Follow-up Assessment of Change in Soil-transmitted Helminths Infection Intensity in Uganda

The goal of this prospective follow-up study nested within an open-label randomized controlled trial is to investigate the unexpectedly high prevalence of Ascaris lumbricoides infection observed 3-4 months after school-based mass drug administration with ivermectin plus albendazole (IVM-ALB) or albendazole alone (ALB) in Kisoro District, South-Western Uganda. By assessing initial treatment response and subsequent infection dynamics, the study will help clarify whether reduced drug efficacy, suboptimal treatment coverage, reinfection, or a combination of these factors may explain the previous findings. The main questions the study aims to answer are: * How effective are IVM-ALB and ALB against A. lumbricoides at 3 weeks, based on egg reduction and cure rates? * How often do A. lumbricoides and other soil-transmitted helminth infections recur by 3 months? * How effective are the treatments against Trichuris trichiura and hookworm? * What can genetic characterization of Ascaris eggs reveal about parasite populations and potential drug resistance markers? The study will enrol 450 pupils aged 5-14 years from three primary schools, which participated in the previous mass drug administration evaluation. In each school, 150 pupils will be randomly assigned equally to receive a single oral dose of: * ivermectin (200 µg/kg) plus albendazole (400 mg); or * albendazole (400 mg) alone. Each treatment arm will include 225 pupils overall. Children will be included regardless of baseline infection status, following parental/guardian informed consent and child assent. Other pupils will receive routine albendazole under national deworming guidelines. Stool samples will be collected before treatment and at 3 weeks and 3 months. Duplicate Kato-Katz thick smears will quantify A. lumbricoides, T. trichiura and hookworm eggs. The primary outcome is the arithmetic mean egg reduction rate for A. lumbricoides at 3 weeks. Secondary outcomes include cure rates at 3 weeks, reinfection rates at 3 months, egg reduction and cure rates for T. trichiura and hookworm, and genetic characterization of Ascaris populations and potential resistance markers. Adverse events will be recorded through passive safety monitoring.