Triggers Death in Dogs, Is It Found in Your Area?

Analysis by Dr. Karen Shaw Becker

valley fever in dogs

Story at-a-glance -

  • After monsoon season and intense dust storms, Phoenix-area veterinarians are reporting an increase in valley fever in dogs
  • Valley fever, or coccidioidomycosis, is a potentially deadly fungal disease that occurs in hot, dry climates; dogs are exposed by inhaling the soil-borne fungi
  • In Arizona, about 70 percent of dogs are able to fight off the infection; in infected dogs, symptoms can include fever, coughing, difficulty breathing, lethargy and lameness
  • Treatment depends on the extent of the infection and clinical symptoms, and can involve antifungal drug therapy for up to a year
  • In valley fever endemic areas, there’s no foolproof way to prevent infection; however, there are steps dog parents can take to reduce the risk of exposure

Recently, a local newspaper in Arizona alerted dog owners that the end of monsoon season was bringing an increase in cases of valley fever in dogs all over the Greater Phoenix area.1

The scientific name for valley fever is coccidioidomycosis, which is an infection caused by the Coccidioides immitis fungus. It's a relatively uncommon but potentially deadly disease that occurs in dry, hot climates in the western and southwestern U.S., especially Southern California, Arizona, southwest Texas, New Mexico, Nevada and Utah, as well as in Central and South America.

Coccidioidomycosis is also known as California fever, desert fever and most commonly, valley fever. The condition can affect many types of mammals, including humans. It occurs more often in dogs than cats. The condition is not zoonotic, meaning it can't be passed from animal to human or human to animal.

How Dogs Develop Valley Fever

The Coccidioides immitis fungus is found in upper layers of soil, but several inches deep where it can withstand high temperatures and lack of moisture. The fungus works its way to the surface after a rainy period or soil disturbance of some kind.

Once on the soil's surface, the fungus forms spores that are spread by wind and dust storms. Arizona's summer monsoons and haboobs (violent dust storms) create an ideal environment for the fungus to thrive and spread, which means most dogs in the state have been exposed.

Dogs acquire coccidioidomycosis from inhaling the soil-borne fungus, and those who are susceptible to the infection can become ill from as few as 10 fungal spores. In Arizona, estimates are that about 70 percent of dogs successfully fight off the infection. Unfortunately, the remaining 30 percent go on to acquire the disease and require long-term treatment with antifungal medications.

The infection starts in the respiratory tract and then frequently spreads to other body systems. In the lungs, the spores are round globules that exist as parasites until they grow big enough to break open, releasing hundreds of endospores that travel to other tissues, and continue the process of growing, rupturing and spreading throughout the body.

If the endospores get into the lymphatic and circulatory systems, they create a systemic infection. Coccidioidomycosis sets in from one to three weeks after exposure. Dogs who are outdoors a great deal are at highest risk — especially dogs with lots of space to roam. Large dogs seem more at risk, perhaps because they tend to spend more time outdoors than smaller dogs.

Symptoms to Watch For

Dogs whose immune systems are able to fight off the infection often show no symptoms, especially younger dogs. When symptoms are present, they can include:



Skin ulcers and draining sores


Swelling of bones or joints

Inflammation of the cornea or iris of the eye

Difficulty breathing

Significant weight loss and muscle wasting



Enlarged lymph nodes

Heart failure

It's not unusual for valley fever to spread throughout the body, affecting bones and joints, eyes, skin, liver, kidneys, central nervous system, cardiovascular system and reproductive organs (specifically the testes).

Cats usually don't exhibit the same symptoms as dogs do, and frequently show no symptoms at all until the infection has spread significantly. In cats, the deeper layers of skin tissue are more often affected, so symptoms like masses, abscesses and lesions with draining are more common in kitties.

Diagnosis and Treatment Options

As with any disease, early detection offers the best outcome for dogs with valley fever, so if you live where the infection is prevalent and your pet is showing possible symptoms, it's crucial that you get her to your veterinarian as soon as possible. Your vet will perform a careful physical exam and order a complete blood count, chemical blood profile and urinalysis. You'll need to provide a history of your dog's health and symptoms, including possible opportunities for exposure to the fungus.

Treatment of valley fever depends on the extent of the infection and clinical symptoms. If the condition is widespread, traditional treatment involves aggressive antifungal therapy for up to a year. Other drugs, including cough suppressants, may also be prescribed to treat individual symptoms.

In dogs who aren't responding well to drug therapy, a drug level measurement test can be performed to determine how well the medication is being absorbed.

The University of Arizona's Valley Fever Center for Excellence (VFCE) estimates valley fever infections cost Arizona dog owners $60 million per year in treatment expenses.2 The cost of the most commonly prescribed antifungal, fluconazole, is about $50 a month for smaller dogs, and can be in excess of $150 for large dogs. In addition, the necessary blood tests average around $200.

Integrative veterinarians often combine traditional antifungal therapy with more natural modalities like cytokine therapy, medicinal mushrooms, IV vitamin C therapy, hyperbaric oxygen therapy and ozone therapy. Some Arizona pet parents are also using CBD oil to reduce pain and inflammation in dogs with the disease.

Affected dogs should be fed a high-quality, nutritionally balanced, species-appropriate diet to help maintain body weight. Activity should be restricted until symptoms begin to subside, and antibodies should be monitored every three to four months until they return to a normal level.

Unfortunately, valley fever is one of the more dangerous fungal diseases, and the prognosis for most dogs is guarded. While many improve following a course of antifungal drug therapy, relapse is common.

Prevention Tips

Valley fever endemic areas are some of the fastest growing regions in the U.S., which means more pets (and humans) are being exposed to the fungus. If you live in one of those areas, there's really no foolproof way to prevent infection in your dog. To reduce the likelihood of exposure to the fungus, the VFCE recommends:

  • Avoiding activities that generate dust
  • Minimizing dog digging behavior
  • Preventing sniffing in rodent holes
  • Keeping dogs indoors more than outdoors

It's not useful to try to treat the soil because the fungus is found in spotty areas rather than in multiple large locations, and can live up to 12 inches deep in the ground. Ground cover, such as grass, deep gravel or another dust-controlling cover can reduce dust, which is beneficial.

If you don't live in a region where the infection is prevalent, but you and your dog hunt or travel or spend time in endemic areas and he begins to show symptoms of infection, let your veterinarian know he may need to be tested for valley fever.