In this study, the overall prevalence of S. mansoni infection among the school children was 35.7%. This is categorized as moderate risk . This prevalence is low compared to those obtained from western Kenya (76.8%), and in Tanzania (64.3%) [24, 25]. This low prevalence in Lira district could be due to the massive administration of preventive chemotherapeutic praziquantel (in Aromo subcounty only) and Albendazole to the school children by MOH Uganda two years prior to the study. This finding is similar with results from studies conducted among communities in islands of Lake Victoria, Uganda [20,21] and in Northwest Ethiopia [22, 23], respectively. Nevertheless, the prevalence obtained in this study is higher compared to 20.1%, 4.6%, 4.3% reported in Gulu municipality, Uganda  and in Jos  and Babile town, Nigeria , respectively. This could be attributed to geographical locations and difference in control interventions.
The prevalence of S. mansoni infection varied significantly with sub-county location and primary schools. Highest infections were recorded in Ogur sub-county and in Akangi and Akano primary schools (both in Ogur subcounty). This could be attributed to the numerous swamps around Ogur sub-county which contains a lot of infected snails (Byagamy pers. obs), and the absence of praziquantel treatment intervention in the area. Ogur subcounty was considered by MOH as a low prevalence area and MDA was administered only in Aromo subcounty. Similar variation in infection prevalence of S. mansoni by geographical location has been reported in previous studies in Gulu, northern Uganda , which have been attributed to variation in intensity of parasite transmission and frequency of exposure to cercariae contaminated water bodies .
Children aged 10-14 years were more infected (52.6%) than children aged 6-9 years (16.3%) with a decline among 15-16 years (31.6%). Studies conducted elsewhere have reported similar results, for example, in Jos, Nigeria, children aged 10-14 years were more infected with intestinal schistosomes (11.1%) than those in other age groups . Similarly, in Gadabuke district, north central Nigeria, those aged 8-14 years was more infected (62.8%) than < 8 years . However, in contrast to the present results, highest prevalence was found among the 6-10 years old (90.4%) in Ethiopia than in those 11-15 years 89.7% . This might be attributed to the behavioral patterns of different age groups with respect to water contact activities and poor personal hygiene. Children aged 10-14 years were older and often got in contact with infected water bodies through various water activities such as swimming, fetching water, playing with shallow water and fishing, washing clothes and farming. However, children older than 14 years have lower risk of being infected as they are less likely to be engaged in recreational water-contact behaviors compared to younger children. Other studies have indicated that age acquired immunity to reinfection contributes to the drop in the prevalence rates among children aged 15 years and above .
Even though some studies reported that prevalence among males was higher than females [30, 31], in the present study no difference was observed in the prevalence between males and females. This could be due to the socio-cultural set-up activities where both males and females are equally actively involved in water-related activities like swimming, fishing, grazing in the swamps, bathing and playing with shallow water, collecting rids from swamps and farming . In Los, Nigeria, for example, prevalence of S. mansoni infections were higher in males (22.2%) than in females (3.7%) [31,36,37]. Another report of higher prevalence rate in boys was given in Gulu municipality, Uganda (boys: 65.2%; girls: 34.8% . The results of this survey further contradicted the findings at Northwest Ethiopia (boys:33.7%; girls: 42.2%)  and in Tanzania (boys 61.65%; girls 65.80%)  which could be due to different geographical locations and socio-cultural factors in those communities.
The high infection rate among children who collect water from the spring (44.7%) compared to those who fetch water from other sources could be because spring is an open source that is prone to contamination with feaces containing eggs of schistosomes. This finding is in agreement with several previous studies [33,31,34]. Fishing and swimming keep children in water for a prolonged time, which increases the chances of cercarial skin penetration.
Finally, the findings in this study have shown that almost 5.3% of the S. mansoni infections are heavy intensity infections and approximately 68.9% are of moderate intensity. This finding is higher than the one in Gulu Municipality which showed only 20.1% moderate infection . This difference may be due to repeated exposure of school children to water bodies infested with infective stage in Lira district. Additionally, children aged 14-16 and 10-14 years had heavy infections compared to their younger counterparts (6-9). This might be due to the fact that older children frequently go to the open water sources to play and fetch water as reported elsewhere . These children spend more time in the infested waters compared to their younger ones, thus increasing the exposure time for infection of S. mansoni.
Overall, this study showed that Lira District is endemic for S.mansoni. Therefore, there’s urgent need for provision of safe water, periodic treatment of all school-aged children with Praziquantel and public health education to reduce the prevalence of S. mansoni.