Helminths
Intestinal Nematodes: Enterobius vermicularis (Pinworm):Is the most common intestinal parasitic infection worldwide.
Pinworms are particularly common in children.
Geographical Distribution:Pinworm is a cosmopolitan parasite with particularly high prevalence in
countries with a temperate climate.
Habitat:
Adult worm (female resides in cecum and appendix of man).
Morphology:
Adult Worm:
 The male adult worm is 5 mm × 0.5 mm in diameter while
female measures 8 to 12 mm × 0.3 to 0.5 mm.
 The anterior end tapers and is flanked on each side by
cuticular extensions called “cephalic alae”.
 The esophagus is slender, terminating in a prominent
posterior bulb, which is called esophageal bulb. The cephalic
alae and esophageal bulb are important in identification of the
species.
 The posterior end of female is sharp and pointed while it is
curved in males.
11

Male dies after fertilization, while gravid female dies after
oviposition within 2 to 3 weeks.
Figure6: Adult Enterobius vermicularis (Female).
Figure7: Adult Enterobius vermicularis (male).
11
Figure 8: Anterior part of Enterobius vermicularis.
Egg
 Pinworm eggs are colorless, flattened asymmetrically on one
side, ovoid, approximately 55 mm x 25 mm in size, surrounded
by transparent shell and contains coiled tadpole-like larvae,
and embryonate in six hours.
 These eggs can remain viable for about twenty days in a moist
environment.
Figure 9: Enterobius vermicularis egg.
11
Figure 10: Enterobius vermicularis eggs determined by Scotch-tape
Technique.
Life Cycle: The female worm when fully gravid passes down to migrate
several inches outside the anus to deposit eggs.
 These eggs are transferred by fingers (autoinfection) and by
contaminated food or fomites to the mouth and they are
swallowed.
 On reaching the intestine, outer shell is dissolved by digestive
enzyme thus liberating the larvae.
 In the presence of oxygen, larvae become infective worm.
11
Figure 11: Life cycle of Enterobius vermicularis.
Pathogenicity and Clinical Picture:Pinworm infection is usually benign, and are asymptomatic.
The movement of adult worm (female) at the time of laying eggs
causes intense itching and the itching is usually the most severe at
night. inducing the patient to scratch the affected area (anal canal
11
and perianal skin). Scratching may lead to anal lesion and perineal
pruritus, which may be lead to secondary bacterial infections.
Complications are generally associated with extra intestinal infections
in pretoneum, kidney, liver and lungs. Heavy infections cause
insomnia, nightmares, weight loss, convulsion, mucosal ulceration,
submucosal abscesses, mild eosinophilic and lymphocytic infiltration
and granuloma.
Laboratory Diagnosis: The most common means of diagnosing pinworm infection is
via the “Scotch tape” test, where a clear adhesive cellulose
tape is applied to the anal area early in the morning before
bathing or defecation. This is then observed under a
microscope for the presence of pinworm eggs. (a minimum of
four to six consecutive negative tapes is required to rule out
the infection).
 Detection of adult worm in the stools.
 Demonstration of eggs in stool and finger nails, perianal skin
scraping and washings from underwear.
Treatment
 Piperazine, albendazole, and mebendazole are effective.
11