Efficacy of praziquantel against Schistosoma haematobium infection in children

A study was performed to determine the efficacy of praziquantel (PZQ) against Schistosoma haematobium. Children (n = 592) infected with S. haematobium received either a single treatment with PZQ (40 mg/kg) or two or three treatments with PZQ at three-week intervals after the initial treatment and efficacy was monitored for nine weeks. Cure rates at three-weeks post-treatment were low (< 50%), suggesting either that worms are killed very slowly or, more likely, that eggs continue to be released from tissues after worm death. Interestingly, a single dose of PZQ showed high efficacy (cure rate > 83% and egg reduction rate > 98%) when assessed from six weeks post-treatment onward. There were no significant differences in cure rates or intensity of infection between the three cohorts at any point in the study, despite the different treatment regimens. Since children were in contact with transmission sites during the study period, the results suggest good efficacy of PZQ against all stages of S. haematobium, including the immature worms.     

Evaluation of the In Vivo Activity of Different Concentrations of Clerodendrum Umbellatum Poir Against Schistosoma Mansoni Infection in Mice

Clerodendrum umbellatum Poir (Verbenaceae) is traditionally used in Cameroon for the treatment of many diseases including intestinal helminthiasis. This study was undertaken to assess the in vivo antischistosomal activity of its leaves aqueous extract on a Schistosoma mansoni mice model and to determine the most effective dose of this extract. Mice showing a patent infection of S. mansoni were daily treated with C. umbellatum leaves aqueous extract at the doses of 40, 80 or 160 mg/kg body weight for 14 days. Seven days after administration of the extract, schistosomicidal activity was evaluated on the liver and spleen weights, faecal eggs releasing, liver egg count and worm burden. Treatment using C. umbellatum leaves aqueous extract resulted in an important reduction in faecal egg output by 75.49 % and 85.14 % for 80 mg/kg and 160 mg/kg of the extract respectively. These reduction rates did not differ significantly from the 100 % obtained in the group of infected mice treated with 100 mg/kg of praziquantel. C. umbellatum leaves aqueous extract was lethal to S. mansoni worm. A 100 % reduction rate was recorded in the group of infected mice treated with 160 mg/kg of the extract, as well as in praziquantel-treated mice. An amelioration of the hepatosplenomegaly was noticed in both the extract-treated mice and the praziquantel-treated mice. From these results, we can conclude that C. umbellatum leaves aqueous extract demonstrated schistosomicidal properties in S. mansoni model at doses of at least 80 mg/kg body weight.     

Large-scale determinants of intestinal schistosomiasis and intermediate host snail distribution across Africa: does climate matter?

The geographical ranges of most species, including many infectious disease agents and their vectors and intermediate hosts, are assumed to be constrained by climatic tolerances, mainly temperature. It has been suggested that global warming will cause an expansion of the areas potentially suitable for infectious disease transmission. However, the transmission of infectious diseases is governed by a myriad of ecological, economic, evolutionary and social factors. Hence, a deeper understanding of the total disease system (pathogens, vectors and hosts) and its drivers is important for predicting responses to climate change. Here, we combine a growing degree day model for Schistosoma mansoni with species distribution models for the intermediate host snail (Biomphalaria spp.) to investigate large-scale environmental determinants of the distribution of the African S. mansoni-Biomphalaria system and potential impacts of climatic changes. Snail species distribution models included several combinations of climatic and habitat-related predictors; the latter divided into “natural” and “human-impacted” habitat variables to measure anthropogenic influence. The predictive performance of the combined snail–parasite model was evaluated against a comprehensive compilation of historical S. mansoni parasitological survey records, and then examined for two climate change scenarios of increasing severity for 2080. Future projections indicate that while the potential S. mansoni transmission area expands, the snail ranges are more likely to contract and/or move into cooler areas in the south and east. Importantly, we also note that even though climate per se matters, the impact of humans on habitat play a crucial role in determining the distribution of the intermediate host snails in Africa. Thus, a future contraction in the geographical range size of the intermediate host snails caused by climatic changes does not necessarily translate into a decrease or zero-sum change in human schistosomiasis prevalence.     

