Coccidioides immitis Coccidioides immitis causes the disease coccidioidomycosis, which is most prevalent in the hot, dry regions of the Southwest. This microorganisms is dubiously assigned to the fungi, but differs from them in that it reproduces by a process of endogenous spore formation. Estimates are that 20-40 million people in the Southwest have had coccidioidomycosis. Dark-skinned individuals, of any background, are ten times more susceptible to this disease.
Transmission occurs by inhalation of the spores and no direct transmission from animals occurs.
The natural reservoir is the soil, and dust storms can induce infections, making this one of the only airborne diseases that man can contract outdoors. During the summer the sun sterilizes the soil, but this fungi survives in burrows. Spore Size 1-3 microns dia.