Valley fever in amimals is difficult to diagnose

Arizona Republic

Pet Doctor By Dr. Kevin Wright

DEAR PET DOCTOR: My dog has been sick for several months and only now did my veterinarian diagnose valley fever as the cause. Why did it take so long for him to come up with that answer?

DEAR READER: If you live in the lower Sonoran Desert, you and your pet are being exposed to valley fever on a regular basis. The fever is caused by a fungus with the tongue-twisting name of Coccidioides immitis. The disease also is called coccidioidomycosis, yet another reason most people choose to call it by the simpler nom de plume of valley fever.

Anywhere you see creosote bushes growing; this fungus is lurking in the soil. It dies if exposed to freezing temperatures and goes dormant during hot, dry conditions. Deep in the soil, however, the fungus avoids these temperature extremes and thrives.

During the monsoon season, the combination of rain and warm temperatures starts the fungus growing. Dust storms suck up dirt laden with fungal spores and spew them far and wide. These particles, called arthrosproes, hang in the air for hours or days.

Warm-blooded mammals such as pets and humans breathe in these arthrospores and, wham, they've got the valley fever. It takes only 5-10 arthrospores to infect susceptible dogs. And guess what? Every time a dust storm passes by, they've probably inhaled a few. What happens next? Well, the immune system in most dogs and people successfully fights the fungus.

Your dog may have a mild and brief fever, cough and mope around the house. Then, just as you are getting ready to go to the vet, your dog is once again bright-eyed and bushy-tailed, so you cancel the appointment. In this case, valley fever goes undiagnosed, thanks to your dogs appropriate immune response.

The lucky dog remains immune for a long time, probably boosted by inhaling new arthrospores each summer, and may never again show signs of infection. Unfortunately, about 10 percent of dogs are not so successful in combating valley fever on their own, and the fungus spreads into the brain, spinal cord, bone, joints liver, kidney and other organs.

Consider valley fever any time a dog has ongoing fever, lameness, coughing, poor appetite, weight loss, weakness, vision or hearing problems, or almost any other chronic problem. It can be difficult to detect fungal elements in mucus, spinal fluid, joint fluid or other samples, and many susceptible dogs don't produce enough antibodies for the blood test to work.

This means dogs with valley fever may test as if they don't have it. Diagnosing the disease can be quite frustrating, as its signs mimic a thousand other diseases. Often a dog is treated for it because nothing else matches the combination of signs and lab work. Valley fever takes up to 12 months to treat, and treatment is expensive. In addition to the cost, the antifungal drugs can cause serious side effects.


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