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Valley Fever
(Coccidiodomycosis)

Randy Walker DVM

About Valley Fever...

Valley Fever (technically referred to as Coccidiodomycosis) is a disease caused by a fungus called Coccidioides immitis. This fungus is common in the soils around Sun Lakes (the Sonoran lowland desert region of Arizona) and can cause disease in both people and dogs.

How Does The Severity Of Valley Fever Compare Between Dogs And Humans?

It is generally recognized that Valley Fever usually causes a much more severe illness in dogs as compared to people. Whereas people often fight off the disease with little or no medication (or so I'm told), dogs often will not recover without medication. In people, Valley Fever usually remains localized to the lungs but in dogs it has more tendency to spread from the lungs to other organs of the body such as the bones, brain, or liver, especially in untreated cases.

What Are The Symptoms Of Valley Fever In The Dog?

Valley Fever (coccidioidomycosis) can take several forms in the dog and these are too numerous to describe all of them here. In the "classic" case of Valley Fever the patient usually has a moderate to high fever, has a cough, is lethargic, and is off food. It should be noted that we routinely see cases of Valley Fever which do not fit this classic pattern. The most common exception is that a significant number of dogs with Valley Fever will have little or no cough. Also, besides the lungs, Valley Fever can infect any organ of the body; mainly the bones, nervous system, liver, or skin. When Valley Fever sets up infection in the bones, lameness can occur. If Valley Fever infects the brain this can result in seizures, mental dullness or meningitis (inflammation of the brain) among other conditions.

How Does A Dog Catch Valley Fever?

As stated before, Valley Fever is caused by a fungus (Coccidioides immitis) which occurs in the soils of the desert southwestern U.S. (California, Arizona, New Mexico, and Texas) and is quite prevalent in the area where I practice. Both people and dogs become exposed to Valley Fever through inhaling the infectious spores of this fungus through the dust in the air. Valley Fever is not transmitted from animal to animal.

What Are The Chances That My Dog Will Be Exposed To Valley Fever?

Public health officials estimate that over 95% of people and dogs become exposed to Valley Fever ( through the dust in the air ) after coming to desert areas such as Arizona. In most people and most dogs, this results in a mild (often subclinical ) illness in which the affected individual often doesn't realize they are sick. In these cases the infection is limited to an isolated region of the lungs and the immune system keeps it in check. It's really only a small minority of individuals who get a generalized illness with Valley Fever. When a generalized illness occurs, it can be quite severe and often fatal, if untreated, especially in dogs.

How Is Valley Fever Diagnosed?

Valley Fever is first suspected on the basis of the history, physical examination, and also radiographs (x-rays) when indicated. Then Valley Fever is either confirmed or ruled-out through a blood test which looks for antibodies to the Valley Fever organism.

How Reliable Is The Valley Fever blood Test?

In the vast majority of cases the Valley Fever blood test is a highly reliable indication of infection. In some cases, however, the test can give either a false positive result (meaning that the test indicates that an active infection is present when it is not) or a false negative result (meaning that the test says that an active infection is not present when it really is) . False positives and false negatives can happen because of the way antibodies are produced and their life expectancy in the body. When a dog is challenged by an infectious agent ( in this case Valley Fever ) the dog produces antibodies toward that disease. It takes a certain length of time to produce enough antibodies to register on the test and so, if the blood sample is taken early in the course of the disease there may not be enough antibodies produced yet to give a positive result on the test (this is a false negative). On the other hand, after a disease has run its course the patient will still have antibodies toward that disease in the bloodstream for some time and for this reason a blood test will sometimes give a positive result on the test even though the patient is not currently affected by this disease (this is a false positive). It should be emphasized again that these false positives and false negatives are seen in a small minority of cases. Because false negatives do occasionally occur we sometimes repeat the blood test in 3 weeks if Valley Fever is suspected (in spite of a negative test).

What Is The Prognosis For Valley Fever?

Valley Fever in dogs varies from case to case with the main factors being (1) the type of organs affected and (2) the overall general health of the patient. In general, those cases where the disease is confined to the lungs do better than those in which it has spread to the bones. Of the cases that have spread to the bones, the prognosis is worse the more bones that are involved.

How Is Valley Fever Treated?

Here again this varies between dogs and people. People with Valley Fever often do not need treatment (or so I'm told) unless the disease spreads from the lungs. Dogs, on the other hand, often times will not recover unless they receive medication. The medication of choice for Valley Fever is Ketoconazole (Brand name: Nizoral) which is an antifungal medication in tablet form. Valley Fever in dogs is very serious and often times difficult to cure. For this reason we generally treat the patient with Ketoconazole (twice daily) for at least 6 to 9 months. If, after 6-9 months, the patient appears to be clinically recovered, we can then continue the Nizoral on a trial basis.

What Are The Drawbacks And Side Effects Of Ketoconazole?

The main general drawback to ketoconazole is that it is relatively expensive as far as dog medications are concerned. The main adverse side effect is that it decreases the appetite and can also cause an upset stomach in some patients.

Can My Cat Get Valley Fever?

Although it can occur on occasion, Valley Fever is quite rare in cats.


- Randy Walker DVM
Sun Lakes Animal Clinic
May 17,2004



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