Schistosomiasis is a public health problem worldwide [1,2,3]. It is the second most deadly parasitic cause after malaria, endemic in 74 countries. Approximately 261 million people are infected worldwide, and nearly 800 million people are exposed to the disease [3,4]. Sub-Saharan Africa (SSA) is the most affected region, accounting for 90% of infections [5,6]. It is considered a disease of poverty, and unequally affects the less wealthy [7,8]. The Schistosoma haematobium and Schistosoma mansoni species are responsible for the burden of schistosomiasis, although the Schistosoma haematobium species (S. haematobium) is more widespread in the sub-Saharan region [9]. Infection can occur when humans come into contact with schistosome larvae in water, which are cercariae released by intermediate snail hosts [10,11]. The supply of safe drinking water and improved hygiene and sanitation, combined with preventive chemotherapy using praziquantel, are considered the basic strategies for reducing the burden of schistosomiasis [11]. Environmental concerns and the high costs associated with intermediate host control hinder the realization of a successful global schistosomiasis control strategy [12]. Good progress in reducing schistosomiasis morbidity and mortality has been made in Brazil, Cambodia, Egypt, China and the Philippines [13]. Since 1984, the World Health Organization (WHO) has approved a drug treatment, praziquantel (PZQ), a broad-spectrum anthelmintic aimed at reducing the morbidity of Schistosoma infection [3]. A standard single oral dose of 40 mg/kg bodyweight remains the drug recommended by the World Health Organization for community- and school-based mass treatment (CT) [10,11]. Every year, endemic African countries receive praziquantel to treat and prevent schistosomiasis in millions of school-age children [14,15]. Compliance with the treatment is difficult, particularly among people living in disadvantaged socio-economic areas due to fear of adverse effects and the apparent absence of disease symptoms, and even when symptoms do appear, they are often stigmatized [16,17] or considered a normal sign of puberty, not requiring treatment [18,19]. Tremendous efforts have been made to eliminate schistosomiasis over the last decade by the World Health Organization, having set the goal of interrupting transmission in endemic African countries by 2030 [20]. Government agencies in several countries have given priority to controlling neglected tropical diseases (NTDs) by exploiting the lifestyle of intermediate hosts throughout their cycle, such as implementing snail control and improving sanitation and access to safe, clean water [21,22]. School-age children are the main targets for control, as they are considered the most at risk of infection. They are most likely to take part in daily activities such as fishing, rice growing and swimming, which expose them to a higher risk of infection compared to other age groups [23]. Protective immune responses against schistosomes develop slowly, while children in schistosomiasis-endemic areas are generally susceptible to reinfection after treatment for schistosomiasis [23]. Despite annual or two-yearly treatments, it has been reported that reinfection occurs in endemic areas in less than 12 months in several treated children [24]. This highlights the need for further investigations into the efficacy of praziquantel against Schistosoma haematobium in endemic areas of sub-Saharan Africa. In Mali, few studies have been carried out on reinfection after treatment, so it was necessary to review articles published in the sub-Saharan African region between 2005 and 2020 that address the efficacy of praziquantel in the treatment of schistosomiasis in school-age children, with a view to informing decision-makers.

As part of the article search, Google Scholar provided six hundred and thirty-three (633) records. We obtained 13 articles that were registered from the PubMed database. Overall, we registered a total of 620 articles after removing duplicates (Figure 1). Of the 620 articles, 609 were deemed ineligible according to our inclusion criteria. We had a total of 11 articles eligible for review, including field studies investigating the efficacy of praziquantel-based treatment against Schistosoma haematobium in school-aged children in sub-Saharan African countries at the community or school level from 2005 to 2020. Articles excluded were those that included adults, those published before 2005 and after 2020, studies on the efficacy of praziquantel in combination with other drugs and studies on the side effects of the treatment.

