Threadworms (Enterobius vermicularis) are small worm parasites that infect the intestines of humans.
Threadworms, sometimes known as pinworms, are white and look like a small piece of thread. The adult female worm can be 8-13mm long, and the male worm 2-5mm long. Adult worms live for up to six weeks.
Threadworms do not always cause symptoms, although some people will experience itchiness around their anus and vagina (in females). The itchiness is particularly noticeable at night and can disturb sleep.
See Threadworms - symptoms for more information.
The life cycle of threadworms
Female threadworms lay tiny eggs around the anus and, in females, around the vagina. This usually happens at night, when the infected person is asleep.
When laying eggs, the female worm also secretes a mucus that causes the person to scratch the area. The eggs can then become stuck on the person’s fingertips and under their fingernails. From here, they can be transferred to the mouth or to surfaces and clothes. It is then possible for other people to touch an infected surface and transfer the eggs to their mouth.
Threadworm eggs can survive for up to three weeks before hatching. If they hatch around the anus, they can re-enter the bowel. If the eggs have been swallowed, they will hatch in the intestine. After two weeks, the worms reach adult size and begin to reproduce, starting the cycle again.
See Threadworms - causes for more information.
How common are threadworms?
In the UK, the threadworm is the most common worm parasite that infects children. It is estimated that up to 40% of children under 10 years of age may be infected with threadworms.
Outlook
Threadworms are spread through poor hygiene. Usually, if one member of a household is infected, others will be too. It is therefore necessary to treat the entire household to prevent re-infection. Following strict hygiene measures for up to six weeks can help prevent infections returning.
Treatment for threadworms is available from your GP or from pharmacies. Treatment may not be suitable for everyone, so always follow the manufacturer’s instructions.
See Threadworms - treatment for more information.
Treatment does not kill threadworm eggs. Good hygiene is the only way to prevent eggs from spreading and causing another infection.
Humans are thought to be the only host for threadworms. Animals cannot catch or pass on threadworms, unless the eggs are transported on the animal’s fur after human contact.
