Page 470 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 54 Cestodes
Clinical Findings
can sensitize the host. Later, if the cyst ruptures spontane-
Most patients are asymptomatic, but abdominal discomfort
ously or during trauma or surgical removal, life-threatening
and diarrhea can occur.
anaphylactic shock can occur. Rupture of a cyst can also
spread protoscoleces widely.
Laboratory Diagnosis
The disease is found primarily in shepherds living in the
Diagnosis depends on finding the typical eggs (i.e., oval,
the United States, the western states report the largest num-
yellow-brown eggs with an operculum at one end, in the
ber of cases.
stools). There is no serologic test. Mediterranean region, the Middle East, and Australia. In
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Clinical Findings
Treatment
Many individuals with hydatid cysts are asymptomatic, but
The treatment of choice is praziquantel.
can erode into a bronchus, causing bloody sputum, and
Prevention
cerebral cysts can cause headache and focal neurologic
Prevention involves adequate cooking of fish and proper
signs. Rupture of the cyst can cause fatal anaphylactic shock.
disposal of human feces.
Laboratory Diagnosis
ECHINOCOCCUS
Diagnosis is based either on microscopic examination
demonstrating the presence of brood capsules containing
Disease
multiple protoscoleces or on serologic tests (e.g., the indi-
Echinococcus granulosus (dog tapeworm) causes echino-
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coccosis. The larva of E. granulosus causes unilocular
Treatment
hydatid cyst disease. Multilocular hydatid disease is caused
by E. multilocularis, which is a minor pathogen and is
Treatment involves albendazole with or without surgical
discussed later.
removal of the cyst. Extreme care must be exercised to pre-
vent release of the protoscoleces during surgery. A proto-
Important Properties
scolicidal agent (e.g., hypertonic saline) should be injected
Echinococcus granulosus is composed of a scolex and only
into the cyst to kill the organisms and prevent accidental
three proglottids, making it one of the smallest tapeworms
dissemination.
(see Figures 54–2F and G). The scolex has a circle of hooks
and four suckers similar to T. solium. Dogs are the most
important definitive hosts. The intermediate hosts are usu-
Prevention of human disease involves not feeding the
ally sheep. Humans are almost always dead-end intermedi- Prevention
entrails of slaughtered sheep to dogs.
ate hosts.
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The life cycle of E. granulosus is shown in Figure 54–8.
In the typical life cycle, worms in the dog’s intestine liberate
CESTODES OF MINOR IMPORTANCE
thousands of eggs, which are ingested by sheep (or humans)
(see Figure 54–4). The oncosphere embryos emerge in the
small intestine and migrate primarily to the liver but also to
Many of the features of this organism are the same as those
the lungs, bones, and brain. The embryos develop into large
of E. granulosus, but the definitive hosts are mainly foxes
fluid-filled hydatid cysts, the inner germinal layer of which
and the intermediate hosts are various rodents. Humans are
generates many protoscoleces within “brood capsules.” The
infected by accidental ingestion of food contaminated with
life cycle is completed when the entrails (e.g., liver contain-
ing hydatid cysts) of slaughtered sheep are eaten by dogs.
pers and is endemic in northern Europe, Siberia, and the
western provinces of Canada. In the United States, it occurs
Pathogenesis & Epidemiology fox feces. The disease occurs primarily in hunters and trap-
in North and South Dakota, Minnesota, and Alaska.
Within the human liver, the larvae form multiloculated
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Echinococcus granulosus usually forms one large fluid-filled
cysts with few protoscoleces. No outer fibrous capsule
cyst (unilocular) that contains thousands of individual
forms, so the cysts continue to proliferate, producing a
scoleces as well as many daughter cysts within the large
cyst. Individual scoleces lying at the bottom of the large
cal picture usually involves jaundice and weight loss. The
cyst are called “hydatid sand”. The cyst acts as a space-
prognosis is poor. Albendazole treatment may be successful
occupying lesion, putting pressure on adjacent tissue. The
in some cases. Surgical removal may be feasible.
outer layer of the cyst is thick, fibrous tissue produced by
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