Coccidioides immitis

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The page below is a sample from the LabCE course Mycology: Yeasts and Dimorphic Pathogens. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Coccidioides immitis

The colonies seen growing on the blood agar in the upper image on the right are gray-white and have a delicate hair like consistency. The dark pigmentation indicates that some of the hemoglobin may have been absorbed from the culture medium. The lactophenol blue mount (lower image) reveals thin hyphae that are breaking up into arthroconidia separated by empty cells, giving an alternately staining appearance. This is characteristic of the mold form of Coccidioides immitis.
Coccidioidomycosis is primarily a pulmonary disease. The very light arthroconidia become easily airborne during dust storms in endemic areas in the desert Southwestern United States. Although most cases are contracted from inhalation of wind-blown spores in dust, the considerably higher incidence of human infections near the burrows of desert rodents, including rats, indicates that these infected animals may be involved in concentrating infective spores in the areas where they prowl, particularly from endospores in spherules that are released from decaying carcasses.
Specimens sent to the laboratory may include sputum, gastric washings, cerebrospinal fluid, and pus or biopsy material from skin lesions.
NOTE: The delicate nature, small size and ease of aerosolization of the arthroconidia of Coccidioides immitis could present a considerable danger for laboratory acquired infections, if the appropriate engineering controls and personal protective equipment are not used. Because the arthroconidia are so small and light, they more easily reach the alveolar spaces when inhaled than the conidia of other fungal species. Particularly dangerous are older, mature cultures where spores are highly concentrated and extremely fragile.