This study will recruit 350 helminth-infected and 350 helminth-uninfected children aged 6-15 years. Recruited children will be randomized to receive either anthelmintic or placebo treatment once every three months and will be monitored for incidences of diarrheal disease for 12 months. At the 12-month time point, all children will receive anthelmintic treatment. Blood and stool samples will be collected throughout the study and used for evaluation of anemia and host immune responses, and for classification of gut microbes and parasite detection, respectively. The interventional study proposed here will provide an important first test of whether anthelmintic treatments have any indirect effects on infections caused by diarrheal pathogens.