Valley Fever and Your Petsby PAC Staff on 05/22/12
Valley fever is a disease caused by the fungus Coccidioides immitis. This fungus grows in the soil of the desert southwest because it does well in alkaline soil, low elevations and a warm, dry climate. It is very easily aerosolized—blown up into the air as dust—and spread via the wind. Construction or animals digging can disturb it, but even indoor cats are susceptible to it being pulled in through the air conditioning. A previous study done by the geology department at the U of A showed that valley fever infections have been found all over the Tucson area with a very slight increase in areas that have higher rainfall (which allows more fungal spores to grow). It can affect most species of domestic animals, but this article will focus on valley fever of dogs and cats.
The most common site of the body infected by valley fever is the lungs. However, it can disseminate—or spread to other parts of the body—and infect the bones, skin, eyes, brain, or spine/spinal cord. In very rare cases, it can affect the heart muscle, scrotum/testes, or the gastrointestinal tract.
The most common clinical signs are fever, lethargy, decreased appetite, coughing, and weight loss. These correspond to the most commonly infected primary site, the lungs. Other clinical signs correspond to the body system infected: limping for bone infections, open/weeping sores in the skin, inflammation in the eye, seizures or other neurologic abnormalities in the brain, neurologic abnormalities (weakness of the limbs, knuckling over, etc) and pain over the spine if the spine or spinal cord are affected. It is so common in our area that for any animal that is acting sick, especially ones with more vague signs, I put valley fever on the list of possibilities.
Valley fever is most commonly diagnosed by a combination of history, clinical signs, blood work and x-rays (in some cases, direct sampling of the tissue, especially the skin or bone, may yield organisms). The classic appearance on the white blood cell count (WBC or leukogram) is an increased white blood cell count because of the inflammation characterized by two different types of white cells. The valley fever titer is an antibody test, so it only checks for the body’s response to the disease, not if the disease is actively present or not. Elevated titers are usually indicative of disease, but the “art of practice” comes in with lower titers---are these exposure to the organism but not infection or true disease? These titers have to be considered in light of clinical signs, supporting lab tests, x-rays, etc. However, we do occasionally empirically treat dogs (and cats) that we have a strong suspicion have the disease, but may test negative, with fluconazole and an anti-inflammatory.
Treatment most often consists of fluconazole. This is the safest and most effective antifungal medication. In my experience, it also seems to be the best tolerated. In rare cases where valley fever does not respond to fluconazole, we will refer dogs to internal medicine specialists for liposomally encapsulated amphotericin B treatments. This is quite expensive and can often require many treatments.
It is important to realize with valley fever that unless an infection is confined solely to the lungs, valley fever, in my opinion, can never be completely cured. In infections in any other site of the body, these dogs must be on some lifetime maintenance dose of medications. In bone cases, this can commonly be as little as three times a week or as often as once a day. So it is important to never stop the drug in those cases, as it can come back worse and disseminate or spread to other parts of the body.
It is also important to track the progress of treatment success by repeating valley fever titers (as well as other supporting clinical lab data if that was initially abnormal) to ensure they are declining. I also recommend rechecking annual titers in lung cases, because I have seen a few of these turn out to have valley fever in other sites that were not initially apparent.
Also, immunosuppressants such as prednisone should be avoided in these patients (especially if someone has stopped the fluconazole), as it could allow the infection to more easily disseminate.Please don’t hesitate to schedule an appointment to discuss valley fever concerns with myself or any of our doctors here at Pantano Animal Clinic.