Coccidioidomycosis, often referred to as “Valley Fever,” is an uncommon but extremely severe disease in cats, dogs and people that develops after inhalation (or less commonly, ingestion) of infectious microorganisms released by spores of the fungus, Coccidioides immitis. This fungus naturally occurs in soil and thrives in the hot, dry areas of the southwestern United States, Mexico and parts of Central and South America. Cats are particularly resistant to developing clinical disease as a result of infection by this microorganism; most cats exposed to the fungal spores never show signs of illness and develop immunity to the organism. Unfortunately, some cats will develop clinical disease, which can rapidly become life-threatening. When symptoms do develop in cats, they almost always include weeping skin lesions.
How Valley Fever Affects Cats
Coccidioides immitis thrives in hot, arid areas of the deep southwestern United States, Mexico and parts of Central and South America. Few felines exposed to the fungus succumb to clinical disease, but unfortunately some do. Cats that spend a significant amount of time outdoors in endemic areas are obviously at increased risk. Early signs of illness tend to be nonspecific and primarily respiratory, often starting with a dry, harsh cough. Cats are especially prone to developing weeping skin sores, much more so than dogs. Other clinical signs can include anorexia, weight loss, weakness and lethargy. As the fungal infection spreads, which can take months, affected cats may develop diarrhea, vomiting, lameness (from bone involvement), swollen joints, neck or back pain, seizures, vision abnormalities, emaciation and a fever that is unresponsive to antibiotics. Why most cats are able to resist clinical infection while others develop life-threatening disease is not well understood. Once a cat is infected systemically, the prognosis is guarded to grave.
Symptoms of Valley Fever
In cats, the Coccidioides immitis fungus attacks the skin. As a result, cats experience draining lesions on their skin throughout their entire body. In some cases abscesses will appear instead of lesions. In addition to draining lesions or abscesses, many cats also experience a loss of appetite and, as a consequence, weight loss. In very rare cases, the fungus will begin to affect the cat’s respiratory system and the cat may develop a chronic cough. If the fungus does spread to the respiratory system, it can then spread to other tissues in the body and cause lameness, eye symptoms, and neurological symptoms.
While some cats are able to ‘carry’ the fngus without any symptoms, it is believed that cats with lowered immune function are at a higher risk for developing coccidioidomycosis. Coccidioidomycosis symptoms in cats often progress slowly over a long period of time. Medical treatments for the condition are available, but if they are not given in a timely manner the disease can be fatal. If you live in a region where pets are at risk for developing coccidioidomycosis and your cat is displaying any of the above symptoms, schedule an appointment with your veterinarian as soon as possible.
Causes of Valley Fever in Cats
Valley Fever is caused by inhalation or ingestion of infectious microorganisms released by spores of the fungus, Coccidioides immitis. In the deep southwestern areas of the United States, particularly in arid desert regions of Arizona, California and Texas and less commonly in New Mexico, Nevada and Utah, this fungus persists naturally several inches deep in the soil of endemic areas, where it can survive high temperatures and low moisture. It is dormant during periods of drought. After rainfall, earthquakes or other causes of soil disturbance (such as demolition or other large land construction projects), the fungi rise to the surface, sporulate and become airborne. Inhalation of fewer than 10 of these microorganisms can cause clinical disease. Fortunately, few cats exposed to the fungal spores succumb to clinical disease. Older and immunocompromised cats seem to be at higher risk, as do those with poor nutritional support. Valley Fever cannot be transmitted between people and cats and is not contagious between cats. When it becomes disseminated throughout the body, it is considered one of the most severe and potentially fatal fungal diseases in companion animals.
Preventing Valley Fever in Cats
This disease cannot occur unless a cat has lived in or traveled through a region where Coccidioides immitis is endemic. Contaminated soil in those areas – especially during dust or wind storms after heavy rain – should be avoided if at all possible. There is no vaccine against coccidioidomycosis for either cats or dogs.
Treating Valley Fever in Cats
The therapeutic goals for this disease are preventing further dissemination of the microorganisms, eradicating the fungal organisms and improving or at least maintaining the patient’s quality of life. Most cats are treated as outpatients. Supportive care for these cats involves restricted activity until clinical signs of infection resolve. They should be fed a high quality, palatable diet with free access to fresh water at all times. If necessary, oxygen supplementation can be provided on an inpatient basis.
Diagnosis should be rapidly followed by oral anti-fungal therapy. The anti-fungal drugs currently available for feline treatment include itraconazole, ketoconazole and fluconazole, although of course with time newer medications may become available. Ketoconazole can be effective and is the least costly, but it carries more adverse side effects than the other two anti-fungals, including liver damage, vomiting and inappetance. Itraconazole is more expensive than ketoconazole and may or may not have fewer side effects. Fluconazole has the best penetration of the eye and central nervous system but is the most costly. Whichever anti-fungal medication is chosen by the attending veterinarian, it must be administered precisely in accordance with the veterinarian’s instructions. This will normally be twice daily, for at least one year. Long-term use of azole drugs can cause liver dysfunction, gastrointestinal upset and adverse skin reactions, so treatment must be closely and regularly monitored.
Unfortunately, clinical disease in cats typically involves systemic infection. The prognosis is guarded to grave.
Successful treatment is possible if the fungal infection is promptly and properly diagnosed, although treatment typically takes months to years to complete. Diagnosis of Valley Fever is complicated by the fact that most diagnostic laboratories regard the fungus as too dangerous to culture because of the significant risk of human infection. The prognosis for cats is not well documented. However, reports suggest that owners of clinically affected cats should be prepared for rapid systemic dissemination of the fungal infection that requires long-term treatment.