Medical Author: Charles Davis, MD, PhD
Medical Editor: Melissa Conrad Stöppler, MD
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.
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.
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