Valley fever is spreading. It is becoming more prevalent and traveling to new locations. The southwest is a perfect habitat for the fungi that causes valley fever, and because of this, those who live here and those who visit here need to know of the dangers and the signs.

What valley fever is

Valley fever, or coccidioidomycosis, is a fungal infection caused by soil-borne fungi called Coccidioides immitis and C. posadasii. Scientists first discovered Coccidioides in the 1800s, labeling it a parasite before reclassifying it as a fungus; and the first known valley fever infection occurred in 1892 in humans¹

Where valley fever is

Historically, Coccidioides exists endemically in parts of Arizona, California, Nevada, New Mexico, Texas, Utah, Mexico, and Central and South America²,³. Recent research shows the geographic distribution of the fungus is expanding, citing climate change creating optimal soil conditions as partially responsible¹. The fungus has recently been discovered for the first time in eastern Washington, Oregon, and Utah. 

A soil survey² published in 2021 shows soil properties that are most suitable for this fungus are low moisture, warm temperature, sandy, and high salinity (level of soluble salt). Though it needs some moisture to grow, Coccidioides lives in these optimal warm and dry conditions and lies dormant within soil for long periods. Landscape and climate contribute to soil properties, and the presence of Coccidioides can fluctuate based on these.  

Who valley fever affects

Valley fever can infect many animals including humans, dogs, cats, livestock, reptiles, and marine animals. It is most common in humans and dogs. According to the Centers for Disease Control and Prevention, it can affect people of any age but is most common in those over 60 years old.


How dogs contract valley fever 

Valley fever is not contagious and is not transmittable between humans, between animals, or between humans and animals. When something disturbs soil that contains the fungi (this can be anything: dust storms, construction, earthquakes, recreational activity, running, digging) spores become airborne. 

Once inhaled into the body, spores transfer into spherical cells and then multiply and spread¹. Spores spread either hematogenously (via bloodstream), which is most common, or through the lymphatic system. 

What the disease does 

When localized in the lungs, valley fever causes mild pulmonary disease or can develop into more severe pneumonia. Once disseminated (moved beyond the lungs), the disease can have various effects on the body depending on where it spreads. 

In the central nervous system it can cause seizures and behavioral changes. In the eyes, the disease can cause inflammation and pain, and hazy, weepy, red, and sunken eyeballs. Affected bones can suffer inflammation and lesions. Valley fever can cause inflammation of the heart as well as fluid accumulation, either of which can result in heart failure. Also possible are liver and kidney problems and skin lesions.

Symptoms of valley fever

Symptoms in healthy adult dogs can be mild, and some dogs may not become ill at all as their immune systems are able to successfully eliminate the disease. Dogs that are young, old, or immunocompromised are the most susceptible to becoming ill after exposure. Symptoms depend on the spread of the disease. When localized, valley fever symptoms can include dry cough, fever, decreased or lack of appetite, lethargy, and depression. Once disseminated, symptoms of valley fever may also include lameness, swollen/painful joints, weight loss, eye infection/inflammation, seizures, and skin lesions. 

Diagnosing valley fever

Valley fever symptoms can look like those present in other illnesses. When symptomatic dogs live in (or have traveled to) areas known for valley fever, veterinarians take this into account. Titer tests use blood samples to check for Coccidioides antibodies. Further diagnosis may include a complete blood count and radiographs. 

Treatment for valley fever

Treatment for valley fever depends on the severity of the disease. Dogs with mild cases may only need antifungal medication, though it is a long-term treatment of 6-12 months. Further antibody tests determine when a dog no longer requires antifungal treatment. Dogs with more severe cases may require lifelong antifungal medication. Fortunately, most dogs treated for early or mild cases have good prognoses. However, relapse is common, and dogs should be monitored throughout their lives.  

Some cases may require supportive care such as IV fluid treatments and oxygen therapy. Dogs with disseminated valley fever may require surgery for heart failure or to remove painful, infected eyes. Veterinarians may also administer antibiotics for secondary infections and steroids.

To conclude, valley fever is a disease that is becoming more common. Dogs spend much of their lives with noses to the ground, and those that live and play in arid locations are at increased risk for the disease. If you notice symptoms such as coughing, appetite change, or lethargy that may indicate an infection, talk to your veterinarian right away. Quick action can prevent severe disease. 



  1. Crum NF. Coccidioidomycosis: A contemporary review. Infectious Diseases and Therapy. 2022;11(2):713-742. doi:10.1007/s40121-022-00606-y
  2. Dobos RR, Benedict K, Jackson BR, McCotter O. Using soil survey data to model potential Coccidioides soil habitat and inform Valley fever epidemiology. PLOS ONE. 2021;16(2):e0247263. doi:10.1371/journal.pone.0247263
  3. CDC. Valley Fever Maps. Centers for Disease Control and Prevention. Published May 21, 2020. Accessed October 13, 2023.


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