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Ascaris
lumbricoides is a nematode of worldwide distribution, most prevalent
in tropical and subtropical countries. The incidence and
severity of the infection are closely related to hygienic levels.
The adult
worms range from 15 to 30 cm in length and from 3 to 5 mm in diameter.
Clinical
presentation:
The patients may
often present with a history of passing worms by mouth or anus.
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A number of
patients, presents with a subacute clinical course ; some patients have
acute presentation, with severe abdominal pain, fever, dehydratation,
vomiting, and abdominal distension and may require vigorous fluid
resuscitation and emergency surgical intervention.
In some cases
the adult parasite can invade the biliary or pancreatic ducts and
cause obstruction with development of jaundice, cholecystitis,
ascending cholangitis,
pancreatitis, and hepatic abscesses.
A clinical
picture resembling bronchial asthma and diffuse peribronchitis, with
occasional hemoptysis, is sometimes noted.
Physicians
should have a high index of suspicion for parasitic infestation in
warm climates where economically deprived children present with
symptoms of intestinal obstruction.
Life
Cycle:
The eggs are
deposited in the soil, where they undergo a period of incubation.
The infection
is acquired by ingestion of the fully embryonated ova.
The larvae are
hatched in the small intestine and penetrate the wall, reaching the
lungs by way of venules or lymphatics.
They pass into
the alveoli from the alveolar capillaries and migrate up the main
bronchial tree and down the esophagus with swallowed saliva.
In the small
intestine they grow into adult males or females.
Pathological
features:
In severe
infections, during the period of lung migration, the larvae produce
areas of hemorrhage and inflammatory reaction characterized by the
presence of neutrophils and eosinophils.
Ascariasis is
usually a benign and self-limited disease because of the short life
span of the adult worm (6 to 12 months).
The most
frequent complications of ascariasis are caused by the adult parasite.
Large masses
of worms may produce intestinal obstruction and rarely may lead to
perforation and peritonitis.
Although
ascariasis has been shown to have an adverse effect on nutritional
status, there is little evidence that it can cause intestinal
malabsorption.
Ascaris worms
have a tendency to wander into natural passages and may migrate into
the biliary system, pancreatic duct or lumen of the appendix.
Occasionally the adult worms migrate into the upper respiratory
passages.
Diagnosis:
Diagnosis is based on faecal examination.
Serological
tests have been developed but are rarely used for diagnostic purposes.
Abdominal
roentgenograms, usually show a "whirlpool" pattern of intraluminal
worms.
Ultrasonography can detect worms in the biliary tract and pancreas and
is a useful noninvasive technique for diagnosis and follow-up of such
patients. ERCP can help diagnose biliary and pancreatic
ascariasis, including ascaris in the duodenum. Also, ERCP can be used
to extract worms from the biliary and pancreatic ducts when indicated.
Ascaris Suis:
(pig roundworm):
Closely related to A. lumbricoides and can sometimes infect humans. In
humans A. suis develops to the larval tissue - migratory stages and
rarely reaches the adult intestinal stage. The true incidence of A.
suis infection in humans is unknown.
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