[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 8 The Nematodes
201
embryonated eggs are the infective stage for a
new host and, when consumed by a human host,
initiate a new cycle.
Epidemiology
Ascariasis is considered as the most common
intestinal helminth infection in the world, affecting
approximately 1 billion people. It ranks
second in frequency in the United States, the first
being pinworm infection. The regions of the
world and of the United States most susceptible
to harbor Ascaris resemble those for Trichuris—
warm climates and areas of poor sanitation, particularly
where human feces is used as a fertilizer
and where children defecate directly on the
ground. The frequency of A. lumbricoides in the
United States is highest in the Appalachian
Mountains and in the surrounding areas east,
west, and south of them.
The population most at risk of contracting A.
lumbricoides infection is children who place their
contaminated hands into their mouths. Sources
of contamination range from children’s toys to
the soil itself. Persons of all ages may become
infected where vegetables are grown using contaminated
human feces as fertilizer. Although
water has been known to be the source of A.
lumbricoides infection, this occurs only rarely.
As mentioned in Chapter 4, it is suspected that
A. lumbricoides, in addition to pinworm, may be
responsible for the transmission of Dientamoeba
fragilis. This theory has not yet been proven.
Clinical Symptoms
Asymptomatic. Patients infected with a small
number of worms (5 to 10) will often remain
asymptomatic. These patients usually ingest only
a few eggs. They may only learn of their infection
if they happen to notice an adult worm in their
freshly passed feces or if they submit a stool for
a routine parasite examination.
Ascariasis: Roundworm Infection. Patients who
develop symptomatic ascariasis may be infected
with only a single worm. Such a worm may
produce tissue damage as it migrates through the
host. A secondary bacterial infection may also
occur following worm perforation out of the
intestine.
Patients infected with many worms may
exhibit vague abdominal pain, vomiting, fever,
and distention. Mature worms may entangle
themselves into a mass that may ultimately
obstruct the intestine, appendix, liver, or bile
duct. Such intestinal complications may result in
death. In addition, discomfort from adult worms
exiting the body through the anus, mouth, or
nose may occur. Heavily infected children who
do not practice good eating habits may develop
protein malnutrition.
In addition to symptoms relating to the intestinal
phase of ascariasis, patients may also experience
pulmonary symptoms when the worms
migrate through the lungs. During this phase,
patients may develop a low-grade fever, cough,
eosinophilia, and/or pneumonia. An asthmatic
reaction to the presence of the worms, which is
allergic in nature, may also occur.
Treatment
The recommended medications for A. lumbricoides
infections requiring treatment consist of
medications designed to rid the body of parasitic
worms. These include albendazole and
mebenazole.
Prevention and Control
The avoidance of using human feces as fertilizer,
as well as exercising proper sanitation and personal
hygiene practices, are critical measures for
breaking the life cycle of A. lumbricoides.
Quick Quiz! 8-10
Individuals contract Ascaris lumbricoides via which of
the following? (Objective 8-6)
A. Inhalation
B. Insect bite
C. Ingestion
D. Inappropriate sexual practices