Valley Fever on the Rise

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Valley Fever on the Rise | Dr. Jean Dodds

The Basics

  • Valley Fever (also known as coccidioidomycosis) is caused by the fungi Coccidioides immitis and posadasii.
  • Coccidioides spp. lives in the soil in predominately semi-arid climates such as Southwestern United States, Southeastern Washington State, Central and South
  • When the soil is disturbed, the fungus can break apart and its spores become airborne. When inhaled, Coccidioides spp. can cause Valley Fever in people and animals. It is especially dangerous and can be fatal when infection occurs during pregnancy.
  • Rare transmission can occur from an organ transplant, if the organ donor had Valley Fever; inhaling spores from a wound infected with Coccidioides spp., and even contact with objects (such as rocks or shoes) that have been contaminated with Coccidioides spp..
  • While many animals like cats and horses are susceptible to Valley Fever, the disease particularly affects dogs.
  • Early symptoms of Valley Fever in dogs: coughing, fever, rashes on skin and extremities, weight loss, lack of appetite and reduced energy.
  • Can develop into pneumonia.
  • Disseminated Valley Fever symptoms: lameness or swelling of limbs, back or neck pain (with or without weakness/paralysis), seizures and other manifestations of brain swelling, soft abscess-like swelling under the skin, swollen lymph nodes, non-healing skin wounds that ooze fluid, eye inflammation with pain or cloudiness, unexpected heart failure in a young dog, swollen testicles.
  • Treatment for dogs involves prescribed antifungal medications for 6-12 months. Dogs with disseminated Valley Fever usually require longer courses of medication. If the central nervous system is affected, lifetime treatment with medication is typically needed to keep symptoms from recurring.

The Big Picture

Let’s step back a second and look at Southeastern Washington state, as Valley Fever was only recently discovered in this regional outlier. The distance from pretty much the center of Valley Fever’s highly endemic area, Maricopa County, Arizona, to Walla Walla County, Washington is almost 1,300 miles. Even if we map from suspected endemic Esmerelda County in Nevada to Walla Walla County, the distance is over 750 miles.

How did the Coccidioides spp. fungus get to Washington state?

Dr. Jack Rogers, a mycology professor emeritus at Washington State University, speculates, “Changing weather conditions, population sprawl that disrupts the soil and a possible rodent host moving northward in search of habitat could explain Cocci’s presence in Washington.” Tom Chiller, an expert from the Centers for Disease Control and Prevention (CDC), would agree that population sprawl leading to soil disruption is probably the case, but that theory supports his contention that Coccidioides spp. has always been there. The scary thing is: we really don’t know how Coccidioides spp. got there or if it was already there.

While experts debate whether Coccidioides spp. is spreading or intrinsic to an area, experts and the CDC postulate – almost affirmatively – that the ongoing dramatic changes in climate are causing more cases of Valley Fever in humans and dogs. The CDC states:

“Coccidioides spp. is thought to grow best in soil after heavy rainfall and then disperse into the air most effectively during hot, dry conditions. For example, hot and dry weather conditions have been shown to correlate with an increase in the number of Valley Fever cases in Arizona and in California. The ways in which climate change may be affecting the number of Valley Fever infections, as well as the geographic range of Coccidioides spp., isn’t known yet, but is a subject for further research.

Although most cases of Valley Fever are not associated with outbreaks, Valley Fever outbreaks linked to a common source do occasionally occur, particularly after events that disturb large amounts of soil. Past outbreaks have occurred in military trainees, archeological workers, solar farm workers, and in people exposed to earthquakes and dust

Climate change deniers may state that severe weather changes are not directly correlated to the increased diagnosis of Valley Fever, but rather it’s the increased awareness on the part of physicians and veterinarians to test for the disease. We do not disagree that awareness is a vital component for proper diagnosis, but do believe weather is also a crucial and vital component.

Yet, beyond weather and awareness, what else could be causing a difference between infection and illness?

We have written extensively about how two dogs could be in the same environment and exposed to the same conditions, but one contracts something and the other does not. In terms of Valley Fever, the University of Arizona Valley Fever Center of Excellence (VFCE) conducted a study in 2005. Their results affirm this scenario.

Incidence of Infection Study in Dogs

VFCE enrolled dogs from veterinary practices in Pima and Maricopa counties in Arizona. The researchers’ analysis demonstrated that dogs raised from birth in these Arizona counties have a 28% chance of being infected with the Coccidioides spp. fungi by two years of age. The probability of infection is 11% in the first year of life and 17% in the second year of life.

Dogs raised from birth in Pima or Maricopa county have a 6% probability of becoming sick with Valley Fever by 2 years of age: 2% in the first year and 4% in the second year.

From these results, the researchers estimate that about 4% of dogs will become sick with Valley Fever on an annual basis.

70% (42/60) of the dogs in this study had positive tests but were not sick from the infection. While the researchers believe that most of these subclinically infected dogs go on to become permanently immune, they would have liked to follow the blood test positive, healthy dogs for several more years to determine if the infection would flare into illness in the future.

In terms of humans, the CDC states that anyone at any age is at risk, but that common at-risk human populations are 60 years and older. Importantly, pregnant women, people with diabetes, and people with weakened immune systems are at higher risk of developing severe forms of Valley Fever.  

Additionally, we do know that people who work outside in professions such as construction or agriculture are at higher risk. But, is this population at higher risk due to the density of fungal dust, exposure in terms of length of time, weakened immune systems. or all of the above? We just do not know.  

For dogs, the VFCE is conducting very important research regarding the immune response to Valley Fever as well as in developing a vaccine.

Yet, could something else besides, or along with, the immune system be contributing to the seemingly randomized rate of Valley Fever illness in dogs?

A different research study, the Canine Valley Fever Project (CVFP), hypothesizes that epigenetics is also involved with the development, progression and severity of Valley Fever infections in pets and people.

The simplest definition of epigenetics is “on top of” genetics. It refers to external modifications to DNA that turn genes “on” or “off.” These modifications do not change the DNA sequence, but affect gene expression. So, environment, exercise, food, etc. all influence gene expression, which could trigger illness or suppress it.    

The formal study objectives of the CVFP study are:

To evaluate a dog’s breed, nutrition, health, environment, symptoms and disease resistance as compared with serology and hematology test results.

  • To better assess the number of dogs that are healthy but considered exposed to the Cocci organism or asymptomatic.
  • To obtain more accurate data on titers as compared to the severity of infection.
  • To stage and better formalize the standard of care across the board.
  • To provide faster and more efficient diagnosis of Valley Fever.
  • To study disease reduction as compared with drug protocols, diet and other lifestyle factors.
  • To increase awareness in pet owners and reduce misdiagnosis in the veterinary community.
  • To develop a registry and teaching tool to better serve both.

CVFP is actively looking for voluntary participants from around the United States. Even if your dog has never been to an endemic state, the information will help provide a baseline. Pet caregivers will need to complete a detailed questionnaire throughout the duration of the study. This questionnaire will help determine numerous significant and correlating factors regarding disease manifestation and management.

As an incentive and reward for participation, pet owners that enroll will be able to purchase discounted Valley Fever testing at

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843


“Canine Valley Fever Project.” Canine Valley Fever Project,

Coccidioides. Centers for Disease Control and Prevention, 22 May 2017,

“Valley Fever in Dogs.” University of Arizona Valley Fever Center for Excellence,

Weiford, Linda. “Illness-Causing Fungus Spreads to Washington State.” WSU Insider, Washington State University, 5 May 2014,

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