Time to set the agenda for schistosomiasis elimination

It is time to raise global awareness to the possibility of schistosomiasis elimination and to support endemic countries in their quest to determine the most appropriate approaches to eliminate this persistent and debilitating disease. The main interventions for schistosomiasis control are reviewed, including preventive chemotherapy using praziquantel, snail control, sanitation, safe water supplies, and behaviour change strategies supported by information, education and communication (IEC) materials. Differences in the biology and transmission of the three main Schistosoma species (i.e. Schistosoma haematobium, S. mansoni and S. japonicum), which impact on control interventions, are considered. Sensitive diagnostic procedures to ensure adequate surveillance in areas attaining low endemicity are required. The importance of capacity building is highlighted. To achieve elimination, an intersectoral approach is necessary, with advocacy and action from local communities and the health community to foster cooperative ventures with engineers, the private sector, governments and non-governmental organizations specialized in water supply and sanitation. Examples of successful schistosomiasis control programmes are reviewed to highlight what has been learnt in terms of strategy for control and elimination. These include St. Lucia and other Caribbean islands, Brazil and Venezuela for S. mansoni; Saudi Arabia and Egypt for both S. mansoni and S. haematobium; Morocco, Tunisia, Algeria, Mauritius and the Islamic Republic of Iran for S. haematobium; Japan and the People's Republic of China for S. japonicum. Additional targets for elimination or even eradication could be the two minor human schistosome species S. guineenisis and S. intercalatum, which have a restricted distribution in West and Central Africa. The examples show that elimination of schistosomiasis is an achievable and desirable goal requiring full integration of preventive chemotherapy with the tools of transmission control. An agenda for the elimination of schistosomiasis would aim to identify the gaps in knowledge, and define the tools, strategies and guidelines that will help national control programmes move towards elimination, including an internationally accepted mechanism that allows verification/confirmation of elimination.     

Polyparasitism with Schistosoma haematobium and soil-transmitted helminth infections among school children in Loum, Cameroon

Prevalence and abundance of Schistosoma haematobium and soil-transmitted helminths (STH) were assessed among a total of 1600 pupils (urine, n = 1190; faecal samples, n = 1454) attending five schools in Loum, Littoral Province, Cameroon, with the specific aim of assessing the extent of polyparasitism and the extent to which infections were focused in particular subsets of the study group. Prevalence of S. haematobium was 62.8% with an abundance (arithmetic mean of egg counts) of 54 eggs/10 ml urine. For the STH these were 47.7% and 619 eggs per gram of faeces (EPG) for Trichuris trichiura, 65.5% and 3636 EPG for Ascaris lumbricoides, and 1.4% and <0.1 EPG for hookworms. Most children (90.3%) were infected with at least one of these four species, the largest proportion (34.3%) carrying two species; 27.4% carried three and 1.1% carried concurrently all four species of parasites. The average number of species harboured increased with age, as did the prevalences of S. haematobium and T. trichiura but not that of A. lumbricoides. All STH showed marked differences in prevalence between the five schools but only T. trichiura varied significantly between sexes. Mean abundance of infection varied significantly between age classes, among schools and between the sexes, with females showing heavier mean EPGs for A. lumbricoides and T. trichiura and males higher mean eggs/10 ml urine for S. haematobium infections. A highly significant association was detected between A. lumbricoides and T. trichiura, that was not context-dependent. This was confirmed in quantitative analyses after controlling for differences in abundance between schools, sexes and age classes. A weaker context-dependent association (prevalence data) was detected between S. haematobium and A. lumbricoides (sex- and age-dependent) but quantitative associations between these two species, as well as between S. haematobium and T. trichiura, were not convincing.     

