Coccidioides immitis (Coccidioidomycosis, San Joaquin Valley fever, desert fever, desert rheumatism)

General: Found in the Western hemisphere, particularly the southwestern U.S. and into Central and South America.

Clinical: Outbreaks occur following dust storms, earthquakes, and earth excavation with dispersion of spores (arthroconidia). In the lungs, they transform into spherules, with symptoms (mild to moderate flu-like illness) developing 7~21 days post-exposure. Infection usually resolves spontaneously and rapidly. Rarely, it lingers as a chronic infection or may disseminate to any organ; the disseminated cutaneous form can produce markedly disfiguring keratotic &/or verrucous ulcers and abscesses. Although initial responses are humoral, recovery relies heavily upon T-cell mediated cellular response (<200 CD4 T-cells/µl = more likely to have severe, disseminated infections). There is an unexpected predisposition (~x10) among African-Americans and Filipinos to develop disseminated disease, presumably a genetic susceptibility.

• Normal:
• Abnormal:

Resistance:

Morphology: This dimorphic fungus produces an acute suppurative (around endospores after spherule rupture) and granulomatous response (around developing spherules). Hyphae may be seen in pulmonary cavities and meningeal lesions (which may lack spores altogether, causing confusion with Aspergillus). It produces barrel-shaped arthroconidia 2-4 x 3-6 um with a disjunctor cell between each. Conversion of mycelial to spherule form (necessary for accurate identification) can be induced in culture. Endospores may remain close together following spherule wall rupture, causing confusion with the yeast form of Blastomyces dermatitidis.

Growth characteristics: Isolation involves inoculating the clinical material onto IMA agar, BHI agar with 10% sheep blood and a medium containing cycloheximide and incubating at 30°C. Cultures should be kept 4 weeks before considered negative, despite the fact it is usually fast-growing.

Common/important pathogens: