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Enterobiasis is
a very common parasitic disease of cosmopolitan distribution.
The
causative nematode is E. vermicularis, formerly known as
Oxyuris vermicularis, or commonly as the pinworm or threadworm.
The
disease is acquired by ingestion of fully embryonated ova deposited by
the female worm about the anus and transferred to other hosts by faecal
contamination or to the same host to produce reinfection.
The ova are
very resistant to destruction , and the infection occasionally affects
all persons in the same household.
The life span of the worm is short (1.5
to 2 months), and the main problem is reinfection.
The larvae
are hatched from the fully embryonated ova on the region of the
duodenum and then pass downward while they molt twice and mature,
until they reach the ileocecal area.
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The adult worms attach themselves
to the superficial portion of the mucosa of the terminal ileum, caecum,
and appendix by their anterior end.
The pathologic
changes produced by the adult worms in this area are minimal, and
their role in the pathogenesis of appendicular symptoms in some cases
is
not clear.
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The general
impression is that, even when adult worms are present in acute
appendicitis, they are not a significant cause of inflammation.
The most
important symptoms of the disease is intense pruritus ani caused by
the migration of the adult female worm to the perianal region, when
she lays her eggs.
The adult male worm is unimportant in
the pathogenesis, since it dies after copulation.
Rarely, E. vermicularis can be seen in extraintestinal sites.
In female the
nematode migrates up the uterus and fallopian tubes to produce a
foreign-body type of granulomatous inflammation most commonly seen in
the surface of the ovaries, omentum, and peritoneum.
This parasite
apparently cannot survive outside its normal habitat, and the granulomatous reaction described occurs after death of the worms.
Other less
common ectopic sites include the urinary bladder, lung, and liver.
An
association has been reported between enterobiasis and lower urinary
tract infections, with the nematode acting as a carrier of enteric
bacteria when it migrates from the perianal region to the urinary
bladder.
Diagnosis is made by identification of
the ova by a cellophane-tape test.
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