Valley Fever (Coccidioidomycosis)
Medical Author: Charles Davis, MD, PhD
Medical Editor: Melissa Conrad Stöppler, MD
What is valley fever (coccidioidomycosis)?
Valley fever (coccidioidomycosis) is a disease caused by fungi (Coccidioides
immitis and C. posadasii species) that in about 50%-75% of normal (not
immunocompromised) people causes either no symptoms or mild symptoms and those infected
never seek medical care; when symptoms are more pronounced, they usually present
as lung problems (cough, shortness of breath, sputum production, fever, and chest
pains). The disease can progress to chronic or progressive lung disease and may
even become disseminated to the skin, brain (meninges), skeleton, and other body
areas. The disease can also infect many animal types (for example, dogs, cattle,
otters, and monkeys).
Most microbiologists and infectious disease physicians prefer the name
coccidioidomycosis because the word describes the disease as a specific fungal
disease, and this term may replace valley fever in the future. This disease
has several commonly used names (valley fever, San Joaquin Valley fever,
California valley fever, acute valley fever, and desert fever). Other names get
confused with valley fever (for example, rift or African valley fever, which is
caused by a virus).
Coccidioidomycosis was first noted in the 1890s in Argentina; tissue biopsies
of people with the disease showed pathogens that resembled coccidia (protozoa).
During 1896-1900, investigators learned the disease was caused by a fungus,
not protozoa, so the term "mycosis" was eventually added to "coccidia." The
disease is often noted to occur in outbreaks, usually when soil is disturbed and
dust arises, and when groups of people visit an endemic region (such as San
Joaquin Valley or Bakersfield, California, and Tucson, Arizona, or parts of
southern New Mexico or west Texas) during late summer and early fall. The
disease is not transmitted person to person; it is acquired from the environment
via contaminated soil and dust. About 100,000 cases are diagnosed each year in
the U.S.
What causes valley fever (coccidioidomycosis)?
Coccidioidomycosis is caused by two species of fungi, Coccidioides immitis and
Coccidioides posadasii. Both are dimorphic (having mycelial and spore phases),
almost always acquired through the respiratory tract by inhalation. When viewed
microscopically, the mycelial form found in the soil has arthroconidia
(barrel-shaped asexual spores) attached to non-spore-forming rectangular
mycelium cells, usually alternating in a line. Once the arthroconidia are
inhaled, the fungus develops into 30-60 micron diameter spherules that are
filled with 3-5 micron diameter endospores. The large spherules then release the
endospores that continue the infection; microscopic identification of these
endospores in pus or tissue confirms the diagnosis.
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| Picture of Coccidioides immitis fungal organism |
Pictures of Coccidioides immitis and lung X-rays can be seen in the first and
third Web sites listed below.
Next: What are the symptoms of valley fever (coccidioidomycosis)? »
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