Causes of “Valley Fever” in Dogs
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 or Utah, the fungus Coccidioides immitis persists naturally several inches down in the soil. During periods of drought, the fungi exist in a dormant stage. Following periods of rainfall, the fungi sporulate and release many infectious stages of the organism called “arthroconidia,” that spread by wind, dust and rain storms. Release of spores in endemic areas is also commonly associated with earthquakes and demolition or other large land construction projects where substantial soil disruption occurs. Inhalation of even 10 or fewer of these highly infectious spores can cause clinical disease. However, many exposed dogs will not develop clinical signs; they may have asymptomatic infections with very mild, undiagnosed respiratory infection, or they may develop immunity without ever showing clinical signs.
Why some dogs are able to resist clinical infection while others develop life-threatening disease is not well understood in current circles of veterinary medicine. It is thought that immunosuppressed or immunocompromised animals are at a greater risk of developing systemic disease from exposure to and infection by this fungus. Older animals also seem to be at higher risk, as do those with poor nutritional support.
Preventing Valley Fever
No vaccine is currently available for Valley Fever. The disease cannot develop unless a dog has lived in or traveled through a region where the fungal organism is endemic. Contaminated soil in endemic areas – especially during dust or wind storms after rain – should be avoided.
Coccidioidomycosis occurs in people as well as in dogs. Owners can become infected by the fungi at the same source as their dogs. Valley Fever is not considered to be contagious. It is extremely unlikely that people can contract infection from dogs, or that people can cause infection in their pets.
Valley Fever usually can be treated, if the fungal infection is promptly and properly diagnosed. However, successful treatment can take months to years to complete.