Valley fever is a fungal infection that dogs get by breathing in spores from soil, most commonly in the desert Southwest of the United States. The fungus lives in dirt across Arizona, parts of California, New Mexico, Nevada, Utah, and Texas, and dogs are particularly susceptible because they spend time outdoors sniffing the ground. More than 90% of infected dogs recover with treatment, but the infection can become serious if it spreads beyond the lungs.
How Dogs Get Infected
The fungus responsible for valley fever grows as thin, fragile strands in desert soil. When the ground is disturbed by digging, wind, construction, or even just a dog walking through it, those strands break apart into microscopic spores that float into the air. Dogs inhale the spores through their nose or mouth, and the infection begins in the lungs.
Once inside the lungs, the spores transform into larger structures called spherules. These spherules keep growing until they burst, each one releasing hundreds of new particles that can each form another spherule. This cycle continues spreading through the lung tissue until the dog’s immune system recognizes and fights off the infection. In many dogs, that immune response is strong enough to contain the infection on its own, and the dog may never show symptoms at all. In others, the fungus overwhelms the body’s defenses and causes illness.
Valley fever is not contagious between dogs, or from dogs to people. Every case comes from breathing in spores directly from the environment.
Symptoms of Lung Infection
The earliest and most common form of valley fever stays in the lungs. Dogs with a primary lung infection typically develop a dry, persistent cough that doesn’t respond to antibiotics. Other signs include fever, loss of appetite, weight loss, and low energy. Some dogs develop these symptoms within a few weeks of exposure, while others take months to show any signs.
Some dogs fight off the infection without ever appearing sick. Others develop only mild symptoms that an owner might attribute to a passing bug. Because the early signs overlap with so many other illnesses, valley fever often isn’t the first thing that comes to mind, especially if you don’t realize your dog has been in an area where the fungus lives.
When the Infection Spreads
In some dogs, the fungus escapes the lungs and travels to other parts of the body. This is called disseminated valley fever, and it can affect bones, joints, skin, lymph nodes, eyes, the heart, and even the brain or spinal cord. Occasionally, a dog will skip noticeable lung symptoms entirely and only show signs of disseminated disease.
The most common sign of disseminated valley fever is lameness. The fungus has a strong tendency to settle in leg bones, causing swelling, pain, and limping. Beyond that, symptoms depend on where the infection lands:
- Bones and joints: Swelling of the limbs, back or neck pain, weakness, or partial paralysis
- Skin: Soft, abscess-like swellings under the skin or non-healing wounds that ooze fluid
- Lymph nodes: Visible swelling under the chin, near the shoulder blades, or behind the knees
- Eyes: Inflammation causing pain, redness, or cloudiness
- Brain: Seizures or other neurological changes
- Heart: Unexpected heart failure, particularly alarming in a young dog
Disseminated disease is more serious and harder to treat, so catching valley fever early, while it’s still in the lungs, makes a meaningful difference in outcome.
How Valley Fever Is Diagnosed
The primary diagnostic tool is a blood test that checks whether your dog is producing antibodies against the valley fever fungus. If the test comes back positive, it confirms your dog has been infected. The lab then measures a titer, which reflects how much antibody is circulating. The titer is reported as a ratio like 1:4, 1:8, 1:16, and so on, with higher numbers generally indicating more severe disease.
A low titer of 1:4 or 1:8 can show up in dogs that are infected but not visibly sick. Very high titers, reported as greater than 1:256, usually point to serious or widespread infection. That said, the titer isn’t a perfect gauge. Some very sick dogs produce low titers or even test negative, so veterinarians interpret the number alongside symptoms and other test results rather than relying on it alone.
Depending on the situation, your vet may also run chest X-rays to look for lung changes, take blood cell counts, or biopsy suspicious tissue to look for the fungus under a microscope. If a dog is having seizures or showing signs of paralysis, a CT or MRI scan of the brain or spinal cord may be needed to assess how far the infection has reached.
Treatment and What to Expect
Valley fever is treated with antifungal medications, most commonly fluconazole or itraconazole. These are oral drugs your dog takes daily, and they work by stopping the fungus from growing and reproducing. A third option, ketoconazole, is also used but less frequently. For dogs that don’t respond well to initial treatment, a second antifungal can sometimes be added to improve results.
Treatment is long. Plan on 6 to 12 months of daily medication for a straightforward lung infection. Dogs with disseminated disease affecting bones, skin, or organs typically need longer courses. The most demanding scenario is when the infection reaches the brain or spinal cord. About 80% of dogs with neurological involvement respond to medication, but most of them need to stay on antifungal drugs for the rest of their lives to keep symptoms from coming back.
Because these medications are processed by the liver, your vet will periodically run blood panels to check liver enzyme levels and make sure the drug isn’t causing damage. If your dog develops vomiting, loss of appetite, or yellowing of the skin or gums during treatment, those could be signs of liver trouble and warrant a prompt call to your vet.
Titers are also rechecked during treatment to track progress. A dropping titer is a good sign. Most vets want to see the titer fall to a low level and the dog remain symptom-free before stopping medication, since ending treatment too early risks relapse.
Prognosis and Recovery
The outlook for most dogs with valley fever is good. More than 90% respond to antifungal treatment and recover. Dogs with infections limited to the lungs tend to do best, often returning to normal activity within a few months of starting medication even though the full course continues longer.
Dogs with disseminated disease, particularly in the bones, generally recover too, but the road is longer and relapses are more common. Brain involvement carries the most guarded prognosis. While most dogs with neurological valley fever can be stabilized on medication, the commitment to lifelong treatment is real, and not all dogs respond.
Reducing Your Dog’s Risk
There is currently no vaccine for valley fever in dogs, so prevention comes down to limiting exposure to contaminated soil. If you live in or travel through the desert Southwest, a few practical steps can help. Avoid letting your dog dig in dirt, especially in undeveloped desert areas. Try to keep outdoor time shorter on windy, dusty days when spores are most likely airborne. If your yard is bare desert soil, ground cover like gravel, grass, or artificial turf reduces the amount of exposed dirt that can harbor the fungus.
None of these measures eliminate risk entirely. Dogs that spend any time outdoors in endemic areas can encounter the spores. The most important thing you can do is stay alert to the symptoms, particularly a cough that won’t quit, unexplained lameness, or sudden weight loss, and let your vet know your dog lives in or has visited valley fever territory.