Intestinal worms infect about 10 per cent of the population in the developing world and, depending upon the severity of the infection, lead to malnutrition, anaemia or retarded growth. Children are particularly susceptible and typically have the largest number of worms. About 400 million school-age children are infected by roundworm, whipworm and/or hookworm. In fact, roundworm and whipworm alone are estimated to affect one-quarter of the world’s population. People become infected with intestinal parasitic worms (also known as helminths) through contact with soil that has been contaminated with human faeces from an infected person, or by eating contaminated food.