Biomedical Engineering Reference
In-Depth Information
tract, or the skin. Once on a mucosal surface, an acute allergic response
may occur (e.g. sneezing). After a time, the colony fails to thrive due to
an inhospitable environment (e.g. insufficient food, poor ionic milieu,
effective host immune response).
5.
After exposure, fungi permanently colonize the mucosal surface, with no
clinical effect. Candida species commonly colonize the mouth and the
vagina. Aspergillus species may colonize the respiratory surfaces (e.g.
bronchi). In many cases, we simply carry fungal colonies as commensals
(organisms that live within us, without causing disease).
6.
Colonies persist, but the host reacts with an acute or chronic immune
response. Chronic allergic aspergillosis of the bronchi is a good example.
The patient may have a chronic cough. Microscopic examination of bron-
chial mucosa may reveal some inflammation, the presence of eosinophils,
and the occasional hypha. Sometimes the host response is granulomatous,
producing small nodules lining the bronchi, containing histiocytes and
lymphocytes. A truce between the fungal colony and the host response is
sometimes attained, in which the fungus colonies never leave, the inflam-
mation never regresses, but the fungus does not invade into the underlying
mucosa.
7.
Fungi invade through the mucosa into the submucosa and underlying tis-
sue. These locally invasive infections often manifest as a fungal ball,
consisting of varying amounts of inflammatory tissue, necrosis, and fun-
gal elements.
8.
Fungal elements invade into lymphatics, traveling with the lymph fluid,
and producing regional invasive fungal disease along the route of lym-
phatic drainage. The prototypical example of this process is found in
infections with Sporothrix schenckii, which typically gains entrance to
the skin, from the soil, through abrasions. Infection yields multiple skin
papules, emanating from the point of primary infection (usually the
hand or the foot), and following line of lymphatic drainage.
9.
Fungal elements invade into blood vessels.
10.
Fungal elements become a blood constituent (i.e. fungemia) and dissem-
inate throughout the body.
11.
Fungal elements spread throughout the body to produce invasive fungal
infections in multiple organs.
The most perplexing aspect of fungal infections is that a single fungus may
manifest itself by any and all of these biologic options (e.g. Aspergillus and
and Malassezia species, see below). In general, the more immune-competent
the individual, the less likely that a fungal infection will become clinically
significant or life-threatening.
Readers should be aware that pathologists have developed a wide variety
of techniques to identify fungi based on their morphologic features in tissue
biopsies (e.g. the presence or absence of pigment, the presence or absence of
