Etiologic agents:
Blastomyces dermatitidis, Coccidioides immitis and Histoplasma capsulatum
- All of these agents are "dimorphic fungi,"
meaning that they exist in two different phases:
- yeast phase (reproduce by budding) - This is the form of
the organism that occurs in the tissues of infected animals or
people.
- mycelial phase (reproduce by production of hyphae and conidia)
- This is the form of the organism that occurs in the environment
(soil) AND during culture in vitro.
Cryptococcus neoformans
- A systemic yeast infection; not a dimorphic fungus.
THESE ARE ALL SAPROPHYTIC ORGANISMS THAT DOMESTIC ANIMALS
AND PEOPLE EACH ACQUIRE FROM THE SOIL.
- Animals may, however, serve as important sentinels for the
presence of the organisms in a given geographic region.
ANIMALS DO NOT, UNDER ROUTINE CIRCUMSTANCES, SERVE AS A
DIRECT ZOONOTIC RISK FOR HUMAN INFECTION.
- There may be a limited potential risk to humans of accidental
contamination of open wounds with the yeast form of these organisms
from an infected animal's lesions. For instance, case reports
have described blastomycosis in human beings bitten by a dog
with blastomycosis, via cutaneous contact during a post-mortem
examnation and following accidental intramuscular injection of
Blastomyces organisms from a canine pulmonary aspirate.
Overall, however, the risk of direct zoonotic infection from
infected animals is remote.
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