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Valley Fever in Dogs — Signs and Treatments

Why this fungal disease is not always easy to recognize.

by Jamie Whittenburg, DVM
August 27, 2021
Dog standing on dry, gravel path near wildflowers
Stephen Morris / Stocksy

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As if pet parents didn’t have enough to worry about: dogs living in the southwest are prone to a unique disease called Valley Fever. According to Veterinary Information Network, it’s estimated that 60% of those infected with Valley Fever don’t show any symptoms. But for that other 40%, it’s another story.

Valley Fever is a fungal disease that is most common in humans and frequently affects dogs and other species.  Also known as coccidioidomycosis, it’s caused by a fungus called Coccidiodes immitis. Other common names for the disease are California disease, San Joaquin Valley Fever, and desert rheumatism.

The fungus that causes Valley Fever in dogs lives in dry soil. There are many areas in the United States where the fungus has been found in the dirt, including Arizona, California, Nevada, New Mexico, Texas, Utah, and Washington. The climate is an important factor in fungus transmission, as the spores will be found in arid, dry areas.

Valley Fever is unique in the fact that it can affect a wide range of species. The condition has been diagnosed in humans, dogs, cows, horses, deer, llamas, mules, apes, monkeys, tigers, kangaroos, wallabies, bears, otters, fish, and even dolphins.

Of all the animal species that can be affected by Valley Fever, dogs tend to be the most susceptible. It is normal for dogs to sniff the ground and dig in the dirt, but these behaviors can result in them inhaling the coccidiodes spores. Inhalation of the spores leads to a high rate of Valley Fever.

Symptoms of Valley Fever in Dogs

Initially, the spores are inhaled into the dog’s nasal passages and lungs. Here they become spherules. If the dog is a healthy adult with a well-functioning immune system, the spherules will be walled off, and the body will rid itself of them. These dogs rarely show any signs of illness.

In other cases, when a dog is very young, very old, or has a compromised immune system, the spherules grow larger and larger until they burst. When this occurs, they release large amounts of spherules that move on to infect other areas of the body. This cycle is how the disease progresses unchecked in dogs with weak immune systems. There are two forms of Valley Fever in dogs: localized and disseminated.

Localized infections are limited to the dog’s lungs. Signs include:

  • Cough

  • Fever

  • Lack of Appetite

  • Tiredness

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Disseminated infections occur when the fungus spreads from the respiratory tract to other areas of the body. Often, the skeletal system is affected, and the fungus attacks the bones and the joints. Signs include:

  • Lameness

  • Swollen joints

  • Heat in the joints

  • Loss of appetite

  • Tiredness

  • Fever

  • Weight loss

Any dog living in, or with travel history to, the regions where Valley Fever is common that exhibits these signs should be examined by a veterinarian as promptly as possible.

Transmission of Valley Fever

Coccidiodes immitis is a unique fungus in that it has the ability to survive dry weather by entering a spore phase. When the conditions are not dry, the fungus exists as a mold in the environment. Dry weather forces the fungus to sporulate, and it may stay in this form for years. When the dirt is disturbed by a dog through sniffing or digging, the spores are inhaled. Wind and rain can also cause the spores to become airborne, enabling them to be inhaled. Once inhaled into the dog, the spores change into the spherules that infect the dog as their host.

Because the inhalation of fungal spores causes this disease, there is no danger of human-to-human or dog-to-dog transmission. This means that Valley Fever is not a contagious disease (phew, some good news).

Diagnosing Valley Fever

Valley Fever should be suspected in all dogs that are exhibiting clinical signs and that live, or have traveled to, areas where the disease is common. A dog that may be infected should be seen by a veterinarian as soon as possible. Diagnosis of Valley Fever in dogs is made via a titer test which will determine if the dog possesses antibodies to the coccidiodes fungus. Dogs should also have complete blood work, a urinalysis, and chest x-rays to determine the extent of the disease.

Treatment of Valley Fever in Dogs

Treatment of Valley Fever in dogs consists of long-term oral antifungal medications. These medications are necessary for months to years, and the duration will be determined by the severity of the dog’s infection and the response to treatment. Because the drugs needed to treat this condition can have side effects affecting the liver and other organs, routine bloodwork will be necessary throughout treatment.

The most commonly prescribed medications for Valley Fever include ketoconazole, itraconazole, and fluconazole. The treating veterinarian will choose the most appropriate medication for the dog. Most dogs that start on antifungal medications show improvement in the first 14 days of treatment.

The prognosis for most dogs with Valley Fever is good, and it has been reported that more than 90% of dogs diagnosed with and treated for Valley Fever will survive. In general, the earlier the disease is diagnosed, and treatment is begun, the better the prognosis. Sadly, some dogs affected by the disseminated form, especially if they are severely immunocompromised, have a poor prognosis and will succumb to the disease. It is essential to continue the antifungal medications as long as necessary, or many dogs will relapse. Periodic blood tests to evaluate organ function, as well as fungal titers to determine the efficacy of the medication, are vital.

How to Protect Your Dog from Valley Fever

Hypothetically, dogs may be re-infected if they inhale more spores, but there is little research to prove this. Relapses are common, however. Long-term antifungals are necessary, and the length of treatment required will be determined through testing by your veterinarian. To help prevent Valley Fever, owners should do their best to avoid dogs inhaling fungal spores. This may be accomplished by keeping dogs indoors, walking dogs on leashes at all times, and limiting outdoor excursions to paved areas and sidewalks.

The good news is that many healthy adult dogs will clear Valley Fever on their own and will not require treatment. However, if a dog is ill with Valley Fever, a veterinarian must be consulted, and prescription antifungal medications will be necessary. It is a myth that garlic will cure Valley Fever. In fact, garlic is toxic to dogs and can lead to life-threatening anemia.

As always, if you are concerned about the health of your pet, please contact your veterinarian. The information provided in this article is for educational and informational purposes only and is not meant as a substitute for professional advice from a veterinarian or other professional.


Jamie Whittenburg, DVM

Dr. Jamie Whittenburg graduated from Kansas State University College of Veterinary Medicine (DVM). She opened her own hospital, Kingsgate Animal Hospital, in Lubbock, TX, and is a veterinarian writer for Senior Tail Waggers.