Valley Fever in Dogs: Diagnosis and Treatment
Our friend Jodie over at Happy Dog Phoenix recently asked me about the health risks associated with summer dust storms. Answering her question got me thinking about Valley Fever. Most dog owners in Arizona have heard about this disease. This should come as no surprise, since one study estimates that nearly four out of every 100 dogs living in Maricopa and Pima counties will get sick from this disease each year. On the up side, the same study showed 70% of dogs that are exposed to Valley Fever don’t get sick.
Valley Fever is caused by a fungus called Coccidioides immitis; we call it “Cocci” in veterinary slang. Cocci is a mold that grows in the soil. When it matures, it sheds microscopic spores that are inhaled when dogs dig, sniff holes in the desert, or are exposed to blowing dust during a haboob. Signs of infection are non-specific. This means many different diseases can cause the same symptoms: lack of energy, poor appetite, weight loss, cough, fever, limping, and seizures. This is why Arizona veterinarians start thinking about Valley Fever as soon as they meet a dog that’s “ADR” (more slang… “ain’t doin’ right”).
Valley Fever is usually diagnosed with blood tests and X-rays. The blood test for Valley Fever detects antibodies against the fungus. Antibodies are proteins the immune system makes in response to a foreign invader. The test isn’t perfect, though. Those 70% of dogs that get exposed? Yeah, they make antibodies, too, so many dogs test positive even though they aren’t sick. And some dogs with Valley Fever don’t make any antibodies and test negative even though they’re infected. That’s why a full blood panel and X-rays are so important. Valley Fever is diagnosed based on a body of evidence: history, symptoms, a general blood panel, X-ray results, AND a Valley Fever test. If everything else supports the diagnosis despite a negative Valley Fever test, we’ll often start treatment and see how the patient responds. If they get better, chances are they DO have Valley Fever, no matter what the test says.
Most cases of Valley Fever respond well to treatment with an antifungal drug like fluconazole. Treatment takes several months in most cases, but the availability of generic medication has made treatment very affordable over the last 10 years. We usually treat for three to six months before repeating the Valley Fever test. A decreasing antibody level and vanishing symptoms generally indicates that the patient is responding to treatment. Antifungal drugs don’t kill Valley Fever, though; they just stop the fungus from growing. It’s up to the patient’s immune system to kill the disease. In some cases, the body isn’t up for the job; these dogs may need lifelong treatment. Some dogs die despite treatment, but thankfully this is the exception rather than the rule.
Preventing Valley Fever is tough. There’s no vaccine, and treating the soil is impractical. Reducing activity that generates dust (like digging) and sniffing in rodent burrows, as well as keeping dogs indoors can all reduce exposure. Grass and deep gravel, which reduce dust, can both limit exposure to the fungus, which can live up to 12 inches below the surface. Dogs that roam over more than one acre of land and those that spend 80% or more of their time outdoors are five to six times more likely to be infected.
Nearly every part of the United States has a unique fungal disease that affects pets; Valley Fever is ours. It’s as Arizonan as the saguaro and rattlesnakes, and it’s here to stay, so be on the lookout for symptoms and do what you can to limit your dogs’ exposure.