Transmission studies of intestinal schistosomiasis in Lake Albert, Uganda and experimental compatibility of local Biomphalaria spp.

Despite ongoing preventive chemotherapy campaigns, intestinal schistosomiasis is hyper-endemic in shoreline communities living along Lake Albert, Uganda. To provide a deeper insight into the local epidemiology of Schistosoma mansoni, a variety of field-based studies were undertaken focusing upon schistosome-snail interactions and confirmation of transmission foci. Cercarial shedding patterns of field-caught Biomphalaria spp., as identified by morphology, were hourly observed over a ten day period and showed that Biomphalaria stanleyi produced significantly more cercariae than Biomphalaria sudanica. Peak production times in both species were between 12.00 and 14.00h indicating greatest infection risk from lake water exposure is during the early afternoon. Laboratory-bred snails were exposed to locally hatched miracidia and susceptibility of Biomphalaria spp. was confirmed experimentally. Biomphalaria stanleyi was a more permissive host. After ascertaining appropriate conditions for infection of laboratory mice, 28 groups of between 5 and 6 naïve mice were placed in floatation cages at four suspected shoreline transmission sites for a 30 minute period of exposure. Eight weeks later, mice (n=142) were culled and S. mansoni adult worms were retrieved from 10 animals. Taken as a whole, these observations highlight the local importance of B. stanleyi in transmission of intestinal schistosomiasis and clearly demonstrate the risk of infection on the Lake Albert shoreline. To mitigate this risk local environmental modification(s), i.e. improvement in sanitation and hygiene and control of snail populations, is needed to bolster the impact of chemotherapy-based interventions.