Infestation with nematode worms of the genus Trichuris. They are 3-5 cm long and have a very thin front portion and a fat rear one containing the reproductive organs. They live for roughly eight years. The worms occur throughout the world: approximately 350 million people are infested. At the junction of the large and small intestine the worms probably feed on the contents of the intestine and tissue fluid. They drill their thin section into the intestine wall, while the thick section is free and lays eggs which are then discharged in faeces and develop on the ground. Man can be infested by eating unwashed green vegetables or fruit covered with eggs. The larva hatch in the intestine and develop into fully-grown worms. Discomfort is caused only in cases of secondary infection or when there are large numbers of worms, causing stomach ache, diarrhoea and blood and mucus in the faeces. Treatment is not usually necessary, and contamination can be avoided by thoroughly washing fruit and vegetables.