Enterobius vermicularis - MegaMicro

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Enterobius vermicularis

Microbiology > Parasitology > Nematodes
Structure:  Helminth, nematode: Small, slender white worm.   Adult female 8-13 mm and adult male 2-5 mm in length.

• Infection is initiated by the ingestion of embryonated eggs either directly or indirectly through contact with contaminated objects (clothes, bedding, etc).  Occasionally, eggs may become airborn and inhaled, then swallowed.
• Occurs worldwide (predominately in temperate regions), the most common nematode infection in North America and Western Europe.
• Person-person spread, facilitated by crowded conditions, occurring most often in children, institutionalized persons, household members of individuals with pinworm.
• No animal reservoir

• Following Ingestion of infective eggs, larvae hatch in the small intestine, migrate to the large intestine and mature into adults within 2-4 weeks.
• As many as 20,000 eggs are laid in the perianal folds by migrating female adults (primarily at night).  The eggs mature rapidly and become infectious in 4-6 hours.
• Autoinfection may occur when eggs on the perianal folds mature into adults which migrate back into the intestine via the rectum.

Disease Manifestations:
• Many infections are asymptomatic.
• The most common symptom is perianal itching (pruritus ani) occurring predominately at night.
• Genitourinary symptoms may occur if the adult worm migrates into the vagina.
• Worms in the bowel may result in inflammation and/or granuloma formation around the eggs

Laboratory Diagnosis:
• Detection of eggs on the perianal skin:  Use scotch tape or a commercially available pinworm paddle (both have sticky surfaces) to pick up the eggs from the skin.  Obtain the sample at night or first thing in the morning for the highest yield of eggs.
• Microscopic exam revealing ovoid eggs with one flattened side.
• Adult worms may occasionally be seen in the anal region 2-3 hrs after falling asleep.
• Stool samples are of limited usefulness, as adult worms or eggs are rarely passed in the stool.

Differential Diagnosis:

• Albendazole or mebendazole (1 dose, repeat in 2 weeks to prevent reinfection)
• Pyrantel pamoate, available over the counter (1 dose, repeat in 2 weeks)
• Treat the entire household to avoid reinfection

Prevention and Control:
• Good personal hygiene, clean environment, safe food preparation practices
• Frequent changing of undergarments and bed linens first thing in the morning

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