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Enterobiasis is caused by the pinworm Enterobius vermicularis, a
strictly human parasite infecting the gastrointestinal tract. Infection occurs
worldwide, and clustering of cases in families is common. Ingested
eggs with first-stage larvae hatch in the duodenum, and the larvae
develop into adults in the cecum, where they mate. The gravid female
detaches from the cecal mucosa and migrates down the large bowel,
usually passing out the anus onto the perianal and perineal skin,
leaving a trail of eggs on the surface of the skin. Yellow-white female
adult pinworms measuring 8 to 13 mm may be seen emerging from the
rectum of infected children, most often around 10 or 11 pm.
In approximately 5% of patients, eggs are deposited in
the bowel and may be found in feces. Generally, the worm dies after
ovipositing is completed, so repeated infections are the result
of autoinfection or reinfection from other environmental sources.
There is no good evidence that retrograde infection occurs.1
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The eggs average 55 μm by 35 μm
and appear flattened on one side and convex on the other. They are
fully mature and infective 3 to 8 hours after being deposited, but
at normal room temperature, less than 10% of eggs live for
48 hours.
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In the United States, infection rates in young school children
vary from 10% to 45%. Infection is unrelated to
poor sanitary facilities or tropical climates. Young girls have
pinworm more frequently than boys of the same age, and whites are
more often infected than African Americans. Infection is most common between
early fall and late spring, perhaps related to transmission in schools.
For unknown reasons, some individuals seem to be predisposed or
vulnerable to reinfection. Unlike soil-transmitted helminths such
as Ascaris, enterobiasis is more common in urban
settings.
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Infection occurs by ingestion of embryonated eggs excreted in
the stool of infected persons and may occur by hand-to-mouth transmission or
by oral contact with infected fomites, such as toys, bedding, or
clothing. The eggs average 55 μm by 35 μm
and appear flattened on one side and convex on the other. They are
fully mature and infective 3 to 8 hours after being deposited, but
at normal room temperature, less than 10% of eggs live
for 48 hours. Ingested eggs with first-stage larvae hatch in the duodenum,
and the larvae develop into adults in the cecum, where they mate.
The gravid female detaches from the cecal mucosa and migrates down
the large bowel, usually passing out the anus onto the perianal
and perineal skin, leaving a trail of eggs on the surface of the
skin. Yellow-white female adult pinworms measuring 8 to 13 mm may
be seen emerging from the rectum of infected children, most often
around 10 or 11 pm. In approximately 5% of patients, eggs
are deposited in the bowel and may be found in feces. Generally,
the worm dies after ovipositing is completed, so repeated infections
are the result of ...