Biomedical Engineering Reference
In-Depth Information
colonization of the airways, without disease. Alternately, they may provoke
an acute or chronic allergic reaction in the lungs. The organism can grow in
respiratory mucosa, or it may invade into the lung tissue. It may produce
large fungal masses, or it may invade diffusely through the lung, like a pneu-
monia. Or it may produce a fungemia, and disseminate throughout the body.
Spores of Aspergillus species are found in the air, and everyone is exposed
to these fungi. Disease most often occurs in immune-compromised indivi-
duals. Primary cutaneous aspergillosis is a rare form of aspergillosis that
occurs in the skin of immune-compromised patients near the site of indwelling
intravenous lines.
Genus Penicillium contains one species that is known to produce human
disease: Penicillium marneffei. Infections occur primarily in Southeast Asia,
and most reported cases have occurred in AIDS patients. The disease, known
as penicillosis, can produce systemic disease. This species, like many of the
other highly pathogenic members of Class Ascomycota,
is a dimorphic
fungus.
Chromoblastomycosis can be caused by a variety of organisms that belong
to Class Herpotrichiellaceae: Fonsecaea pedrosoi, Phialophora verrucosa,
Cladophialophora carrionii, and Fonsecaea compacta. Chromoblastomycosis
begins as a skin papule, at the site of entry, and over the years may slowly
spread.
Cladophialophora bantiana can produce phaeohyphomycotic brain
abscesses and subcutaneous lesions in both normal and immunosuppressed
patients.
Class Onygenales contains many of the fungi that characteristically cause
disease in immune-competent individuals, and it is the only class of fungi
containing organisms that infect, disseminate, and sometimes kill otherwise
healthy persons, with one important qualification. Good health is hard to
establish with certainty, and the biological relationships between human host
and fungal infection can be very complex. Although most pathogenic fungi
produce clinical disease in immune-deficient individuals, you will occasion-
ally encounter a supposedly normal person who develops a fulminant infec-
tion from a supposedly non-pathogenic or opportunistic fungus. Nonetheless,
there are a few fungi that produce disease in healthy patients, and most of
these belong to Class Onygenales. Paracoccidioides brasiliensis (paracocci-
dioidomycosis or South American blastomycosis), along with Coccidioides
immitis (coccidioidomycosis or valley fever), Blastomyces dermatitidis
(blastomycosis), and Histoplasma capsulatum (histoplasmosis), are highly
pathogenic. Each is characterized by the growth of yeast (round cells) in
diseased tissues, and each is dimorphic in culture medium. All four are sys-
temic mycoses that begin as lung infections. All four grow in the soil or, in
the case of Histoplasma capsulatum, in bat or bird guano. Each has its own
geographic distribution. Paracoccidioidomycosis is found in South America;
coccidioidomycosis in the Southwestern USA, blastomycosis in the Midwest
