Pregnancy (this is a partial exclusion). Pregnant women will participate in the parasitological screening phase of the study. However, because of pregnancy-related effects on the urinary system, their ultrasound examinations will be excluded from the analysis of hydronephrosis. Further, because of potential toxicity of praziquantel (Category B) and its alternative, metrifonate (an anticholinesterase), post-protocol anti-parasitic therapy will be delayed until the mother delivers and has stopped breastfeeding her infant.