Mass drug administration significantly reduces infection of Schistosoma mansoni and hookworm in school children in the national control program in Sierra Leone

A National Neglected Tropical Disease Control Program (NTDCP) was established in Sierra Leone by the Ministry of Health and Sanitation in 2008 to target onchocerciasis, lymphatic filariasis, schistosomiasis, STH and trachoma. It was based upon the existing Community Directed Treatment with Ivermectin (CDTI) platform developed for onchocerciasis control [23]. As part of the integrated effort for NTD control, national mapping of schistosomaisis and STH was conducted in 2008 [15] and a complementary survey in 6 highly endemic districts in 2009 [16]. Following the mapping, MDA activities were planned by the NTDCP. Considering the high prevalence of schistosomiasis in many districts and the first ever large-scale praziquantel distribution in the country, the MDA was started in a carefully planned, phased manner. The first phase targeted only school-going children in all primary schools in six highly or moderately endemic districts in June 2009 through school-based drug delivery. To minimize the side-effects of praziquantel treatment in this first-ever MDA, a special school feeding program for children to be treated was arranged with the support of USAID, as in rural settings in Sierra Leone, many children go to school in the morning without a meal and some may not have eaten the night before. The health workers were trained not to give praziquantel to any child with a history of convulsions during MDA. Supplies of anti-histamines and paracetamol were donated to the NTDCP by the St Andrews Clinic for Children-SL a local NGO, for distribution by health staff to children if any mild side-effects might occur. A total of 562,980 school children were treated with praziquantel and 549,701 were also treated with mebendazole with reported coverage of 94% and 92% respectively in this first round of MDA [23].

From the mapping in 2008 and the complementary survey in 2009, fifteen (15) schools shown to have high prevalence of schistosomaisis (≥ 50%) and moderate or high prevalence of hookworm (≥ 20%) were selected as sentinel sites from Bo (Southern Province), Kailahun, Kenema and Kono (Eastern Province), Tonkolili and Koinadugu (Northern Province). Data collection for pre-MDA was already described previously [15, 16]. Briefly, a single stool sample was collected from each participant and one slide per sample was prepared and examined using the Kato-Katz method by experienced examiners.

Six months after the treatment with praziquantel and mebendazole a cross-sectional survey was conducted in the selected sentinel schools. After sensitization of the community and school teachers approximately 30 children aged 9-14 years were randomly sampled in each site without discrimination by gender, religion or ethnicity. A single stool sample was collected from each participant, labelled and preserved in 10% formalin as did previously [16]. Participants were given albendazole 400 mg after the collection of specimens. The samples were transported back and later examined in the Njala University laboratory using the Kato-Katz method using a 41.7 um template (Vestergard Asia, PVT Ltd, India). One slide per sample was prepared and examined by experienced examiners. S. mansoni and STH eggs were counted and intensity of individual infections were calculated and expressed as eggs per gram of faeces (epg). Infections in children were classified as low, moderate or heavy infections according to the intensity of infection based upon the World Health Organization classifications [24].

Results obtained were entered into Epi info^® version 3.5.1 and exported into SPSS 19.0 for analysis. For data from the surveys before MDA only those children aged 9-14 years were included in the current analysis. Analysis was done using SPSS Complex Samples (districts as strata and schools as clusters). Samples in each school were weighted according to the standard sample size (30). Chi square test was used to compare the prevalence before and after MDA. Kruskal Wallis test was used to compare the intensity of infection before and after MDA. The 95% confidence intervals (CIs) for prevalence were calculated using the Wilson score method without continuity correction after adjusting for sample weighting [25]. GPS coordinates were recorded and ArcMap 9.2 software was used to plot school locations.

Ethical approval for the survey was obtained from the Ministry of Health and Sanitation, Sierra Leone and the Liverpool School of Tropical Medicine Research Ethics Committee. Community informed consent was obtained following discussion with District Medical Officers, Chiefdom school inspectors, head teachers and community-teachers associations. Individual verbal consent was obtained from parents or carers as literacy rates among parents were low in most of these locations.

