Ecology of bulinid snail intermediate hosts and transmission of schistosoma haematobium among school aged children in Shinyanga district, Tanzania

Abstract

This study investigated transmission of Schistosoma haematobium through longitudinal parasitological, malacological and human water contact surveys. Urine samples collected from school children were examined for S. haematobium infection using urine filtration method. Snail samples collected were examined for patent schistosome infections by microscopy. Multiplex PCR assessed pre-patent infections and differentiated S. haematobium from S. bovis. Water contact questionnaire, focus group discussion and semi structured interviews explored community knowledge on schistosomiasis. Pre-treatment prevalence of S. haematobium infection among school children was 34.8%. Prevalence of S. haematobium infection was higher in older children (12–14 years) compared to younger children (6-11 years) (p<0.001) with no significant variation one-year post-treatment. Boys were more infected than girls. No spatial association was observed between children‘s infection and the distance from child‘s home to the nearby snail habitats. Integration of malacological surveys linked with GPS data detected spatial association between children living in households next to ponds with high B. nasutus having the highest prevalence of S. haematobium infection. From 6202 Bulinus nasutus collected, 190 (3.06%) had patent infections. Rainfall pattern had significant impact on snail population density. Water conductivity (OR 1.23; 95%CI 1.131.34;

p<0.0001) and vegetation (OR 6.84; 95%CI 2.75-16.99; P<0.0001) were significantly associated with snail population abundance. Increase of conductivity in snail habitats with vegetation reduced snail densities significantly (OR 0.76; 95%CI 0.68-0.86; P<0.0001). Increase of water temperature was associated with patent infection in pond habitats (OR 0.35; 95%CI 0.45-0.62; P<0.0001) but not rivers. Other physico-chemical parameters were not significantly associated with snail abundance. Out of 1898 B. nasutus snails for which DNA was extracted, 100 (5.17%), 291 (15.07%) and 16 (0.84%) were S. haematobium, S. bovis and S. haematobium/S. bovis co-infected, respectively. Water sources shared between humans and livestock had significantly higher S. haematobium (OR 2.53; 95%CI 1.59-4.05; p<0.0001) and S. bovis (OR 2.29; 95%CI 1.53-3.45; P<0.0001) infections. Wet season was associated with significant reduction of S. bovis infection (OR 0.17; 95%CI 0.09-0.32; P<0.0001). Molecular approach, malacological and a parasitological survey when tied together detect specific schistosome species transmitted. Measures for schistosomiasis control should take into account integrated strategies for disease elimination.