Dear Doctors: I read that something called valley fever is getting to be more common here in Arizona on account of climate change. I’ve never even heard of it. Can you please explain what it is?

Dear Reader: The term “valley fever” refers to an infection caused by the fungus Coccidioides, or Cocci for short, which is found in the soil of certain arid regions. Its habitat includes the Southwestern U.S., as well as Mexico and Central and South America. The fungus has long been known to live in the soil in Arizona, Nevada and California. In fact, the disease gets its name from a severe outbreak of the illness that occurred in the 1930s in the San Joaquin Valley in central California. It’s also present in large swaths of Utah, New Mexico and Texas. Recent outbreaks of valley fever show that the fungus is edging into northern Colorado and southern Montana, and it has also made a geographic leap to south-central Washington state.

When soil that contains the valley fever fungus gets kicked up, the fungal spores become airborne. These are the microscopic particles that fungi use to reproduce, much like the seeds in plants. The spores can be freed whenever the soil is disturbed, as occurs during mining, building or agricultural activity, and in severe weather with high winds. You mentioned climate change, and it is suspected that increasingly dry conditions throughout the West are playing a role in the spread of the fungus.

When airborne, the minuscule Cocci spores are easily inhaled. In rare cases, infection can occur via a break in the skin. Symptoms begin to appear one to three weeks after exposure. The majority of people will have no reaction to the fungus, or they will develop mild symptoms that abate on their own. However, some people who become infected can become quite ill. Severity of illness has been linked to the number of spores that someone has inhaled. Although the initial site of infection is the lungs, the fungus can then travel throughout the body and cause a range of symptoms.

The onset of infection often begins with general fatigue and a persistent cough. As the fungus travels throughout the body, a skin rash or lesions can appear. People also experience headaches, joint and body aches, night sweats and shortness of breath. Symptoms may go away after a few weeks, or they can be intermittent, fading away and then reappearing. Diagnosis begins with a detailed report of the individual’s symptoms, travel history and medical history. Once valley fever is suspected, a blood test for Coccidioides antibodies or antigens will likely be performed. The fungus can cause pneumonialike illness in the lungs, so imaging scans, such as an X-ray or MRI, may be needed. In severe cases, a tissue biopsy may be used to see if the fungal infection has become systemic.

Treatment depends on the severity of infection and risk factors for more serious disease. These include pregnancy, diabetes and being immunocompromised. Treatment ranges from watchful waiting to the use of antifungal medication. Most people make a full recovery.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health. Send your questions to, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.

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