Efficacy and Safety of Praziquantel for Treatment of Schistosoma mansoni Infection among School Children in Tanzania

Single-dose targeted praziquantel preventive chemotherapy is the WHO-recommended intervention for schistosomiasis control in endemic countries. The objective of this study was to assess the efficacy and safety of single-dose praziquantel among Schistosoma mansoni-infected children in north-western Tanzania. A prospective safety and efficacy surveillance study was conducted among 341 school-going children treated with a single-dose praziquantel 40 mg/kg body weight. Socio-demographic, pre-treatment, and post-treatment stool examination and safety data were collected. The primary and secondary outcomes were treatment efficacy (parasitological cure and egg reduction rates at three weeks post-treatment) and treatment-related adverse events, respectively. The overall cure rate and egg reduction rate were 81.2% (76.8–85.3%) and 95.0% (92.7–97.3%), respectively. There was no significant association between cure rate and pre-treatment infection intensity. The incidence of treatment-associated adverse events was 28.5% (23.7–33.3%), with abdominal pain being the most common. Post-treatment abdominal pain and vomiting were significantly associated with pre-treatment infection intensity (p < 0.001) and anemia (p = 0.03), respectively. Praziquantel single-dose is still safe and efficacious against Schistosoma mansoni infection. However, the lack of cure in about one-fifth and adverse events in a quarter, of the infected children indicate the need for close praziquantel safety monitoring and treatment optimization research to improve efficacy.


Introduction
Schistosomiasis is a treatable and preventable neglected tropical disease (NTD) which continues to affect the health and lives of many people, especially children in Sub-Saharan Africa (SSA) [1,2]. The disease is among parasitic diseases of public health importance globally and particularly in Sub-Saharan African countries, including Tanzania [1]. Globally, more than 779 million people are at risk of schistosomiasis infection, and more than 240 million people are infected [3][4][5][6]. More than 90% of the global burden of schistosomiasis is contributed by cases in SSA [7]. Despite being a treatable and preventable disease, schistosomiasis still causes up to 280,000 deaths annually in SSA [4,8]. In Tanzania,

Socio-Demographic and Baseline Characteristics of the Studied Population
A total of 341 school children infected with intestinal schistosomiasis were enrolled in this study. The mean age of the studied population was 11.8 ± 1.7 years. The majority of the study participants were females (53.1%). At enrolment, about one-fifth (20.8%) of the study participants reported a history of pre-treatment abdominal pain. Before treatment, most of the study participants had moderate infection intensity (44.6%). The mean ± standard deviation of egg count/gram of stool was 365.1 ± 437.4, and the median was 222 (IQR 96-471). Stunting and wasting were 34.3% (95% CI = 29.2-39.5%) and 10.0% (95% CI = 6.8-13.2%), respectively. The median hemoglobin concentration was 12.7 g/dL (IQR 11.6-13. 5) ( Table 1).

Cure Rate and Egg Reduction Rate
Assessment of praziquantel for the treatment of schistosomiasis was done using cure rate (CR) and egg reduction rate (ERR) following the WHO guideline [30]. The CR was defined as the proportion of treated persons who were egg-positive at baseline but became egg-negative three weeks after baseline treatment. Of the 341 study participants, 277 (81.2%, 95% CI = 76.8-85.3%) achieved parasitological cure. Though not statistically significant (p = 0.79), adolescents (>12 years) were more cured (82.1%) compared to pre-adolescents (80.9%). There was no statistically significant difference in CRs between females and males (p = 0.58). Pre-treatment infection intensity (p = 0.51), stunting (p = 0.39), wasting (p = 0.27), and anemia (p = 0.07) were not significantly associated with parasitological cure ( Table 2). The proportions of the participants with intestinal schistosomiasis infection across all levels of infection intensities after treatment were significantly lower compared to those before treatment in the studied populations (p < 0.0001) ( Table 3). Variables with a p-value of < 0.3 (age, anemia, height, and baseline infection intensity) on univariate regression analysis were included in the multivariate regression model. All variables were not significant predictors of cure (p > 0.05). The Hosmer and Lemeshow test for the goodness of fit for multivariate analysis model was a good fit (χ 2 = 5.42, p = 0.71) ( Table 4).  The overall ERR was found to be 95.0% (95% CI = 92.7%-97.3%). Though not significant, the ERR was higher in the adolescent age group (97.6%) compared to the pre-adolescent age group (93.6%) (p = 0.12). Males were found to have relatively higher ERR (96.0%) compared to females (94.2%) (p = 0.45). Table 5 presents arithmetic means of the egg count at baseline, follow up visit, and ERRs stratified by age group and sex.

