Page 419 - Review of Medical Microbiology and Immunology ( PDFDrive )

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408
PART V Mycology

Arthrospores

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mebooksfree.com mebooksfree.com mebooksfree.com of the wall, endospores are released and differentiate to mebooksfree.com

Spherule with
endospores
A
B
FIGURE 49–1
Stages of Coccidioides immitis. A: Arthrospores form at the ends of hyphae in the soil. They germinate in the soil to
form new hyphae. If inhaled, the arthrospores differentiate into spherules. B: Endospores form within spherules in tissue. When spherules
rupture, endospores disseminate and form new spherules. (Reproduced with permission from Brooks GF et al. Medical Microbiology. 20th ed. Originally pub-
lished by Appleton & Lange. Copyright 1995 McGraw-Hill.)

Transmission & Epidemiology

The fungus is endemic in arid regions of the southwestern
mebooksfree.com mebooksfree.com mebooksfree.com form new spherules. The organism can spread within a mebooksfree.com
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person by direct extension or via the bloodstream. Granu-
United States and Latin America. People who live in Cen-
lomatous lesions can occur in virtually any organ but are
tral and Southern California, Arizona, New Mexico, Western
found primarily in bones and the central nervous system
Texas, and Northern Mexico, a geographic region called the
(meningitis).
Lower Sonoran Life Zone, are often infected. In soil, it forms
Dissemination from the lungs to other organs occurs in
hyphae with alternating arthrospores and empty cells
people who have a defect in cell-mediated immunity. Most
(Figure 49–2). Arthrospores are very light and are carried by
people who are infected by C. immitis develop a cell-
the wind. They can be inhaled and infect the lungs.
mediated (delayed hypersensitivity) immune response that
restricts the growth of the organism. One way to determine
Pathogenesis
In the lungs, arthrospores form spherules that are large
immunity to the organism is to do a skin test (see later). In
(30 mm in diameter), have a thick, doubly refractive wall,
general, a person who has a positive skin test reaction has
and are filled with endospores (Figure 49–3). Upon rupture whether a person has produced adequate cell-mediated
developed sufficient immunity to prevent disseminated
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mebooksfree.com mebooksfree.com mebooksfree.com FIGURE 49–3 Coccidioides immitis—spherule. Long arrow mebooksfree.com
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FIGURE 49–2
Coccidioides immitis—arthrospores. Barrel-
shaped, rectangular arthrospores appear blue with lactophenol
points to a spherule in lung tissue. Spherules are large thick-walled
structures containing many endospores. Short arrow points to an
-cotton blue stain. Arthrospores are also called arthroconidia.
endospore. (Source: Dr. L. Georg, Public Health Image Library, Centers for Disease
(Source: Dr. Hardin, Public Health Image Library, Centers for Disease Control and
Prevention.)
Control and Prevention.)

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