A three year follow-up of chemotherapy with praziquantel in a rural Zambian community endemic for schistosomiasis mansoni

A meta-analysis of changes in schistosomiasis prevalence in Zambia: implications on the 2020 elimination target

Schistosomiasis affects more than 4 million school-aged children in Zambia, mostly in rural communities due to unsafe water and inadequate sanitation facilities. Although several studies were done in Zambia between 1976 and 2019, empirical estimates of the disease burden remain unavailable. Therefore, appraisal of the current schistosomiasis burden is pertinent in the re-evaluation of schistosomiasis-control strategies in Zambia. A random-effect model was used to estimate the prevalence of schistosomiasis infection in Zambia across different age groups for the period between 1976 and 2019. A literature search was done in the following databases: PubMed, ISI Web of Science, Google Scholar, CINAHL, and African Journals Online. Twenty-eight studies with relevant prevalence data were identified and included in the analysis. The pooled prevalence estimate of Schistosoma haematobium and Schistosoma mansoni across studies for the entire period was 35.5% (95% CI: 25.8-45.9) and 34.9% (95% CI: 20.7-50.6), respectively. Prevalence estimates among school-aged children for S. haematobium and S. mansoni were 32.2% (95% CI: 21.1-44.7) and 18.1% (95% CI: 3.0-38.4), respectively. The reported pooled prevalence estimate for S. haematobium among the adults was 54% (95% CI: 23.2-83.7). Only two studies collected information from preschool aged children. Substantial heterogeneity (I² = 100%, p < 0.0001) was observed among the studies. Although a reduction in disease prevalence was observed from 1990 to 2010, this was not sustained after 2010. In this meta-analysis, S. haematobium was more prevalent compared to S. mansoni, with more cases observed among school-aged children (SAC). Thus, control programs should target age groups that are highly infected or are at high risk of infection.

Sustaining Control of Schistosomiasis Mansoni in Western Côte d'Ivoire: Results from a SCORE Study, One Year after Initial Praziquantel Administration

Background

The Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) has launched several large-scale trials to determine the best strategies for gaining and sustaining control of schistosomiasis and transitioning toward elimination. In Côte d’Ivoire, a 5-year cluster-randomized trial is being implemented in 75 schools to sustain the control of schistosomiasis mansoni. We report Schistosoma mansoni infection levels in children one year after the initial school-based treatment (SBT) with praziquantel and compare with baseline results to determine the effect of the intervention.

Methodology

The baseline cross-sectional survey was conducted in late 2011/early 2012 and the first follow-up in May 2013. Three consecutive stool samples were collected from 9- to 12-year-old children in 75 schools at baseline and 50 schools at follow-up. Stool samples were subjected to duplicate Kato-Katz thick smears. Directly observed treatment (DOT) coverage of the SBT was assessed and the prevalence and intensity of S. mansoni infection compared between baseline and follow-up.

Principal Findings

The S. mansoni prevalence in the 75 schools surveyed at baseline was 22.1% (95% confidence interval (CI): 19.5–24.4%). The DOT coverage was 84.2%. In the 50 schools surveyed at baseline and one year after treatment, the overall prevalence of S. mansoni infection decreased significantly from 19.7% (95% CI: 18.5–20.8%) to 12.8% (95% CI: 11.9–13.8%), while the arithmetic mean S. mansoni eggs per gram of stool (EPG) among infected children slightly increased from 92.2 EPG (95% CI: 79.2–105.3 EPG) to 109.3 EPG (95% CI: 82.7–135.9 EPG). In two of the 50 schools, the prevalence increased significantly, despite a DOT coverage of >75%.

Conclusions/Significance

One year after the initial SBT, the S. mansoni prevalence had decreased. Despite this positive trend, an increase was observed in some schools. Moreover, the infection intensity among S. mansoni-infected children was slightly higher at the 1-year follow-up compared to the baseline situation. Our results emphasize the heterogeneity of transmission dynamics and provide a benchmark for the future yearly follow-up surveys of this multi-year SCORE intervention study.

Schistosomiasis is a parasitic worm disease that is widespread in sub-Saharan Africa. To better understand how to gain and sustain the control of schistosomiasis and how to eliminate this disease in different epidemiologic settings, the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) has launched several multi-year studies that are being implemented in East and West Africa. This article highlights how the Schistosoma mansoni infection levels changed one year after an initial treatment with the anti-worm drug praziquantel given to children aged 5–15 years in western Côte d’Ivoire. Infection and treatment data at school level were available from more than 4,600 children in 50 schools. One year after the treatment that had been received by more than 80% of the children, the overall S. mansoni prevalence decreased from 19.7% to 12.8%, while the intensity of infection among S. mansoni-positive children slightly increased. In several schools, the S. mansoni intensity and, particularly the prevalence, increased unexpectedly. Our findings show that the dynamics of schistosomiasis transmission varies from one village to another. It will be interesting to monitor changes over longer time periods as this SCORE study unfolds.

Use of praziquantel against schistosomiasis: a review of current status

Praziquantel therapy has become an important component of any programme directed towards schistosomiasis control. This disease being prevalent in many disadvantaged countries, where the means and resources are limited, the strategies for its control on a large scale are also beset with various other constraints. In this review, the potentials of praziquantel therapy in containing the intensities, prevalences and schistosomiasis-associated morbidities in endemic areas of different geographical and epidemiological settings are examined. By and large, regular community-based treatment produces a longer term favourable impact on infection levels and morbidity, but the impact on the disease transmission appears limited. Children constitute a high risk group in schistosomiasis. They are usually subjected to more rapid and intense reinfection, but they also appear more responsive to praziquantel therapy in preventing or reversing the effects of the disease. Modern techniques used in the assessment of impact of praziquantel treatment in schistosomiasis control are outlined.

