Enterobius vermicularis

Enterobius vermicularis is a Nematode that is the causative agent of pinworm infections, oxyuriasis, or enterobiasis. The parasite worm also goes by the name “pinworm”. It is one of the most common nematode infection, especially in young children. It is also a commonly seen infection in institutions where there is overcrowding such as extended care facilities and prisons.

Disease / Pathogenesis

Enterobius vermicularis will cause itching of the rectal / anal area leading to (because of the nocturnal behavior of the female) insomnia , restlessness, and irritability in children. There can also occur abdominal pain and nausea that is intermittent. In females the worms may migrate to the vaginal area to deposit eggs and cause vaginitis.

Symptoms of appendicitis can occur due to the worm inhabiting the appendix of the host.

Secondary bacterial infections can occur due to the intense itching by the host of the affected area.

Location in the Host

Enterobius vermicularis is located in the host cecum, rectum, colon, rectum, and can interestingly enough become an inhabitant of the appendix.

Geographic Distribution

Enterobius vermicularis is found to have a worldwide distribution.

Life Cycle

Morphology & Diagnosis

Enterobius vermicularis eggs are diagnostic and can be found in the rectal / anal surface where the they are deposited by females nocturnally. The tape prep technique is the most commonly used technique to detect the presence of the eggs. Eggs are very rarely seen in the stool or ova & parasite examination. Worms can sometimes be seen on the surface of feces in heavy infections and resemble small pieces of creamy white thread.

This nocturnal movement of the female worms to the rectal / anal area produces irritation leading to sometimes intense itching by the host of the area. This can lead to restlessness and sleep deprivation especially in children whom are most commonly infected with this parasite. Because of the sleep deprivation these children are many times restless or cranky during the day and may develop problems in school.

Worm infections by children are thought to be more common due to the habit of children playing in infected dirt and later placing their hands in their mouth. The eggs are very environmentally resilient.

Infections are difficult to eradicate at times due to the infectivity of the worms and all members of the household may require treatment because child whom is infected will have transmitted the parasite to other household members unwittingly. This is due to the large number of eggs that may be dispersed; their resiliency; and the ability of the eggs to become airborne. As an example, bed sheets need to be collected and carefully without shaking so as to prevent the introduction of eggs into the air. Bed sheets then need to be washed in hot water. Family members may have to undergo multiple treatments and the house may have to undergo significant cleaning / disinfection in order to clear the infection from all family members.


Enterobius vermicularis in section of colon – cross-section of worm – photo by W. Vientos
Enterobius vermicularis gravid female – note the numerous eggs from mid to down of photo. Photo by W. Vientos

Right Image – Enterobius vermicularis eggs on a tape prep. Note translucent eggs at 10 and 5 with characteristic flattened sides. Left Image – Enterobius vermicularis eggs under oil immersion and stained with Lugol’s Iodine. The eggs were obtained from a gravid female worm pulled from the surface of a stool