Treatment-Associated Adverse Events
Overall, 97 (28.7%, 95% CI = 23.7-33.3%) of the study participants experienced adverse events within four hours of post-praziquantel administration. A total of 91 (26.7%) participants experienced post-treatment abdominal pain, and 6 (1.8%) participants vomited (two hours post-drug administration). No other gastrointestinal symptoms, including nausea and diarrhea, were observed. No neurological symptoms such as dizziness, fainting, headache were observed. Almost all observed post-treatment abdominal pain and vomiting events were mild and resolved within four hours of drug administration. There was no statistically significant association between CR and post-treatment abdominal pain (p = 0.36) or vomiting (p = 0.31). The observed post-treatment abdominal pain was significantly associated with pre-treatment infection intensity (p < 0.001), but not with age (p = 0.16) or sex of the study participant (p = 0.25). Of those who reported abdominal pain, most had either moderate infection (25.7%) or heavy infection (40.2%), and only 12.6% had a light infection. Vomiting was significantly associated with anemia (p = 0.03) but not with age (p = 0.18) or sex (p = 0.69). Participants who were anemic experienced vomiting more (5.2%) compared to those without anemia (0.8%) ( Table 6).

Discussion
We conducted an observational safety and efficacy surveillance study of a single-dose praziquantel 40 mg/kg body weight administered for the treatment of intestinal schistosomiasis among school children living in a rural area along the shore of Lake Victoria in north-western Tanzania. The study area is known to have a high prevalence of schistosomiasis despite repeated praziquantel MDA. Efficacy was assessed using both CR and ERR after a three week follow up period (21 days), as recommended by the WHO [30]. Our results indicate a high CR (81.2%) and ERR (95.0%) of praziquantel against S. mansoni infection. A single dose praziquantel treatment resulted in a significant reduction in the infection intensity (Table 3). Overall, a small proportion of infected children (12.3%) remained with light infection, and very few participants (5.6%) with moderate or heavy infections (0.9%) after treatment. This finding indicates that praziquantel reduces schistosomiasis-associated morbidities attributed to moderate and heavy S. mansoni infection in children. The observed CR (81.2%) in this study falls within the documented range of 60-90% for S. mansoni infection [10]. The WHO guideline for assessing the efficacy of praziquantel against schistosomiasis states that an ERR of >90% is satisfactory [30]. The observed high CR and ERR in this study indicate that praziquantel is still efficacious against this species of Schistosoma, and praziquantel can still be used by the national NTD control programs in MDA among school children and other at-risk groups in Tanzania.
Safety and efficacy surveillance reports are important to inform the WHO and the national NTD control programs on the current status of the drug efficacy for close follow ups and decision making. To date, there is no alternative drug to treat schistosomiasis. Since 1984, praziquantel has been extensively and repeatedly used in large-scale MDA programs for the control and prevention of schistosomiasis. Praziquantel's low CR may be due to the increased number of MDA rounds [13]. Thus, continuous close monitoring of praziquantel efficacy in endemic countries, particularly in high transmission areas, is vital for the early detection of drug tolerance or resistance. To justify the need for a regular assessment of praziquantel efficacy, a recent study in Cote d'Ivoire reported a much lower CR (69%) at 21-25 days follow up among school children infected with S. mansoni [20].
Despite the observed higher CR of praziquantel, about one-fifth of the children (18.8%) were not cured of the diseases at three weeks post-treatment in this study. The observed 18.8% non-cure rate in our study cannot be attributed to reinfection, since the stool examination was done at three weeks post-drug administration (21 days), as recommended by the WHO [30]. The poor efficacy of praziquantel against immature parasites has been elucidated as a possible cause of low CRs, especially if the assessment of drug efficacy is done > three weeks post-drug administration particularly high transmission areas, where the residents are continuously exposed for new infections and harbor more immature parasites [16]. A recent study conducted in north-western Tanzania, where the assessment was done eight weeks post-treatment, reported a lower CR, i.e., 68.68% [31]. Similar low CR (60.9%) and ERR (61.4%) were reported from Côte d'Ivoire at six weeks post-treatment [25]. The poor efficacy of praziquantel against juvenile schistosomes is well recognized, and hence, the need for further treatment optimization research is evident. To enhance praziquantel performance, randomized clinical trials (RCTs) to investigate the combination of praziquantel with other drugs that are active against the juvenile worms (such as artemisinins) [32], or the use of repeated praziquantel doses, may be considered in endemic settings [16,31].
On the other hand, praziquantel at a single dose of 40 mg/kg body weight continues to be a safe and tolerable drug among infected school children, as observed in this study. Only 28.7% of the study participants experienced treatment-associated adverse events within four hours of praziquantel administration. Furthermore, in this study, almost all of the observed adverse events among the study participants were mild and transient, similar to reports from other studies [19][20][21]25], and no serious adverse events were reported. Praziquantel is reported to be associated with gastrointestinal symptoms (such as abdominal pain, nausea, vomiting, and diarrhea), neurological symptoms (including headache, muscle pain, drowsiness, dizziness, and fainting), and dermatological symptoms (such as itching, skin rashes) [33].
The type and severity of the adverse events mainly depend on pre-treatment infection intensity and feeding status of the children before drug administration. As recommended by the WHO [30], the provision of meals before drug administration may help to reduce the nauseating effect of the drug, and hence, also to reduce the occurrence and severity of treatment-associated adverse events. In this study, abdominal pain was the most observed adverse event (26.7%). A similar finding is reported from other previous studies [19][20][21]25]. The abdominal pain was significantly associated with pre-treatment infection intensity of the study participants, similar to what was reported in other studies [21]. Children with moderate to heavy infections experienced more abdominal pain compared to those with light infections. On the other hand, vomiting was significantly associated with anemia in the studied population. Participants who were anemic experienced vomiting more than those without anemia. This finding is important, especially in settings like the Lake Zone in Tanzania, where a significant percentage of children have been reported to be anemic [7,28]. The national NTD control program should consider assessing children for anemia (e.g., by physical examination) prior to mass praziquantel administration. Our study observed few adverse events (abdominal pain and vomiting only) compared to other studies, where adverse events like drowsiness, dizziness, muscle pain, fatigue, and weakness were also reported [21,22,33]. The difference can be attributed to study population differences, including genetics, feeding status before drug administration, nutritional status, and disease prevalence and intensity in a given region [34][35][36]. In these circumstances, where treatment-associated adverse events are dependent on pre-treatment infection intensity and anemia status, safety monitoring in the mass praziquantel administration to school children in endemic settings remains crucial.

