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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Intestinal Nematodes

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Enterobius vermicularis ( Pinworm ) : Parasitology

The adult female is a 10-mm-long, cream-colored worm with a sharply pointed tail, character-istics that have given rise to the common name pinworm.

PARASITES AND DISEASES

Enterobius

Enterobius vermicularis  ( PINWORM ) : PARASITOLOGY

The adult female is a 10-mm-long, cream-colored worm with a sharply pointed tail, character-istics that have given rise to the common name pinworm. Running longitudinally down bothsides of the body are small ridges that widen anteriorly to fin-like alae. The seldom-seen male is smaller (3 mm) and possesses a ventrally curved tail and copulatory spicule. The clear, thin-shelled, ovoid eggs are flattened on one side and measure 25 by 50μm (Fig 55 – 1).



LIFE CYCLE

The adult worms lie attached to the mucosa of the cecum. As its period of gravidity draws to a close, the female migrates down the colon, slips unobserved through the anal canal in the dark of the night, and deposits as many as 20,000 sticky eggs on the host’s perianal skin, bedclothes, and linens. The eggs are near maturity at the time of deposition and become infectious shortly thereafter. Handling of bedclothes or scratching of the perianal area to relieve the associated itching results in adhesion of the eggs to the fingers and subsequent transfer to the oral cavity during eating or other finger – mouth maneuvers. Al-ternatively, the eggs may be shaken into the air (eg, during making of the bed), inhaled, and swallowed. The eggs subsequently hatch in the upper intestine and the larvae migrate to the cecum, maturing to adults and mating in the process. The entire adult-to-adult cycle is completed in 2 weeks.


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