"I have a stomach ache. I feel really tired. I don't want to eat." Not what you'd expect to hear coming from an athletic fourth grader. But for Fernanda, a girl living in Jinotepe, Nicaragua, these symptoms' cause afflicts too many kids, too often - intestinal worms.

Fernanda is one of 400 million children around the world at risk of being infected with soil-transmitted helminthes, or STH (meaning roundworms, whipworms and hookworms), caused by a lack of clean water and poor sanitation. Intestinal worms are especially harmful to children because they can stunt growth and cognitive development, and lead to malnutrition and anemia.