Enterobiasis pathophysiology

Template:Pinworm Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Pathophysiology

The image shown below depicts the life cycle of the pinworm.

Forms of Worm

The best known is the human pinworm Enterobius vermicularis and the more recently discovered Enterobius gregorii. The adult pinworm 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 pinworm is commonly found in children, but adults may also be affected.

Habitat

The pinworm lives in the large intestine and cecum. It is found worldwide, and causes the most common infection enterobiasis in humans. Unlike many other intestinal parasites, the pinworm does not usually enter the bloodstream or any other organs besides the intestines. Only in rare cases pinworms are found in the vagina, and even more rarely in the uterus, fallopian tubes, liver, and peritoneum, but the worms cannot survive long in these places.

The human pinworm 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. Samples of Caucasian children in the U.S.A. and Canada have shown incidences of infection of between 30% to 80%, with similar levels in Europe.

Reproduction

After mating, the male 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 cloth, toys, and the bathtub. Once ingested orally, the larvae hatch in the small intestine specifically the duodenum and migrate back to the large intestine where they mature, maturity is reached 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.

Mode of Transmission

Pinworm eggs spread directly from person to person. They can also be spread by touching bedding, food, or other items contaminated with the eggs. Typically, children are infected by unknowingly touching pinworm eggs and putting their fingers in their mouths. The eggs are swallowed, and eventually hatch in the small intestine. The worms mature in the colon. Female worms then move to the child's anal area, especially at night, and deposit more eggs. This may cause intense itching. The area may even become infected. The itching will often lead to re-infection as the eggs are captured under the fingernails, and eventually reintroduced orally. The eggs can also be spread by air and other mechanisms eventually leading to oral introduction into the victim.

Microscopic Pathology

Histopathology of appendix showing pinworms {{#ev:youtube|PkemlmA_tf0}}