Valley Fever in Dogs
Credit: University of Arizona, College of Medicine Tucson
How Dogs Get Valley Fever
Valley Fever is caused by a fungus that lives in the desert soil in the southwestern United States.
Like people, dogs are very susceptible to Valley fever. Dogs primarily contract Valley fever in the low desert regions of Arizona, New Mexico and southwestern Texas and the central deserts of California. Dogs accompanying people traveling through these areas or wintering in these warm climates have about the same chance as their owners of being infected.
Dogs comprise the majority of Valley Fever cases in animals. However, other animals can get the disease as well. Cats, llamas, non-human primates, horses, zoo animals, and even wild animals have been reported with Valley Fever.
Approximately 6-10% of dogs living in Pima, Pinal, and Maricopa counties in Arizona will become sick with Valley Fever each year. The rate of illness in other Valley fever endemic locations is not known, but it is lower most places than central and southern Arizona.
Not all dogs who breathe in spores become sick. About 70% of dogs who inhale Valley Fever spores control them quickly. These dogs are asymptomatic and are probably immune to the disease afterwards. This is very similar to what happens in people.
The life cycle of Coccidioides
As part of its life cycle, the fungus grows in the soil and dries into fragile strands of cells. The strands are very delicate, and when the soil is disturbed – by digging, walking, construction, high winds – the strands break apart into tiny individual spores called arthroconidia or arthrospores. Dogs and other animals mainly acquire Valley Fever by inhaling these fungal spores in the dust and air. The dog may inhale only a few spores or many hundreds.
Once inhaled, the spores grow into spherules which continue to enlarge until they burst, releasing hundreds of endospores. Each endospore can grow into a new spherule, spreading the infection in the lungs until the dog’s immune system surrounds and destroys it. The sickness Valley Fever occurs when the immune system does not kill the spherules and endospores quickly and they continue to spread in the lungs and sometimes throughout the animal’s body.
Symptoms
The most common early symptoms of primary pulmonary Valley fever in dogs:
- Coughing
- Fever
- Weight loss
- Lack of appetite
- Lack of energy
Some or all of these symptoms may be present as a result of infection in the lungs. As the infection progresses, dogs can develop pneumonia that is visible on x-rays.
Sometimes the coughing is caused by pressure of swollen lymph nodes near the heart pressing on the dog’s windpipe and irritating it. These dogs often have a dry, hacking or honking kind of cough and the swollen lymph nodes can be seen on x-rays.
When the infection spreads outside the lungs, it causes disseminated disease. The most common symptom of disseminated disease in dogs is lameness; the fungus has a predilection for infecting bones of the legs in dogs. However, Valley fever can occur in almost any bone or organ of dogs.
Signs of disseminated Valley Fever can include:
- 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 under the chin, in front of the shoulder blades, or behind the stifles
- Non-healing skin wounds that ooze fluid
- Eye inflammation with pain or cloudiness
- Unexpected heart failure in a young dog
- Swollen testicles
Sometimes a dog will not have any signs of a primary infection in the lungs, such as coughing, but will only develop symptoms of disseminated disease, e.g., lameness, seizures. Very few of the signs of Valley fever are specific to this disease alone and your veterinarian will do tests and x-rays to determine that your dog’s illness is Valley fever and to rule out other causes.
Prevention of Valley Fever in Dogs
Currently, there is no sure-fire way to prevent Valley Fever in pets short of never residing in or traveling through the areas where the fungus grows. Valley Fever endemic areas are among the fastest growing regions in the country, which makes encounters of animals and people with the fungus a likely event.
Things you can do to reduce the likelihood of your dog’s exposure to the fungus: Avoid activities that generate dust, reduce digging behavior by dogs, prevent sniffing in rodent holes, and keep dogs indoors more than outdoors. Treating the soil is currently not practical as the fungus lives in spotty areas and can live up to 12 inches deep in the ground. Yard ground cover that reduces dust, however, is helpful: grass and deep gravel or other dust-controlling cover.
A vaccine is under development. It is possible a vaccine will be available in the future to prevent Valley Fever or make it only a very mild illness in dogs. Vaccination against Valley Fever would be very useful for animals traveling to places like southern Arizona and southern California as well as for those dogs that live in these places.
