Authors

Discussion

Background: Hotspots of schistosomiasis persist in Uganda and other sub-Saharan African countries despite nearly two decades of preventive chemotherapy through mass drug administration (MDA). Although praziquantel is donated for free and recommended for community-wide treatment in high endemic areas, coverage remains low and global supplies are limited. A key question is how to optimize drug distribution to maximise success, reduce transmission and minimize heavy infection intensities.

Methods: We conducted a longitudinal survey of 640 individuals aged nine months to 80 years old residing in Bugoto, Mayuge District, Uganda, a high endemic Schistosoma mansoni community. Stool samples were collected for Kato-Katz and isolation of miracidia for population genetic analyses. Reinfection and parasite genetic diversity was re-evaluated at five and 18 months after treatment and compared between age groups, alongside travel survey data.

Findings: Following national MDA, infection intensities were higher in preschool-aged children (PSAC) and young adults compared to SAC. High infection intensities were associated with water contact frequency and duration, ineligibility for MDA, and young adults systematically not offered treatment. Following observed treatment, SAC had the highest reinfection rates. Examination of parasite genetic structure revealed significant differentiation between age groups but not across timepoints. While SAC are often the focus of control programs, we provide epidemiological and genetic evidence that these target groups can be rapidly re-infected by an untreated reservoir of high-risk PSAC and mobile adults importing parasites.

Interpretation: Improving praziquantel treatment coverage in age groups beyond SAC will help high endemic regions reach targets for elimination of schistosomiasis as a public-health burden.