Characterization and expression of a novel cystatin gene from Schistosoma japonicum

Cystatins are a family of cysteine protease inhibitors that play a crucial role in the immune evasion from their host and in the adaptation to host defence. Here, we isolated a full-length cDNA sequence inferred to encode a novel cystatin gene from a blood fluke, Schistosoma japonicum. The cDNA, designated SjCystatin, comprised an open reading frame (ORF) of 306 bp, and encoded 101 amino acids with a predicted molecular weight of 11.3 kDa. This predicted protein shared a significant degree of sequence identity with the type I cystatin (stefin) of Schistosoma mansoni and Homo sapiens. These proteins exhibited a typical cystatin topology, including the absence of disulfide bonds and three conserved catalytic motifs, Gly at the N-terminus (Gly(6)), Gln-X-Val-X-Gly motif (Q(49)VVAG(53)) and an LP pair at the C-terminus (L(76)P(77)). The SjCystatin gene spanned 376 bp and contained three exons. The positions of two introns were conserved between the cystatin genes of trematodes and their vertebrate hosts. Reverse transcription polymerase chain reaction confirmed the transcription of SjCystatin in the egg, schistosomula and adult stages of S. japonicum. The encoding ORF region was cloned into pET-28a (+) prokaryotic expression vector. After purification, the recombinant protein SjCystatin (recSjCystatin), expressed in Escherichia coli, was used to immunize animals and produce its specific polyclonal antibody. Western blot analysis revealed that the native SjCystatin was expressed in the egg and adult stages. The enzyme activity assay of the recSjCystatin showed that it inhibited the proteolytic activity of papain. SjCystatin protein was mainly localized on the miracidium within eggs. Immunohistochemistry revealed that SjCystatin mainly localized in the epithelial cells lining the gut as well as the tegument on the surface of adult worms. The conserved genomic DNA structure among cystatin homologues of trematode and their vertebrate host emphasized the characteristics of compatibility between parasites and their hosts. This study provides the first insight into the gene and protein of S. japonicum cystatin and a basis for a further understanding the functions of this gene.

A community-based randomized trial of praziquantel to control schistosomiasis morbidity in schoolchildren in Zambia

A community-based, double-blind, randomized trial of praziquantel was carried out in an area of Zambia endemic for schistosomiasis. The aim of the study was to assess the impact of the treatment on Schistosoma mansoni morbidity. A total of 377 infected children, aged seven to 19 years, was randomized into two groups: one of 190 (group A) and one of 187 (group B). All children were treated with 40 mg praziquantel/kg at the start of the study. Six months later, the children in group A were re-treated with the same dose of praziquantel, while the children in group B were given placebos. All children were followed up three, six and 12 months after the initial treatment, morbidity being clinically evaluated at the six- and 12-month follow-ups. The results show that, in both groups of children, there were significant reductions in splenomegaly, hepatomegaly, and subjective symptoms of morbidity six and 12 months after initial treatment. However, there were no significant differences, between the two groups, in the prevalences of these symptoms of morbidity. It therefore appears that once-yearly treatment of children, in this and similar endemic areas, is sufficient to reduce schistosomiasis morbidity to, and maintain it at, a tolerable level.

Comparison of different chemotherapy strategies against Schistosoma mansoni in Machakos District, Kenya: effects on human infection and morbidity

A comparison was made of the long-term impact of different methods of administration of chemotherapy (oxamniquine, 30 mg/kg in divided doses; or praziquantel, 40 mg/kg) on prevalence and intensity of Schistosoma mansoni infection in four areas in Kangundo Location, Machakos District, Kenya. In Area A, treatment was offered in October 1983 and again in April 1985 to all infected individuals. In Area H, treatment was offered in April 1985 to individuals excreting greater than or equal to 100 eggs per gram (epg) of faeces. In Area S, treatment was offered in April 1985 to all infected school children, within the framework of the primary schools. In the witness area, Area W, treatment was given in April 1985, for ethical reasons, to a small number of individuals excreting greater than or equal to 800 epg. Prevalence and intensities of infection were subsequently monitored at yearly intervals for three complete post-treatment years. In the Area S schools, clinical examination was also carried out at yearly intervals. Treatment of all infected individuals on two occasions (Area A) was the most effective and long-lasting way of reducing prevalence and intensity of infection. In this area, however, some earlier interventions had been carried out and pre-treatment intensities were lower than in the other areas. Treatment only of infected schoolchildren (Area S) also had a marked and prolonged effect, comparable to or better than treatment of individuals with heavy infections (Area H). Treatment of infected schoolchildren also caused a persistent reduction in the prevalence of hepatomegaly, and there was suggestive evidence from intensities of infection in community stool surveys (but not from incidence rates) of an effect on transmission. In all study areas, reinfection was most rapid and most intense among children. These findings are discussed in the light of theoretical considerations and of results from other studies, both on schistosomiasis and on intestinal helminths. We conclude that, in areas of low morbidity such as Kangundo, chemotherapy of schoolchildren only, at intervals of up to 3 years, is a satisfactory way of producing a long-term reduction in both intensity of infection and morbidity.

Reinfection after treatment of schistosome infections

Today, chemotherapy has a central role in the control of schistosome infections. Although the costs involved may be high in relation to local expenditures on health, externally funded mass treatment programmes can lead to large reductions in the prevalence and intensity of schistosome infections. But the benefits of treatment to a community that has been involved in a mass chemotherapy programme, or to an individual patient seen in a health centre, will be limited if reinfection after treatment is rapid and intense. Despite the efficacy of the available drugs few, if any, control programmes based on mass chemotherapy have interrupted transmission and come anywhere near to eradicating schistosome infection.