The WHO estimates that almost 2 billion people are infected with one or more of these soil transmitted helminths, accounting for up to 40% of the global morbidity from infectious diseases, excluding malaria. Out of these, approximately 300 million infections result in severe morbidity, which are associated with the heaviest worm burdens. In recent years much new information has been obtained about the epidemiology, population biology and public health signifcance of infections of intestinal helminths in humans.