Medical information for patients


Threadworm (enterobiasis, pinworm, seatworm or oxyuriasis) is an intestinal infection caused by a tiny worm known as Enterobius vermicularis, which causes an itchy bottom (pruritus ani).


Threadworm infestation is a very common condition and causes itching, but does not usually cause other serious problems.


The cause is a small worm, enterobius vermicularis. The female is about 10mm long, and the male is about 3mm. They live with their heads attached to the lining of the upper end of the large intestine (the caecum, appendix and other nearby parts of the bowel).

At night, the female finds its way to the anus, and lays its eggs on the skin around the anus. Each egg contains an embryo, which quickly becomes an infective larva. Usually the method in which people reinfect themselves is by getting the eggs under the finger nails by scratching, followed by swallowing the eggs while eating, sucking thumbs, biting nails, etc. Occasionally the larvae get straight back in via the anus.

The initial infection presumably comes from picking up the larvae under the nails in dirt and dust.


Intense itching of the bottom or anus draws attention to the problem. Often the parents actually see the tiny worms around their child's anus. Your doctor may ask you to touch a piece of clear sticky tape against the anus to pick up eggs, which can be identified by the laboratory.


Do not panic! Any family can get threadworm. You do not need to rush around doing anything in the middle of the night. Usually it is wise for the whole family to observe the following precautions, and to take the treatment.

The key to treatment is cutting the nails short and attention to regular washing, with scrubbing of finger nails. The life span of the worms is about six weeks, so if reinfection can be prevented, this alone could clear the infection.

The drug most widely recommended is mebendazole, which can be used from very young. There are a number of other drugs which can also be used. Speak to your pharmacist or doctor.


Continued attention to washing hands before eating and keeping the nails short helps.

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