Praziquantel efficacy and post-treatment reinfection and incidence of Schistosoma mansoni among school-aged children in Northern Uganda: a 24-week cohort study in a high transmission focus

Background Human schistosomiasis is a parasitic disease of major public health importance in sub-Saharan Africa. Mass drug administration (MDA) with praziquantel (PZQ) is the cornerstone of schistosomiasis control. However, its effectiveness is challenged by variable cure rates and rapid reinfection. Longitudinal data on reinfection and true incidence, which are critical for refining control strategies, are scarce from high-transmission foci like the Lango sub-region in Northern Uganda. This study assessed the efficacy of PZQ and the 24-week dynamics of reinfection and incidence of Schistosoma mansoni among school-aged children in this endemic area. Methods A 24-week prospective cohort study was conducted among 802 primary school children (aged 5–16 years). At baseline, participants were screened for S. mansoni using the modified Kato-Katz technique and allocated into an infected cohort ( n = 279) and an uninfected cohort ( n = 523). The infected cohort received a single 40 mg/kg PZQ dose, with efficacy (cure rate-CR, egg reduction rate-ERR) assessed at 4 weeks. Treatment failures received a second dose. To measure true incidence, the uninfected cohort was re-screened at 4 weeks to identify and exclude prepatent infections at baseline. Reinfection in cured children and incidence in consistently negative children were assessed at 24 weeks. Results The baseline prevalence was 34.8% (95% CI: 31.5–38.3). After the first PZQ dose, the cure rate was 82.1% (95% CI: 77.0-86.4), and the egg reduction rate was 32.9%. A second dose administered to non-responders achieved a 93.9% cure rate (95% CI: 83.6–97.9). At 24 weeks, the reinfection rate among cured children was 7.7% (95% CI: 4.9–11.8). After excluding prepatent infections (5.9%, 95% CI: 4.1–8.3) detected at 4 weeks, the true incidence of new infections was 5.0% (95% CI: 3.3–7.4) over the 24-week period. Conclusions Praziquantel remains highly effective for treating S. mansoni in northern Uganda, and a second dose is valuable for curing initial treatment failures. However, the considerable burden of infection at baseline, coupled with notable reinfection and incidence rates within six months, signals persistent high transmission. Operationally, annual MDA may be insufficient; we advocate for piloting more frequent treatment (e.g., biannual MDA), integrating test-and-re-treat strategies (with careful cost-effectiveness evaluation), and strengthening complementary WASH and snail control interventions.