Valley Fever Causes

Humans and animals catch Valley Fever by breathing fungal spores that grow in undisturbed soil. Spores are lifted into the air from naturally occurring winds, dust storms, earthquakes, and other activities natural and man-made that disturb the top few inches of soil. Once in the air, the spores can travel miles infecting those in its path. During the 1977 dust storm in Bakersfield, several hundred cases as far north as Sacramento and the San Francisco Bay were identified.

Soil Phase (Mycelial)

The medical name for Valley Fever is coccidioidomycosis – often called cocci for short.  The name of the fungus  is Coccidioides immitis or Coccidioides posadasii.  In soil (mycelial phase) the fungus grows in long branching chains that can be the source of new infections in humans and animals for months to years.  In Kern County, rain during late winter and early spring causes the fungus to germinate and grow in undisturbed soil.  When temperatures rise, the Valley Fever fungus has the unique ability to form spores which then can survive the dry, hot summers. When naturally occurring winds disturb the soil, spores become airborne where humans and animals inhale the spores and become infected.

Human Phase (Spherule)
Ruptured Spherule

Once the fungus enters a human or animal it changes to a new form called a spherule. The change from the soil form to the spherule form typically occurs in the infected person or animals lungs.  The spherule will continue to grow in size by producing more fungus within the structure.  Once the spherule reaches its maximum size, it then breaks open releasing more infectious particles that can travel throughout the rest of the body.  This cycle will continue until the immune system gains control of the growth and replication of the spherules.

Most humans and animals control the growth and replications in the lungs and lymph nodes behind the lungs.  If the spores travel outside the lung and lymph nodes behind the lungs and establishes an infection, the case is referred to as disseminated.  For more information about the types of disease Valley Fever causes in humans and animals, see the page on signs and symptoms of Valley Fever.