ANSWERS TO QUESTIONS:
This particular
helminth belongs to the nematode (roundworm) group. It can be identified
as an Ascaris lumbricoides adult worm; based on the curved tail,
it is an adult male worm. Since this is considered a pathogen, the patient
should be treated. Although the patient passed an adult worm, It is
important to realize that other worms may be present in the intestine.
COMMENTS
ON THE PATIENT:
Other
laboratory findings were all within normal range. After therapy, the
patient passed several more adult worms, and both fertilized and unfertilized
eggs were seen in the concentration sediment wet preparations.
(Left):
fertilized egg; (Right): unfertilized egg (note the very bumpy shell on
the more elongated unfertilized egg)
COMMENTS
ON
DIAGNOSTIC METHODS:
During
the O & P examination, both fertilized and unfertilized eggs were recovered
from the stool sedimentation concentration procedure. Due to the large number
of eggs produced each day by the female worm, the presence of eggs can almost
always be detected with a single stool examination. The presence of unfertilized
eggs only would indicate the presence of female worm(s) only.
Remember
that the unfertilized Ascaris eggs will not float with the use of
the zinc sulfate flotation concentration method (the eggs are too heavy).
Also, if too much iodine is added to the wet mount preparations, the eggs
may look like darkly stained debris. Eggs may be very difficult to identify
on a permanent stained smear because of stain retention and asymmetric shape.
Intestinal
disease can often be diagnosed from radiographic studies of the gastrointestinal
tract.
COMMENTS
ON THE INFECTION:
The number
of people in the world infected with A. lumbricoides is probably
second only to the number infected with the pinworm, Enterobius vermicularis.
Infection
in humans is acquired through ingestion of the embryonated eggs from contaminated
soil. On ingestion, the eggs hatch in the stomach and duodenum, where the
larvae actively penetrate the intestinal wall; they are then carried to
the right heart via the hepatic portal circulation. Then the larvae are
carried into the pulmonary circulation, where they are filtered out by the
capillaries. After approximately 10 days in the lung, the larvae break into
the alveoli, migrate via the bronchi until they reach the trachea and pharynx,
and then are swallowed. The worms then mature and mate in the intestine,
with the eventual production of eggs, which are passed in the stool. The
entire developmental process from egg ingestion to egg passage from the
adult female takes from 8 to 12 weeks. During her life span, she may deposit
a total of 27,000,000 eggs.
Both unfertilized and fertilized eggs are passed. Often only female worms
are recovered from the intestine. However, in this case, a male worm was
passed in the stool. Fertilized eggs will become infective within 2 weeks
if they are in moist, warm soil, where they may remain viable for months
or even years. The fertilized egg is broadly oval, with a thick, mammillated
coat, usually bile stained a golden brown. These eggs measure up to 75 µm
long and 50 µm wide. Unfertilized eggs are usually more oval, measure
up to 90 µm long, and may have a pronounced mammillated coat or an
extremely minimal mammillated layer. Often both types of eggs are found
in the same stool specimen. The total absence of fertilized eggs means that
only female worms are present in the intestine.
Other involved
body sites may present specific symptoms indicative of bowel obstruction,
biliary or pancreatic duct blockage, appendicitis, or peritonitis. The presence
of the adult worms in the intestine usually caused no difficulties unless
the worm burden is very heavy; however, because of the tendency of the adult
worms to migrate, even a single worm can cause serious sequelae. Worm migration
may occur as a result of stimuli such as fever, the use of general anesthesia,
or other abnormal conditions. This migration may result in intestinal blockage;
entry into the bile duct, pancreatic duct, or other small spaces; or entry
into the liver or peritoneal cavity. They can also migrate out of the anus
or come out the mouth or nose.
There can
also be signs of pneumonitis if the number of larvae migrating through the
liver and lungs is quite large. The picture of transient pulmonary infiltrates
that clear within a couple of weeks and are associated with peripheral eosinophilia
is frequently called Loeffler's syndrome. Larvae can be recovered from sputum;
however, this is not a common findings.
The transmission
of ascariasis depends on fecal contamination of the soil and the ingestion
of soil contaminated with infective eggs. There are apparently no practical
means of killing the eggs while they are in the soil. The adult worms will
survive from 1 to 2 years.
REFERENCES
Garcia,
L.S. 2001. Diagnostic Medical Parasitology, 4th Ed., ASM Press,
Washington, D.C.
Garcia,
L.S.1999. Practical Guide to Diagnostic Parasitology, ASM Press, Washington,
D.C.
Isenberg,
H. D. (ed.). 2004. Clinical Microbiology Procedures
Handbook, 2nd Ed, vol. 1, 2 and 3. ASM Press, Washington, D.C.
