egg reduction rates. Our results confirmed that low praziquantel cure rate, in Egypt, might be attributed, even partially, to survival and maturation of the immature S. mansoni stages that escaped pzq that is effective against mature worms only.

Schistosoma haematobium is refractory to praziquantel (PZQ) during the prepatent period of infection. A hypothesis based on this observation is that in areas where S. haematobium transmission is seasonal, the outcome of chemotherapy depends on the timing of the treatment relative to the annual transmission pattern. To examine this hypothesis, a study was carried out in southern Mozambique. Following demonstration of seasonal transmission, PZQ was administered separately to two cohorts of S. haematobium-infected schoolchildren in (1) the high and (2) the low transmission seasons and followed up after two months when levels of infection and intensities were measured. The prevalence of infection decreased from 54·2% and 51·7% in cohorts 1 and 2 to 30·3% and 1·8%, respectively. The geometric mean intensity of infection decreased from 23·3 eggs/10 ml of urine at baseline to 15·6 eggs/10 ml of urine in cohort 1 (treated during high transmission season), and from 23·5 eggs/10 ml urine to 7·3 eggs/10 ml of urine in cohort 2 (treated during low transmission season). The observed cure rates in cohorts 1 and 2 were 69·7% and 98·2%, respectively. Differences in infection between the cohorts in terms of cure rate and level of infection two months post-treatment were statistically significant and indicate that in areas with a seasonal transmission pattern, the effect of PZQ can be enhanced if treatment takes place during the low transmission season. We conclude that appropriately timed PZQ administration will increase the impact of schistosomiasis control programmes.

The aim of this study was to assess the effect of two doses of 40 mg/kg praziquantel with 2 weeks interval versus a standard single dose of 40 mg/kg on cure rates, egg reduction, intensity of infection, and micro-haematuria in Schistosoma haematobium infections. A randomised controlled intervention study was carried out among school-aged children in two different endemic settings with follow-up at 3, 6 and 18 months following drug administration. Differences in cure rates between the two treatment regimens were not significant. However, in high transmission areas, the double treatment regimen was more effective in egg reduction than single treatment regimen and the difference in egg reduction between the two treatments was significant at 3 months (P<0·005), 6 months (P<0·0001) and 18 months (P<0·003) after treatment. There was a significant difference in the effect of the two treatments on prevalence of micro-haematuria at 18-month follow-up in both Koulikoro (P<0·001) and Selingue (P<0·003). The study shows that although no significant difference could be observed in the overall cure-rates between the two treatment regimens, the effect of double treatment was a significant reduction in infection intensity as well as micro-haematuria which may have a great impact in reducing subtle morbidity.