Page 491 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART VI Parasitology
480
Trichinosis
Larva deposited
(Trichinella spiralis)
in mucosa

Adults in

Larva released
in small intestine small intestine Human Circulation
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mebooksfree.com mebooksfree.com in small intestine small intestine mebooksfree.com nurse cell in human mebooksfree.com

Adults in
Encysted larva in
striated muscle
Larva released
Larva deposited
in mucosa
Pigs and
other carnivores, e.g., bears Circulation
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mebooksfree.com mebooksfree.com Encysted larva in (diagnostic stage) mebooksfree.com mebooksfree.com
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Ingested
Encysted larva in
striated muscle

striated muscle
(infective stage)

Meat
(Pork, etc.)
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FIGURE 56–14
Trichinella spiralis. Life cycle. Top: Blue arrow on left shows ingestion of meat (muscle) containing encysted Trichinella
larva. Adult worms form in intestine and produce larvae that enter bloodstream and encyst in human muscle. Bottom: Red circular arrow
describes the natural cycle in which Trichinella circulates between pigs and various carnivores such as bears. (Source: Public Health Image Library, Cen-
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mebooksfree.com mebooksfree.com mebooksfree.com reservoir hosts, primarily swine and rats. Humans are end- mebooksfree.com
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ters for Disease Control and Prevention.)
The parasite is maintained in nature by cycles within
to many organs; however, they develop only in striated
muscle cells. Within these “nurse cells,” they encyst within
stage hosts, because the infected flesh is not consumed by
a fibrous capsule and can remain viable for several years but
other animals.
eventually calcify (Figure 56–15).

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