Page 431 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com PNEUMOCYSTIS mebooksfree.com mebooksfree.com
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420
PART V Mycology
Pneumocystis jiroveci is classified as a yeast on the basis of
molecular analysis, but it has many characteristics of a pro-
tozoan. Some regard it as an “unclassified” organism. A
summary of the important clinical information is presented
here and a more detailed description is presented in
Chapter 52 with the blood and tissue protozoa. In 2002,
taxonomists renamed the human species of Pneumocystis
as P. jiroveci and recommended that P. carinii be used only
mebooksfree.com mebooksfree.com mebooksfree.com organisms into the lungs. An inflammatory exudate com- mebooksfree.com
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to describe the rat species of Pneumocystis.
Pneumocystis is acquired by inhalation of airborne
posed primarily of plasma cells occurs, oxygen exchange is
reduced, and dyspnea occurs. A reduced number of CD
4-postive T lymphocytes, such as occurs in AIDS, predis-
FIGURE 50–13
Mucor species—mucormycosis. Note necrotic
poses to pneumonia. Most immunocompetent people have
area involving the nose and face. (Reproduced with permission from
asymptomatic infections.
Lichtman MA et al, eds. Lichtman’s Atlas of Hematology. New York:
The clinical findings of Pneumocystis pneumonia
McGraw-Hill, 2007. Copyright © 2007 by The McGraw-Hill
include fever, nonproductive cough, and dyspnea. Rales are
Companies, Inc.)
heard bilaterally and the chest X-ray shows a “ground-
glass” pattern. The mortality rate of untreated Pneumocystis
pneumonia is approximately 100%.
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difficult to culture because they are a single, very long cell,
The diagnosis is typically made by finding the cysts of
and damage to any part of the cell can limit its ability to
Pneumocystis in bronchial lavage specimens. Fluorescent
grow.
antibody stains or tissue stains, such as methenamine silver
If diagnosis is made early, treatment of the underlying
disorder, plus administration of amphotericin B and surgi-
tests are also used. Serological tests are not useful.
cal removal of necrotic infected tissue, has resulted in some
The drug of choice for Pneumocystis pneumonia is trim-
remissions and cures. Liposomal amphotericin B should be
ethoprim-sulfamethoxazole. Trimethoprim-sulfamethoxa-
used in patients with preexisting kidney damage. Posacon-
zole or aerosolized pentamidine can be used for prophylaxis
azole can also be used.
in patients with CD4 counts below 200.
FUNGI OF MINOR IMPORTANCE tissue closely resemble those of Aspergillus. In culture, the
mebooksfree.com mebooksfree.com mebooksfree.com mycelium (brownish-gray) of P. boydii are different from mebooksfree.com
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PENICILLIUM MARNEFFEI
appearance of the conidia (pear-shaped) and the color of the
Penicillium marneffei is a dimorphic fungus that causes
tuberculosis-like disease in AIDS patients, particularly in
those of Aspergillus. The drug of choice is either ketocon-
Southeast Asian countries such as Thailand. It grows as a mold
azole or itraconazole because the response to amphotericin B
that produces a rose-colored pigment at 25°C but at 37°C
is poor. Debridement of necrotic tissue is important as well.
grows as a small yeast that resembles Histoplasma capsulatum.
Bamboo rats are the only other known hosts. The diagnosis is
made either by growing the organism in culture or by using
fluorescent antibody staining of affected tissue. The treatment
Fusarium solani is a mold that causes disease primarily in
of choice consists of amphotericin B for 2 weeks followed by
neutropenic patients. Fever and skin lesions are the most com-
oral itraconazole for 10 weeks. Relapses can be prevented with FUSARIUM SOLANI
mon clinical features. The organism is similar to Aspergillus in
prolonged administration of oral itraconazole.
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that it is a mold with septate hyphae that tends to invade blood
vessels. Blood cultures are often positive in disseminated dis-
PSEUDALLESCHERIA BOYDII
amphotericin B is the drug of choice. Indwelling catheters
Pseudallescheria boydii is a mold that causes disease primar-
should be removed or replaced. In 2006, an outbreak of
ily in immunocompromised patients. The clinical findings
Fusarium keratitis (infection of the cornea) occurred in people
who used a certain contact lens solution.
and the microscopic appearance of the septate hyphae in
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