MODEL RELEASEDO. Child with threadworms. A young boy wearing pyjamas scratches his anus to relieve the symptoms of threadworm infection (enterobias- is). He is standing in his bedroom reading a book. Enterobiasis is caused by parasitic nematode worms of the genus Enterobius. The adult worms inhabit the large intestine, where they grow to about 12mm long. They pass out of the anus at night-time to lay eggs in the skin around the anus, causing itching. The infective eggs are transferred to the fingers by scratching, from where they can spread to other children. Enterobiasis is very common, affecting 1 in 5 children in temperate countries. Treatment includes drugs, ointments and hygiene.