Valley fever is not contagious. It does not spread between people, from people to animals, or from animals to people. Every case of valley fever is acquired the same way: by breathing in fungal spores from contaminated soil or dust. You cannot catch it from a cough, a handshake, or sharing a room with someone who has it.
Why Valley Fever Cannot Spread Between People
The fungus that causes valley fever, called Coccidioides, exists in two very different forms depending on its environment. In soil, it grows as a mold that breaks apart into tiny spores, each only 2 to 4 micrometers wide. These spores become airborne when wind, construction, farming, or any soil disturbance kicks up dust. Inhaling even a small number of spores can start an infection.
Once inside the lungs, the fungus undergoes a dramatic shape change within 8 to 24 hours. The small barrel-shaped spores transform into larger round structures called spherules. This is the tissue form of the organism, and it is not infectious. When someone with valley fever coughs, sneezes, or has a draining skin lesion, what comes out is this tissue form, not the airborne spore form. That biological switch is the reason valley fever is a dead end for person-to-person transmission. The Valley Fever Center for Excellence at the University of Arizona confirms that even the fluid from open skin lesions is not considered infectious.
How People Actually Get Valley Fever
Nearly all infections begin in the lungs after inhaling spores stirred up from dry, dusty soil. The fungus lives in the ground across the southwestern United States, parts of Washington state, Mexico, and Central America. Arizona and California account for the vast majority of U.S. cases. In 2023, Arizona reported roughly 11,000 cases and California about 9,000, contributing to a national total of over 21,000 reported infections.
Activities that disturb soil raise the risk significantly. Construction, excavation, farming, off-road driving, and even natural dust storms can release spores into the air. You don’t need prolonged exposure. A single strong gust carrying contaminated dust can be enough.
What It Looks and Feels Like
Symptoms typically appear one to three weeks after breathing in the spores. The infection often mimics a bad cold or the flu: fatigue, cough, fever, shortness of breath, headache, and muscle aches. Some people develop a rash on the legs or upper body. Because these symptoms overlap so heavily with common respiratory illnesses like the flu or pneumonia, valley fever is frequently misdiagnosed at first, especially in people who don’t realize they’ve been in an area where the fungus lives.
About 60% of people who inhale Coccidioides spores never develop symptoms at all. Their immune system handles the infection silently. Among those who do get sick, most recover on their own within weeks to months. A small percentage develop a severe or chronic form that can spread beyond the lungs to bones, joints, skin, or the membranes surrounding the brain. People with weakened immune systems, pregnant women, and people of Black or Filipino descent face higher risk for these serious complications.
If Your Pet Has Valley Fever
Dogs are highly susceptible to valley fever, especially in Arizona, and owners understandably worry about catching it from a sick pet. You cannot. A dog with valley fever acquired the infection from the same soil you walk on, not from another animal. If multiple pets or family members in the same household develop valley fever, it means they were all exposed to the same contaminated environment independently. Coughing, drooling, and even draining wounds on an infected dog do not pose a transmission risk to you or other animals.
The Rare Exception: Organ Transplants
There is one narrow scenario where valley fever has passed from one person to another: organ transplantation. A handful of cases have been documented in which a donor unknowingly carried the fungus, and recipients developed coccidioidomycosis after receiving the transplanted organ. In one reported case series, a single donor’s organs went to five recipients, and three of them developed evidence of infection. These cases are exceptionally rare and represent a fundamentally different mechanism from casual or airborne spread. Transplant teams in endemic areas now screen for this possibility.
Reducing Your Risk in Endemic Areas
Since every infection comes from inhaling spores in dust, prevention centers on minimizing dust exposure. If you live in or travel to the southwestern U.S., a few practical steps can lower your risk:
- Avoid outdoor activity during dust storms or high winds. If you’re caught in one, stay in a vehicle or building with windows closed.
- Wet the soil before digging. Continuously dampening dirt during yard work or gardening keeps spores from becoming airborne.
- Use air conditioning with good filtration indoors. Keeping windows shut on windy days helps as well.
- Wear a respirator for heavy soil disturbance. Standard cloth masks offer limited protection against particles this small. NIOSH-certified respirators, properly fitted, are what occupational health guidelines recommend for workers doing manual digging or earthmoving in endemic areas.
The CDC also advises outdoor workers to stay upwind of any digging, change clothes and shoes before leaving a dusty worksite, and wash equipment before moving it to a new location. These measures won’t eliminate risk entirely, since spores can travel miles on the wind, but they meaningfully reduce the amount of dust you inhale during the highest-risk activities.