Page 469 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART VI Parasitology
The treatment of choice is praziquantel.

Prevention
Prevention involves cooking beef adequately and disposing
waste properly so that cattle cannot consume human feces.

mebooksfree.com mebooksfree.com mebooksfree.com DIPHYLLOBOTHRIUM mebooksfree.com mebooksfree.com
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Disease

Diphyllobothrium latum, the fish tapeworm, causes
diphyllobothriasis.
FIGURE 54–6
Cysticercus of Taenia solium in brain—long
arrow points to a larva of T. solium. Short arrow points to the wall of
Important Properties
the cysticercus (sac) that surrounds the larva. (Used with permission from
Rhodes B. Holliman, PhD, Professor Emeritus, Virgina Tech.)
In contrast to the other cestodes, which have suckers,
the scolex of D. latum has two elongated sucking
The disease occurs worldwide but is endemic in Africa,
grooves by which the worm attaches to the intestinal wall
South America, and Eastern Europe. In the United States,
(see Figure 54–2E). The scolex has no hooks, unlike
most cases are imported.
T. solium and Echinococcus. The proglottids are wider than
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Clinical Findings
rosette. Unlike other tapeworm eggs, which are round,
D. latum eggs are oval and have a lidlike opening (operculum)
Most patients with adult tapeworms are asymptomatic, but
at one end (see Figure 54–4B). Diphyllobothrium latum is
malaise and mild cramps can occur. In some, proglottids
the longest of the tapeworms, measuring up to 13 m.
appear in the stools and may even protrude from the anus.
Humans are infected by ingesting raw or undercooked
The proglottids are motile and may cause pruritus ani as
fish containing larvae (called plerocercoid or sparganum
they move on the skin adjacent to the anus.
larvae). In the small intestine, the larvae attach to the gut
wall and develop into adult worms. Gravid proglottids
Laboratory Diagnosis
release fertilized eggs through a genital pore, and the eggs
Identification of T. saginata consists of finding gravid pro-
are then passed in the stools. The immature eggs must be
glottids with 15 to 20 uterine branches in the stools. Eggs
deposited in fresh water for the life cycle to continue. The
are found in the stools less often than are the proglottids.
embryos emerge from the eggs and are eaten by tiny cope-
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differentiate and form procercoid larvae in the body cavity.
When the copepod is eaten by freshwater fish (e.g., pike,
trout, and perch), the larvae differentiate into plerocercoids
in the muscle of the fish (second intermediate host). The
cycle is completed when raw or undercooked fish is eaten
by humans (definitive hosts).
Pathogenesis & Epidemiology
Infection by D. latum causes little damage in the small
intestine. In some individuals, megaloblastic anemia occurs
as a result of vitamin B deficiency caused by preferential
12
uptake of the vitamin by the worm.
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The epidemiology of D. latum infection is related to the
ingestion of raw or inadequately cooked fish and to con-
tamination of bodies of fresh water with human feces. The
FIGURE 54–7
Taenia saginata—adult tapeworm. Note the tiny
scolex on the right side of the image and the gravid proglottids on
eating raw fish is the custom, such as Scandinavia, northern
the left side of the image. White arrow points to the scolex. Ruler is
Russia, Japan, Canada, and certain north-central states of
12 inches long. (Source: Public Health Image Library, Centers for
the United States.
Disease Control and Prevention.)

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