The Problem Intestinal worms and parasites. Schistosomiasis and STH are types of parasitic “worm” infections. They are part of a group called Neglected Tropical Diseases (NTDs) which affect the poorest and most marginalised communities in the world. Schistosomiasis is carried by freshwater snails and is transmitted through contact with contaminated water during everyday activities, such as bathing and washing clothes, where access to clean water is limited. STH is caused by a group of intestinal parasites, and are transmitted by eggs present in human feces, which contaminate the soil in areas where sanitation is poor. The World Health Organization estimates that 206 million people have schistosomiasis and 1.5 billion have STH. These infections can result in anemia, stunted growth, reduced school attendance, impaired cognitive development, reduced worker productivity and internal organ damage.