Coccidioidomycosis - also known as Valley Fever

Coccidioidomycosis was first described about 100 years ago in Argentina. It presents as a flu-like disease caused by a fungus, (Coccidioides immitis), found in the soil in the South Western USA, Central and South America. Once fairly rare, incidence has increased dramatically in recent times; it is commonly found in people who are exposed to soil dust. A major outbreak occurred in the San Joaquin Valley during WWII after the building of several air bases disturbed the soil causing many airmen to become infected - hence it is often referred to as Valley fever. Earthquakes are also responsible for isolated outbreaks.

Most infected people are either asymptomatic or have a self-limiting illness, requiring a few days or weeks off work. However, it can be much more severe, especially in people of Asian origin, African-Americans, people with diabetes, immuno-supressed individuals, pregnant women and those with AIDS.


Initially, a headache, cough, high temperature, aches and pains and possibly a rash may develop in 50% of infected individuals. In more severe cases pneumonia, meningitis, skin ulcers, bone and joint infections (synovitis) occur and chronic infection may last up to 2 years.

Development of the disease

C. immitis grows as a mold just below the surface of the soil. When conditions are right, usually in late summer when the weather is dry, arthroconidia (the infective particles) are released into the air and enter the body via the respiratory tract. Once in the lungs each particle changes shape and produces thousands of spores, each of which is capable of spreading through the lung and reproducing in the same way, resulting in acute respiratory infection after about a week.


Drug treatment using fluconazole and itraconazole is generally considered to be the most effective, as is amphotericin B, althought the latter is toxic in large doses. The search for new and more effective drugs is a high priority, but a vaccine would be the ideal choice since immunity to C. immitis is lifelong.

One little known fact about Valley Fever, also known as Coccidioidomycosis, is that it can affect certain animals as well as humans. Both dogs and horses can become infected, however for unknown reasons cats seem to be immune to the disease. Dogs are much more susceptible to the disease than horses because they are lower to the ground and because they often dig in dirt, creating contaminated dust that can be inhaled. Once infected the animal cannot spread the disease to other animals or humans, but it may require immediate treatment.

There are two types of Valley Fever in animals, classified as either primary or disseminated disease. Primary disease is the initial infection and is only located in the lungs of the animal. Some dogs may appear healthy during this stage while others may have symptoms including a dry cough, fever, and lack of appetite. These symptoms are generally seen within three weeks of infection. Most healthy dogs are able to fight off the disease at this stage, however young puppies, older dogs, and ones with weakened immune systems often cannot fight the disease and it spreads. If the infection spreads to other areas of the body it is classified as disseminated disease. The most common area of infection are bones, which are never infected in humans. In rarer cases the disease can spread to the brain, causing seizures. Other symptoms at this phase include weight loss and limping. The dog may tire out easily or even have difficulty biting toys. This stage of the disease is rather serious and most dogs that are not treated will likely die.

Veterinarians diagnose valley fever in dogs by performing a blood titer looking for antibodies produced against the valley fever antigens. Once the diagnosis is confirmed the dog takes antifungal medication for anywhere from 6 months to a year or longer, until the antibody titers have gone down to normal levels. Some dogs with severe cases may require medication for the rest of their lives. The most common antifungal medication is ketoconazole, which is given twice a day with meals. This drug is reported to cause loss of appetite and people report that changing the pet’s meals can help with this. Newer drugs, including itraconazole and fluconazole, have fewer side effects but are much more expensive. Antifungal medications can cost several dollars per pill, and a complete treatment can be prohibitively expensive. Many people have found that pharmacies in Mexico offer the drug for a much more reasonable price.

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