Coccidioides immitis

Shmuel Shoham, M.D.


  • Causative organisms and endemic regions
    • Coccidioides immitis: Primarily found in the Central Valley of California, but pockets are as far north as eastern Washington state.
    • Coccidioides posadasii: Primarily foundin the desert areas of Arizona, Texas, Utah, Mexico, and Central and South America
    • Both species can be found in Southern California
  • Dimorphic fungal characteristics [Fig 1]:
    • Environmental form: filamentous with septated hyphae that grow in soil. When a dry spell follows rain, the hyphae become brittle, and small (~3-5 μm in diameter) fungal particles termed arthroconidia break off, become airborne, and potentially inhaled.
    • Invasive form at 37°C: following inhalation or occasionally via percutaneous entry, arthroconidia transform into large (~60-75 µm in diameter) structures termed spherules that contain hundreds of small (~2-5 µm in diameter) structures termed endospores. When the mature spherules rupture, endospores are released, which can, in turn, form additional spherules [Fig 2].
  • Environmental conditions
    • Preferentially grows in regions of California, Southwest U.S. and parts of Mexico that have hot summers, moderate winters and little rainfall.
    • Isolated pockets of C. posadasii are also found in parts of South and Central America.
    • Growth of the fungus as far north as central Washington state has been described.
    • The environmental reservoir is suspected to involve rodents
  • Micro: grows readily on standard fungal media.
    • Coccidioides grown in culture can be a significant laboratory hazard and must be handled cautiously in an appropriate safety cabinet.
      • When submitting specimens, alert the micro lab if suspected.

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Last updated: June 13, 2024