[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 8 The Nematodes
male adult characteristically possesses a thin
anterior end equipped with a small mouth, long
and slender digestive tract, and curved posterior
end with two somewhat rounded appendages.
The female differs from the male in two respects.
The female possesses a blunt, rounded posterior
end and a single ovary with a vulva located in
the anterior fifth of the body.
Laboratory Diagnosis
Although clinical symptoms and patient history
play a vital role in helping diagnose T. spiralis
infections, laboratory testing is essential to
confirm all suspicions. Examination of the
affected skeletal muscle is the method of choice
for recovery of the encysted larvae. Serologic
methods are also available. Other laboratory
findings such as eosinophilia and leukocytosis
may also serve as indicators for disease. Elevated
serum muscle enzyme levels, such as lactate dehydrogenase,
aldolase, and creatinine phosphokinase,
may also aid in T. spiralis diagnosis. It is
important to note that several tests may be
required to confirm the presence of T. spiralis.
No known test is completely 100% accurate.
This, coupled with the fact that some tests may
yield false-negative results in early infections,
depending on when the sample is collected, often
accounts for the need to perform multiple tests.
Life Cycle Notes
Human infection with T. spiralis is the result of
accidental human infection with a parasite whose
normal host is an animal (zoonosis). Infection is
initiated after consuming undercooked contaminated
meat, primarily striated muscle. Human
digestion of the meat releases T. spiralis larvae
into the intestine. Maturation into adult worms
occurs rapidly. Mating occurs and the gravid
adult female migrates to the intestinal submucosa
to lay her live larvae because there is no egg stage
in this life cycle. The infant larvae then enter the
bloodstream and travel to striated muscle, where
they encyst nurse cells. Over time, a granuloma
forms, which becomes calcified around these
cells. Because humans are not the traditional
hosts, completion of the T. spiralis life cycle does
not occur and the cycle ceases with the encystation
of the larvae.
Epidemiology
With the exception of the tropics, where it is only
rarely reported, T. spiralis is found worldwide,
particularly in members of the meat-eating population.
This organism may be found in a number
of different animals, including the pig, deer, bear,
walrus, and rat. The wide variety of temperature
zones in which these animals reside suggests that
T. spiralis is resistant to colder regions of the
world as compared with most parasites studied
thus far.
In developed areas, it is presumed that the
feeding of contaminated pork scraps to hogs
accounts for a major mode of T. spiralis transmission.
Similarly, other animals contract this
parasite from consuming contaminated meat.
Clinical Symptoms
Trichinosis, Trichinellosis. T. spiralis is known
as the great imitator because infected patients
may experience a variety of symptoms that often
mimic those of other diseases and conditions.
Persons with a light infection typically experience
diarrhea and possibly a slight fever, suggestive
of the flu. Heavily infected patients complain
of symptoms such as vomiting, nausea, abdominal
pain, diarrhea, headache, and perhaps a fever
during the intestinal phase of infection. As the
larvae begin their migration through the body,
infected persons experience a number of symptoms,
particularly eosinophilia, pain in the
pleural area, fever, blurred vision, edema, and
cough. Death may also result during this phase.
Muscular discomfort, edema, local inflammation,
overall fatigue, and weakness usually
develop once the larvae settle into the striated
muscle and begin the encystation process. The
striated muscle of the face and limbs, as well as
that of other parts of the body, may become
infected.