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Enterobiasis

[Enterobius vermicularis]

Cross-section of a male E. vermicularis from tissue, stained with H&E. Notice the presence of the alae (blue arrow), intestine (red arrow) and testis (black arrow).
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Cross-section of a male E. vermicularis from tissue, stained with H&E. Notice the presence of the alae (blue arrow), intestine (red arrow) and testis (black arrow).


Adult male of E. vermicularis from a formalin-ethyl acetate (FEA) concentrated stool smear. The worm measured 1.4 mm in length. Image contributed by the Centre for Tropical Medicine and Imported Infectious Diseases, Bergen, Norway.

Adult male of E. vermicularis from a formalin-ethyl acetate (FEA) concentrated stool smear. The worm measured 1.4 mm in length. Image contributed by the Centre for Tropical Medicine and Imported Infectious Diseases, Bergen, Norway.


Eggs of E. vermicularis in a wet mount.

Eggs of E. vermicularis in a wet mount.

Causal Agents

The nematode (roundworm) Enterobius vermicularis (previously Oxyuris vermicularis) also called human pinworm. (Adult females: 8 to 13 mm, adult male: 2 to 5 mm.) Humans are considered to be the only hosts of E. vermicularis. A second species, Enterobius gregorii, has been described and reported from Europe, Africa, and Asia. For all practical purposes, the morphology, life cycle, clinical presentation, and treatment of E. gregorii is identical to E. vermicularis.


Life Cycle

Life cycle of Enterobiasis

Eggs are deposited on perianal foldsThe Number 1. Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal areaThe Number 2. Person-to-person transmission can also occur through handling of contaminated clothes or bed linens. Enterobiasis may also be acquired through surfaces in the environment that are contaminated with pinworm eggs (e.g., curtains, carpeting). Some small number of eggs may become airborne and inhaled. These would be swallowed and follow the same development as ingested eggs. Following ingestion of infective eggs, the larvae hatch in the small intestineThe Number 3 and the adults establish themselves in the colonThe Number 4. The time interval from ingestion of infective eggs to oviposition by the adult females is about one month. The life span of the adults is about two months. Gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal areaThe Number 5. The larvae contained inside the eggs develop (the eggs become infective) in 4 to 6 hours under optimal conditionsThe Number 1. Retroinfection, or the migration of newly hatched larvae from the anal skin back into the rectum, may occur but the frequency with which this happens is unknown.

Geographic Distribution

Worldwide, with infections more frequent in school- or preschool-children and in crowded conditions. Enterobiasis appears to be more common in temperate than tropical countries. The most common helminthic infection in the United States (an estimated 40 million persons infected).

Clinical Presentation

Enterobiasis is frequently asymptomatic. The most typical symptom is perianal pruritus, especially at night, which may lead to excoriations and bacterial superinfection. Occasionally, invasion of the female genital tract with vulvovaginitis and pelvic or peritoneal granulomas can occur. Other symptoms include anorexia, irritability, and abdominal pain.

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
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