Threadworms & Roundworms

The adult threadworm male is 1-4 mm in length, while the adult female is 8-13 mm and possesses the long, pin-shaped posterior for which the worm is named. The human threadworm is commonly found in children.

The threadworm lives in the lower part of the small intestine and the upper part of the colon. Unlike many other intestinal parasites, the threadworm does not usually enter the bloodstream or any other organs besides the intestines.

The human threadworm Enterobius vermicularis is a ubiquitous parasite of man, it being estimated that over 200 million people are infected annually. It is more common in the temperate regions of Western Europe and North America, (it being relatively rare in the tropics) and is found particularly in children.

After mating, the male threadworm dies. The female migrates to the anus and emerges, usually during the night, to deposit about 10,000 to 20,000 eggs in the perianal area (around the anus). She then secretes a substance which causes a very strong itching sensation, inciting the host to scratch the area and thus transfer some of the eggs to the fingers. Eggs can also be transferred to clothes, toys, and the bath. Once ingested orally, the larvae hatch and migrate back to the intestine, growing to maturity in 30-45 days. The eggs can survive for 2 to 3 weeks on their own outside of the human body. In some cases, the larvae will hatch in the peri-anal area and travel back inside the anus, up the rectum, and back into the intestines where they mature.

Except for itching, threadworm infestation does not usually cause any damage to the body. Sleep disturbance may arise from the itching or crawling sensations.

Diagnosis is often made clinically by observing the female worm (or many worms) in the peri-anal region or in the toilet after a motion.


Anti-threadworm drugs such as Ovex tablets (mebendazole)(for age 2 years and above)and Pripsen sachets (for age 3 months and above) are commonly used to treat threadworms as well as ascaris lumbricoides (the roundworm).  

A precaution is to wash the hands before eating (to prevent any threadworm eggs under fingernails from being ingested) and to wash any area or clothes which have touched or been in the vicinity of the infected areas. Treating the entire family is often necessary for cure.

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This page was last updated: Monday 25 September, 2017