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Intestinal Nematodes 137

infection. Personal hygiene and sanitary living condi- ■ Eggs may be seen with the naked eye, clinging to the
tions are necessary to avoid becoming infected and then skin around the anus
reinfected. Although pinworm infections are relatively ■ Pinworms do not contribute to abdominal pain but
harmless, they are a nuisance but are easily treated, and have, perhaps erroneously, been attributed to cases
ridding the entire family of the annoying symptoms of of appendicitis as they have been observed in tissue
the disease is required to effectively control the infection. specimens such as the appendix.

ENTEROBIUS VERMICULARIS Life Cycle

Enterobius vermicularis is called a pinworm due to its Most infections originate from soiled fingers coming in
long pointed tail that resembles a straight pin in the adult contact with the mouth or when pinworm eggs are eaten,
worm. These pinworms may be visible in the stools of but they may occur through contaminated food, bedding,
those infected, and are readily visible in the feces of chil- clothing, or other personal items. The pale-colored adult
dren with heavy infections, but the diagnosis is generally pinworm, of slightly less than one-half inch in size, is easy
made by the presence of eggs. to visualize in the feces during heavy infections. Since the
female dies upon laying her eggs, reinfection must occur
cyclically in order to maintain an ongoing infection.
Morphology
Approximately 1 month following infestation of the
As a common trait in nematodes, the female worm is gut, the adult female will move down the intestinal system
larger than the male and may reach a length of 7 to 13 mm, and will exit the body through the anus. There she lays
making the adult females easily visible in the stools from a batch of several hundred eggs on the skin surrounding
an infected individual. The adult males may be largely the anus, usually during the night or early in the morn-
unnoticed because they are so small. The egg of the spe- ing before light enters the bedroom. Severe itching often
cies is oval but flattened on one side. It has a thick and accompanies the laying of the eggs, especially at night. In
colorless shell and measures 50 to 60 μm in length by 20 this way children are able to reinfect themselves by soiling
to 30 μm in width. Larvae may be visible inside the egg their fingers and also accumulating eggs on the fingers and
due to the colorless shell of the embryonated eggs. under the nails from the bed linens. The cycle of repro-
duction by transfer of the eggs to the mouth where they
are again swallowed ensures a steady source of infection.
Symptoms
Also, the eggs may remain viable for up to several days if
Symptoms often range from being ssymptomatic to any the conditions are suitable.
or several of the following signs and symptoms. An itchy
anus due to an inflammatory response to the adult worm, Disease Transmission
especially at night, will be the most frequent symptom
exhibited. In addition to this manifestation, any or all of The infection is spread via the fecal-oral route by
the following may be present: ingestion or inhalation of embryonated ova. The disease
may also be transmitted by fomites (inanimate objects that
■ Irritability may occur in children along with are contaminated by organisms) and from soiled fingers,
nervousness and disruptive behavior
dirty bed linens, toilet seats, and clothing. The disease is
■ With severe scratching of the anus, the skin may break found throughout the world and spreads quickly through
down and progress to a secondary bacterial infection families and groups in close contact with each other, such
■ Rare cases appear to cause anorexia, or loss of appetite as in day care centers for young children.
■ Somewhat vague or ill-defined feelings of not being
well may be present Laboratory Diagnosis
■ Female children may also have an itchy and
The “Scotch tape test” is the most economical, easi-
inflamed vagina est, and effective means of diagnosing infection with
■ Adult worms may be seen in the stools E. vermicularis. Applying a piece of transparent