Coccidioidomycosis in Dogs
My dog became very lethargic, stopped eating, and started coughing. My veterinarian told me she has “Valley Fever.” What is that and how is it treated?
Valley Fever is another name for a disease called “coccidioidomycosis.” Coccidioidomycosis is a fungal disease caused by the soil fungus Coccidioides immitis. Coccidioides immitis is found primarily in the southwestern United States, and is most common in Arizona, southern California, and southwestern Texas. It is not as common but still occasionally found in Nevada, New Mexico, and Utah. The organism grows down several inches in the soil, and can survive the high temperatures of the desert regions. During the rainy season, Coccidioides immitis can return to the surface and sporulate, allowing infective spores to be spread by the wind.
The early signs of coccidioidomycosis include fever, lethargy, lack of appetite, coughing, and joint pain. The dog may develop lameness and/or weakness, as well as back and neck pain. In severe cases, if the organism spreads throughout the body, becoming systemic, the dog may develop seizures or blindness.
Most dogs who develop coccidioidomycosis are typically young, possibly because this is the demographic that tends to be more active outdoors. Dogs who dig in the dirt or who spend time outdoors following a dust storm may also be a greater risk for exposure.
How did my dog get coccidioidomycosis?
Coccidioidomycosis occurs after inhalation of the fungus spores. In a susceptible dog, inhalation of fewer than 10 spores can cause illness.
How is coccidioidomycosis diagnosed?
Diagnosis of coccidioidomycosis in dogs can be challenging because the symptoms are not specific for this disease. The first wave of symptoms typically includes fever, coughing, and difficulty breathing. If the disease spreads to other parts of the body, the symptoms will depend on the tissues and organs that are involved. The dog may exhibit lameness, joint swelling, or swelling in bones. The lymph nodes may be enlarged. There may be nervous system dysfunction. The eyes may become inflamed, causing vision problems. Finally, the skin may develop sores that will not heal, or draining tracts. X-rays of the chest may demonstrate lung lesions, and X-rays of affected bones may assist in diagnosis.
"The most common way to diagnose
is by testing for antibodies to the organism."
While coccidioidomycosis can be definitively diagnosed via biopsy, the most common way it is diagnosed is by testing for antibodies to the organism.
How is coccidioidomycosis treated? How long will my dog have to be treated?
Most dogs with coccidioidomycosis are treated at home rather that in the hospital. Vigorous activity should be restricted until the dog begins to feel more normal and comfortable. This is a very serious illness requiring long-term treatment — for many dogs this means treatment for at least one year. There are several oral medications your veterinarian may choose from to treat this disease.
What sort of follow-up is required for dogs who are treated for coccidioidomycosis?
Dogs being treated for coccidioidomycosis will have repeated measurement of their antibodies to this organism. Levels are typically measured every 3 - 4 months, and need to be treated until their levels fall to less than 1:4. Regular monitoring of kidney and liver function may also be recommended. If needed, cough suppressants may be prescribed if severe coughing develops.
Unfortunately, coccidioidomycosis carries with it a guarded to grave prognosis, and while dogs may improve during medical therapy, relapses are common. Overall recovery from coccidioidomycosis has been reported at between 60% and 90%.
Why don’t all the dogs in Arizona have this disease?
Interestingly enough, despite the presence of Coccidioides immitis in the soil (and soil is everywhere), coccidioidomycosis is not very common, even in the endemic areas of the US. Asymptomatic infections may occur, in which dogs are exposed, but develop immunity without experiencing the signs of full-blown disease.
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