Enterobius vermicularis




E. vermicularis is found worldwide but is most common in temperate regions, where person-to-person transmission is greatest in crowded conditions such as daycare centres, school, and mental institutions. An estimated 500 million cases are reported worldwide, and it is the most common helminthic infection in North America.


Classification and Characteristics

E vermicularis is a nematode helminth. They are small, white worms with oval, thin-walled eggs that are 50-60 x 20-30 µm and flattened on one side. (MA: children sit on the eggs, making them flat)


Transmission and Infection

Infection begins by ingesting eggs, usually transferred from hand to mouth. Eggs can survive long periods in the dust over doors, on windowsills, under beds, etc.

Larvae hatch in the small intestine and mature into adults in two to six weeks. Fertilization of the female by the male prduces characteristic asymmetrical eggs, where are laid in the perianal folds by the migrating female. Up to 20,000 may be laid.

Eggs rapidly mature and are infectious within hours.



Clinical Manifesations

Many children and adults show no symptoms, serving only as carriers.

Patients who are allergic to migrating females can experience severe itching, loss of sleep, and fatigue. The puritus can lead to releated scratching, irritation, and further bacterial infection.

Worms attached to the bowel wall can cause inflammation and granuloma formation around the eggs.



Diagnosis of enterobiasis is suggested by clinical manifestations and confirmation of the ingested eggs on the anal mucosa.

Adults worms may occasionally be seen in stool specimens, but the method of choice involved use of an anal swab with a sticky surface. Clear tape may also be used.



Pyrantel pamoate is the drug of choice, with mebendazole as an alternative. It can be wise to treat the family to prevent reinfection. A second course of treatment after 2-4 weeks may also be useful.

Good personal hygeine, clipping of fingernails, thorough washing of bed clothes, and prompt treatment all contribute to control.