Ecological and Physicochemical Determinants of Freshwater Snail Prevalence, Density, and Schistosome Infection in the Lango Subregion, Northern Uganda: Implications for Disease Control

Background Freshwater snails serve as intermediate hosts for trematodes that cause human and animal diseases, notably schistosomiasis and fascioliasis. In Uganda’s Lango subregion, schistosomiasis remains endemic, yet the ecological and physicochemical factors influencing snail prevalence, density, and infection remain poorly understood. This study investigated these factors to inform targeted disease control strategies. Methods A cross-sectional study was conducted in the Lira and Kole districts during the dry and rainy seasons of 2023. Snails were collected from streams, ponds, swamps, and rice paddies by handpicking and scooping methods. Morphological identification and cercarial shedding tests were performed to determine the species composition and infection status. Physicochemical water parameters, including pH, salinity, dissolved oxygen (DO₂), total dissolved solids (TDS), and temperature, were measured. Generalized linear models were used to assess the predictors of snail prevalence and density. Results A total of 4,802 snails from 13 species were collected, with Biomphalaria (47.2%) and Bulinus (23.7%) being the most abundant genera. The snail density was greater in the rainy season (53.7%) than in the dry season (46.3%). Among the 3,404 Biomphalaria and Bulinus snails examined, 0.15% were infected with schistosome cercariae, including Biomphalaria sudanica (0.03%), B. choanomphala (0.06%), and Bulinus africanus (0.06%). Logistic regression analysis revealed that salinity, TDS, conductivity, water depth, and DO₂ significantly influenced snail prevalence, explaining 73.1% of the variation in B. sudanica and 82.2% in B. choanomphala . Negative binomial regression (Table 3) indicated that water temperature, TDS, pH, and anthropogenic activities affected snail density. Lymnaea natalensis and B. choanomphala thrived in habitats with moderate DO₂ values and human activities such as washing and bathing, whereas car washing negatively impacted density. Conclusions This study highlights the role of ecological and physicochemical factors in freshwater snail distribution, density, and infection rates. These findings provide critical insights for targeted snail control interventions, including habitat modification, improved sanitation, and seasonal mass drug administration, to mitigate schistosomiasis transmission in the Lango subregion and nationwide.