The overall prevalence of S. mansoni infection in school children aged 9-14 years in these sentinel sites was 69.0% (95% CI: 64.7-73.2%) before MDA and it was 38.2% (95% CI: 33.8-42.8%) 6 months after MDA as shown in Table 1 and illustrated in Figure 1. This represents a significant reduction of 44.6% in prevalence after a single dose of praziquantel (p < 0.001). The overall intensity of S. mansoni infection was 170.8 epg (95% CI: 84.2-257.3 epg) before MDA and it was 47.3 epg (95% CI: 11.2-83.4 epg) 6 months after MDA. This represents a significant reduction of 72.3% from moderate to low mean intensity of infection (p < 0.001). Most importantly, the proportion of moderately and heavily infected children decreased from over 35.6% to 9.9% (Table 2).

Both prevalence and intensity of S. mansoni infection showed noticeable reduction across the districts surveyed after a single praziquantel MDA, with reduction rate ranging from 32.8% to 62.3% and 58.8-82.2% respectively. Among 15 sentinel schools, only four (4) schools still showed S. mansoni prevalence of over 50% after MDA, compared with 13 schools before MDA (details not shown). There was no significant difference in the of S. mansoni infection reduction by sex.

The main STHs found in the surveys were hookworms, A. lumbricoides and T. trichiura. The overall prevalence of hookworm infection before MDA was 41.7% (95% CI: 37.3-46.4%), and it was 14.5% (95% CI: 11.6-18.1%) 6 months after MDA as shown in Table 1 and illustrated in Figure 1. This represents a significant reduction of 65.2% in prevalence (p < 0.001). The overall intensity of hookworm infection was 71.7 epg (95% CI: 44.1-99.3 epg) before MDA, and it was 8.7 epg (95% CI: 3.5-14.0 epg) 6 months after MDA, representing a significant reduction of 87.9% (p < 0.001). Such reduction in intensity of infection was seen across the districts surveyed. Among 15 sentinel schools, none of the schools showed prevalence of hookworm infection of over 50% after MDA, compared with 6 schools before MDA (details not shown).

As previously reported [15], the overall prevalence and intensity of A. lumbricoides and T. trichiura infections were low before MDA at 1.8% (95% CI: 1.0-3.5%) and 3.8% (95% CI: 2.4-5.9%) and 7.1% (95% CI: 5.2-9.8%) and 2.1% (95% CI: 1.1-3.8%) 6 months after MDA respectively. The overall intensity of A. lumbricoides and T. trichiura infections was 7.3 epg (95% CI: 0-15.7 epg) and 12.1 epg (95% CI: 0-27.6) before MDA, and was 6.0 epg (95% CI: 0-13.8 epg) and 1.2 epg (95% CI: 0-2.8 epg), respectively. Further analysis was not performed. There was no significant difference in the of Hookworm infection reduction by sex.

Despite the protocols in place of feeding children before praziquantel treatment, as many as 30% of children in some schools were feeling unwell following treatment, mostly with abdominal pain, nausea, vomiting, diarrhoea and dizziness (Turay, unpublished data). These were self limiting or responded to the donated drugs provided with only one case requiring an intravenous infusion and one case of convulsion though it was not clinically confirmed to be due to praziquantel treatment (NTDCP report).

The total additional cost of delivering MDA in 2009 was 169,010 US dollars excluding the salaries from the Ministry of Health and Sanitation, logistic, drug supplies and infrastructure or 0.15 US dollars per child treated against schistosomiasis and STH. The total cost of performing the post MDA survey was 9,900 US dollars ($4.3 per child) including the costs of surveying 504 pre-school children aged 4-5 years old reported separately. In addition the costs of providing drugs to treat common side effects: paracetamol, oral rehydration salts and anti-histamines (donated) were estimated as 3,000 US dollars.