High level of Schistosoma mansoni infection in pre-school children in Sierra Leone highlights the need in targeting this age group for praziquantel treatment

Background: Schistosomiasis and soil-transmitted helminth (STH) infections are endemic in Sierra Leone. The consequences of these diseases to pre-school children are well understood. The national control program currently does not target this group of children for schistosomiasis, while mass drug administration (MDA) has been performed six monthly for STHs in children 12-59 months of age since 2006.

Methods: To assist the national decision on MDA strategy to control schistosomiasis and STH, three cross-sectional surveys were conducted in pre-school children in 2009-2011 as part of routine surveillance performed in different areas and in different phases of MDA, including known 'Hard to Reach' villages where consistently poor coverage results were seen in recent MDA. Thirty 4-5 year-old children were randomly selected per site and a stool sample from each child was examined by Kato-Katz thick smear. Pooled data were analyzed for schistosomiasis and separate sets of data were presented for STHs. In total 61 sites were surveyed and a total of 1803 children were examined.

Results: The overall prevalence and intensity of Schistosoma mansoni was 11.2% (95% CI 9.7-12.8) and 33.5 epg (95% CI 19.7-47.3). Relatively high level of infection was found in Kono (35.4% and 102.9 epg), Tonkolili (30.4% and 142.3 epg) and Koinadugu (20.8% and 47.0 epg). There were 8.1% of children 4-5 years old moderately or heavily infected with S. mansoni. Overall level of STH infections were generally low, with hookworm 8.4-22.8%, Ascaris lumbricoides 0.2-17.2%, and Trichuris trichiura 0.9-2.6% in three surveys. However, prevalence of hookworm and A. lumbricoides was relatively high in those hard-to-reach villages even two months after MDA.

Conclusions: Relatively high levels of S. mansoni infections were found in children aged 4-5 years old in Sierra Leone, in line with geographical distribution of the disease observed in older children in the country. The results suggest that this group of children should not be neglected further in the schistosomiasis MDA and a global guideline is needed. Overall prevalence of STH infection was relatively low. Although there was no baseline data for direct comparison, it did show a marked reduction in STH infections, compared with historical data. However, relatively higher prevalence in hard-to-reach villages suggests the difficulty and quality of implementing MDA in such difficult locations, and more efforts and perhaps different delivery strategies are needed in these locations to increase the quality of MDA.