A Five-Country Evaluation of a Point-of-Care Circulating Cathodic Antigen Urine Assay for the Prevalence of Schistosoma mansoni

We evaluated a commercial point-of-care circulating cathodic antigen (POC-CCA) test for assessing Schistosoma mansoni infection prevalence in areas at risk. Overall, 4,405 school-age children in Cameroon, Côte d''Ivoire, Ethiopia, Kenya, and Uganda provided urine for POC-CCA testing and stool for Kato-Katz assays. By latent class analysis, one POC-CCA test was more sensitive (86% versus 62%) but less specific (72% versus ∼100%) than multiple Kato-Katz smears from one stool. However, only 1% of POC-CCA tests in a non-endemic area were false positives, suggesting the latent class analysis underestimated the POC-CCA specificity. Multivariable modeling estimated POC-CCA as significantly more sensitive than Kato-Katz at low infection intensities (< 100 eggs/gram stool). By linear regression, 72% prevalence among 9–12 year olds by POC-CCA corresponded to 50% prevalence by Kato-Katz, whereas 46% POC-CCA prevalence corresponded to 10% Kato-Katz prevalence. We conclude that one urine POC-CCA test can replace Kato-Katz testing for community-level S. mansoni prevalence mapping.     

A single-strand conformation polymorphism (SSCP) approach for investigating genetic interactions of <Emphasis Type="Italic">Schistosoma haematobium</Emphasis> and <Emphasis Type="Italic">Schistosoma guineensis</Emphasis> in Loum,Cameroon

Single-strand conformation polymorphism (SSCP) analysis of the second internal transcribed spacer (ITS2) of nuclear ribosomal DNA provides a molecular tool for the identification of Schistosoma haematobium, Schistosoma guineensis and the hybrids of these two species. This molecular tool was utilized to provide a detailed analysis of the interactions between S. haematobium and S. guineensis in hybrid zones of Loum, Littoral Province, Cameroon. Individual hybrid schistosomes were identified within the natural populations collected from Loum in 1990, 1999 and 2000, which would have been misidentified as S. haematobium using solely morphological and sequence criteria. This study indicates the complexities of the hybridization between S. haematobium and S. guineensis and emphasizes the importance of assessing morphological, biological and molecular data to gain insights into the interaction of these two species over time.     

Control of schistosomiasis: challenge and prospects for the 21st century

Schistosomiasis occurs throughout the developing world and remains a major public health problem in the poorest communities with enormous consequences for development. More than 200 million people are infected and this poverty-related disease is highly prevalent in sub-Saharan Africa. The extent of the problem has long been neglected because the disease rarely kills and due to its insidious nature, signs and symptoms are taken seriously only after permanent impairment has occurred. Moreover; as many other poverty-related communicable diseases, schistosomiasis has been overshadowed by other health priorities. Today schistosomiasis control is a priority on the agenda of many governments, donors and international agencies. A momentum as well as an unprecedented opportunity do exist for cost-effective action. Importantly, the renewed impetus for schistosomiasis control throughout sub-Saharan Africa reinforces the need for operational research to improve our understanding of the disease. The strengthening of the national capacity in endemic countries, a greater commitment of governments and communities from these developing countries, and an efficient stakeholder coordination are vital for a successful and durable control. The paper highlights the current opportunities and challenge for schistosomiasis control for the 21st century. By working all together, we have a great opportunity to take up the challenge and to improve the health of the poor.     

A neotropical snail host of Schistosoma mansoni introduced into Africa and consequences for the schistosomiasis transmission Biomphalaria tenagophila in Kinshasa (Democratic Republic of Congo)

Malacological surveys carried out in the early 1970s in water bodies of the Kinshasa area, Lower Zaire (Democratic Republic of Congo), showed the appearance of a Biomphalaria species which was identified as Biomphalaria camerunensis. In 1976, other surveys confirmed the presence of the species in several sites and showed numerous infected snails with Schistosoma mansoni, demonstrating for the first time an active transmission of the parasite responsible of the intestinal schistosomiasis in this area. The most recent malacological sampling was carried out by one of us in 1994 in Mangungu River and revealed the presence of apparently the same snail species. However, conchological, anatomical and molecular studies showed that this snail may be considered as an introduced neotropical species, B. tenagophila. To our knowledge, this is the second example of the introduction of a neotropical snail host of schistosomes into Africa.