Our review was based on the efficacy of praziquantel in school-aged children infected with urogenital schistosomiasis in sub-Saharan Africa from 2005 to 2020. Praziquantel has been shown to be effective against Schistosoma haematobium at a single standard dose of 40 mg/kg body weight [9,27,33,35,38]. Thus, to eliminate the infection, the need for a further dose in some countries with low cure rates has been reported [25,27,29,35]. In fact, praziquantel is ineffective against juvenile schistosomes, which can then mature and release eggs [35,39]. After treatment with praziquantel, infection may persist due to the activity of children in contact with contaminated water [26,28]. Reinfection is possible when children, after successful treatment with praziquantel, resume activities involving contact with cercarial-infested water, hence the need for health education to reduce water contact [26,29]. In our review, one case of treatment failure was reported in children with a high intensity of infection [27,33,35]. This was due to poor absorption of the drug rather than parasite resistance, which has been associated with the ineffectiveness of praziquantel [40,41]. However, constant monitoring of praziquantel efficacy is important while awaiting the discovery and development of new drugs [27,32,35,40]. It would also be advantageous to consider taking therapeutic doses of praziquantel at different time intervals as it has been reported that a double dose of 40 mg/kg administered over a four-week interval is more effective than a single treatment in endemic areas [27,36]. Thus, in studies where the dose was repeated over a four-week interval, few treated cases continued to release viable eggs [42]. However, the mass distribution of praziquantel-based drugs raises concerns about possible resistance [9,43]. Follow-up after mass distribution is necessary in most cases, as praziquantel is the only drug for schistosomiasis at 40 mg/kg body weight [44,45]. Since a single dose does not completely eliminate the parasite [25,27,29,35]. It is important to conduct educational awareness campaigns to warn residents of the risk factors associated with schistosomiasis reinfections [9,46]. In addition, supplying drinking water by installing new boreholes or reactivating old boreholes or wells in these communities could reduce host–vector contact [5,26,35]. This supply of drinking water could also reduce the incidence of frequent schistosomiasis infections [5,26,35]. In the context of drug administration, papers that have repeatedly used the standard dose of 40mg/kg have shown efficacy in reducing the intensity of infection after the second dose [26,27,35]. The reasons for administering the second dose were to target immature worms not eliminated by the first treatment and to do so between eight and twenty-eight weeks after the initial treatment [26,27,35]. Infection may persist after treatment due to the reduced sensitivity of immature parasites to the drug. Thus, they may develop tolerance or resistance over time [47,48]. Non-viable eggs may be present for months in the urine of patients treated for Schistosoma haematobium and will falsely limit the results of egg reduction and cure rates [49]. The efficacy of mass treatment has been shown to reduce the prevalence of infection, but soon after drug distribution is interrupted, prevalence rapidly returns to pre-intervention levels [32]. This has prompted researchers to conduct trials with a single dose of 60 mg/kg body weight to prevent failure/resistance [50]. Investigators who have conducted comparative studies of praziquantel with the standard dose of 40 mg/kg versus the 60 mg/kg body weight split dose have reported divergent results on the efficacy of schistosomiasis treatment [51,52].

In addition, several authors have reported that the efficacy of praziquantel at a single dose of 60mg/kg body weight is similar to that of the 40 mg/kg body weight dose [44,51,53]. A dose higher than 40 mg/kg of body weight does not therefore provide any added value in the treatment of Schistosoma haematobium infection [43,45,51]. Today, the fight against schistosomiasis is still based on the large-scale treatment of at-risk population groups, access to drinking water, improved sanitation, hygiene education, behavioral change, gastropod control and environmental management [22]. The new Roadmap for Neglected Tropical Diseases 2021-2030, adopted by the World Health Assembly, has set the global objective of eliminating schistosomiasis as a public health problem in all endemic countries and interrupting transmission (the absence of infection in humans) in certain countries [54]. The WHO focuses its control strategy on reducing morbidity through regular, targeted praziquantel treatment as part of the large-scale treatment (chemoprophylaxis) of at-risk populations [9]. All at-risk groups receive regular treatment. In countries where transmission is low, the aim should be to interrupt transmission. Access to gray literature and the similarity of the content of the search databases were limitations of this review.

This review has shown that praziquantel is effective against Schistosoma haematobium. It also revealed that praziquantel administered at a standard repeated dose of 40 mg/kg body weight over a four-week interval is more effective than the standard single dose of 40 mg/kg body weight. However, cases of therapeutic failure and reinfection have been reported. It is therefore important to monitor the efficacy of praziquantel while awaiting the discovery and development of new drugs against this parasite. However, proximity to watercourses and participation in water-related activities such as fishing and farming are important factors predisposing children to reinfection after treatment. Treatment with two doses per year in areas of high transmission and once a year in areas of low transmission could minimize the risk of reinfection in children, in addition to other preventive measures.