Study Area
The study was conducted in Nyamikoma village, Busega district, north-western Tanzania between May 2017 and January 2018 in collaboration with the National Institute for Medical Research (NIMR), Mwanza Research Centre Tanzania. Nyamikoma village is located approximately one kilometer from the Lake Victoria basin; it is one of the endemic settings in Busega district. Busega district is one of the administrative districts in Simiyu region; it borders the Lake Victoria to the North. Schistosomiasis is among the top 10 diseases of public health importance in the district. The main economic activities around the district include fishing in Lake Victoria and farming of both animal husbandry and crops. The lake is the main source of water for all human needs in the village and school.

Study Design and Population
This was an observational prospective safety and efficacy surveillance study of praziquantel in Schistosoma mansoni infected school children. The efficacy of praziquantel was measured at three weeks post-treatment (21 days) and treatment-associated adverse events were monitored within four hours of post-treatment. A total of 341 school children (aged 7-17 years) infected with intestinal schistosomiasis residing in Nyamikoma village were enrolled in the study.

Data Collection Procedures
Sociodemographic data including age (school registry), gender, and clinical data such as pre-treatment presenting symptoms, hemoglobin (Hb) concentration, anthropometric measurements (body weight and height), egg count, and observed treatment-associated adverse events from each participant were collected using the case record form prepared for the study.

