[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 10 The Cestodes
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have particularly been useful in situations in
which the hydatid cyst was inoperable.
Prevention and Control
To break the E. granulosus life cycle and subsequently
halt the spread of human disease, the
implementation of several measures is essential.
These include implementing appropriate personal
hygiene practices to prevent ingestion of the eggs,
discontinuing the practice of feeding canines
potentially contaminated viscera, promptly treating
canines and humans who become infected,
and instituting a thorough education program for
those in high-risk areas for transmission of the
parasite.
Notes of Interest and New Trends
Echinococcus multilocularis is an accidental
cause of hydatid disease in humans living in the
Subarctic, as well as central Europe and India.
Foxes are the primary definitive hosts; rodents,
such as mice and voles, are the usual intermediate
hosts. Disease manifestion in humans is similar
to that of E. granulosus.
Quick Quiz! 10-19
Which of the following procedures would not be
appropriate for diagnosing an infection with Echinococcus
granulosus? (Objective 10-8)
A. Serologic procedure, such as ELISA
B. O&P examination of stool specimen
C. CT scan of suspect organ
D. Biopsy of cyst
Quick Quiz! 10-20
In humans, Echinococcus granulosus infection results
in which of the following? (Objective 10-5)
A. Eggs similar to those of H. nana
B. A nutritional deficiency
C. A hydatid cyst
D. Filariform larva
Quick Quiz! 10-21
Which of the following is not a usual site for Echinococcus
granulosus infection in humans? (Objective
10-8)
A. Brain
B. Liver
C. Lung
D. Genitalia
LOOKING BACK
Careful examination of the cestode eggs, scolices,
and proglottids is essential for speciation of the
organism. Comparison drawings, such as those
provided at the end of this chapter, can be a
useful resource and may aid in the determination
of the cestodes.
With the exception of D. latum, all the remaining
intestinal tapeworm eggs consist of a hexacanth
embryo with six hooklets. The presence of
structures such as radial striations, polar thickenings,
and filaments are helpful in species identification.
The presence of egg packets suggests the
presence of D. caninum. D. latum is unique in
that it consists of a coracidium, operculum, and
terminal knob.
Similarly, with the exception of D. latum, all
the remaining intestinal tapeworm scolices have
four cuplike suckers. The presence of a rostellum
and row(s) of hooks aid in identifying the species.
Two long almond-shaped suckers comprise the
scolex of D. latum, making this organism easy
to distinguish from the others.
The proglottids of the intestinal tapeworms,
particularly those that are gravid, vary in several
respects. These include shape, number of uterine
branches, if present, and location of the uterine
structure, where appropriate.
The E. granulosus hydatid cyst, the only intestinal
tissue tapeworm species, may be identified
by the presence of all or some of the following:
a fluid-filled bladder surrounded by a cyst wall
and multiple layers of laminated germinal tissue
from which daughter cysts and/or brood capsules
may develop. Older cysts may evolve into and be
seen as hydatid sands.