Stool Sample Examination: Field and Laboratory Procedures
Two fresh stool samples were collected on two consecutive days, both at the baseline survey (pre-treatment) and three weeks post-treatment for screening (diagnosis), and the assessment of drug efficacy (CR and ERR), respectively. Four thick Kato Katz smears were prepared using a 41.7 mg template [37] in a temporary field laboratory by experienced field technicians from NIMR Mwanza Research Centre. The thick Kato Katz smears were transported to NIMR Mwanza Research Centre laboratory and examined by two trained and experienced technicians. To ensure the clear visibility of Schistosoma eggs, microscopic examination of the smears was done 24 h after the preparation of the slides to allow adequate coloration of the eggs by the stain (methylene blue). About 10% of the smears were subjected to quality control by an external technician. The mean egg count of each participant was calculated as an average of the four prepared thick Kato Katz slides. S. mansoni infection intensity described as eggs per gram of stool (epg) was calculated by multiplying the mean egg count by a constant factor of 24 [38], and classified according to the WHO classification; (i) light infection (epg < 100), (ii) moderate infection (epg 100-399), and (iii) heavy infection (epg ≥ 400) [39]. Examination of the parasitological CR and ERR was conducted three weeks after drug administration (21 days), as recommended by the WHO [30].

Estimation of Hemoglobin Concentration and Anthropometric Measurements
Before praziquantel administration, finger-prick blood (100 µL) was collected to measure hemoglobin concentration (Hb conc) in g/dL using the HemoCue Hb 201+ analyzer (HemoCue AB Angelholm, Sweden) [40]. A child was defined as anemic if the Hb conc was less than 11.5 g/dL [41]. Anthropometric measurements were used to assess the nutritional status of the children. Bodyweight was measured in kilograms (kg), and height was measured in centimeter (cm). Body mass index (BMI) was calculated as a ratio of body weight (in kg) to height square (in meters). To assess for stunting and wasting, the anthropometry were converted to Z scores as height for age Z score (HAZ) and body mass index (BMI) for age Z score (BAZ) using the WHO Anthro-Plus software version 1.0.4 (Department of Nutrition, WHO, Avenue Appie, Geneva, Switzerland) [42]. All children with HAZ and BAZ scores less than two standard deviations were considered stunted and wasted, respectively.

Drug Administration and Safety Assessment
The praziquantel tablets used in this study were obtained as a donation from the Tanzania NTD control program. The Tanzania NTD control program receives praziquantel tablets from the WHO. Before drug administration, study participants were given a standardized meal (porridge and biscuits) to minimize the nauseating effect of praziquantel. Thereafter, a single dose of 40 mg/kg body weight of praziquantel (Batch BZ6043, S Kant Health Care Ltd, India) was administered to each study participant as recommended by the WHO for the treatment of schistosomiasis [30]. Following drug administration, study participants were closely monitored for any treatment-associated adverse events including gastrointestinal, neurological, and dermatological symptoms presenting within four hours of drug administration, as described previously [21][22][23][24].

Study Outcomes
The primary outcome of the study was efficacy (CR and ERR) based on the thick smear Kato-Katz method at three weeks post-treatment. The CR was defined as the proportion of egg positive (infected) children before treatment who became egg negative (eggs free) at three weeks post-treatment. The ERR was calculated as 100 times [1 − (Arithmetic mean of epg after treatment/Arithmetic mean of epg before treatment)], as recommended by the WHO [30]. Secondary outcome was treatment-associated adverse events presented or reported within four hours of drug administration.

Data Management and Statistical Analysis
All data were handled by the Data Management Unit (DMU) of NIMR Mwanza Research Centre. Data were double entered in a database (Census and Survey Processing System (CSPro) software (US Census Bureau, Washington, DC, USA), cleaned, and then exported into an excel file. Data analysis was done using Statistical Package for Social Sciences (SPSS) software for Windows version 20 (SPSS, IBM Corp, Armonk, NY, USA). Descriptive statistics were used to analyze the socio-demographic data, baseline characteristics, and results summarized in frequency tables. Depending on the test appropriateness, a Pearson's chi-square test or Fisher's exact test was used to compare proportions between groups. A Mann Whitney U test was used to compare means of the egg count at baseline and at the follow up visit between groups. Univariate and multivariate regression analyses were used to determine the predictors of cure. Variables with p-value < 0.3 on univariate analysis were included in the multivariate regression model. Statistical significance was considered at a p-value of < 0.05.

Conclusions
Praziquantel given as a single dose (40 mg/kg body weight) is still efficacious and safe against Schistosoma mansoni infection, as per the WHO guideline. The drug can still be used in MDA by the national NTD programs among school children and other at-risk populations. However, the failure to cure in one-fifth (18.8%) and adverse events in more than a quarter (28.7%) of the infected children indicate the need for regular and close monitoring of the safety and efficacy of the drug, especially in areas of high transmission in endemic settings. Further studies to optimize praziquantel safety and performance are worth exploring to achieve schistosomiasis control and eventual elimination.