How Valley Fever is Diagnosed
Valley Fever should be suspected in any dog that lives in or travels through endemic areas and develops chronic upper and/or lower respiratory signs, together with enlarged lymph nodes. Veterinarians presented with such a patient will of course perform a thorough physical examination of the dog and take a complete history from the owner. They also may perform a complete blood count and serum biochemistry panel on a blood sample, the results of which can suggest Valley Fever. A urinalysis will not help this diagnosis. Thoracic radiographs (chest X-rays) often are abnormal in dogs with coccidioidomycosis. Radiographs of the long limb bones of dogs with lameness caused by Valley Fever may be abnormal, as well.
A definitive diagnosis of Valley Fever can only be made by identifying the organism, or antibodies to the organism, in fluid, tissue or serum samples. Agar gel immunodiffusion (AGID) assays are widely used by commercial diagnostic laboratories to detect antibodies to Coccidioides immitis in blood samples taken from dogs showing signs of respiratory or systemic illness.
Coccidioides immitis can also be cultured (grown) from tissue samples taken by biopsy. However, because this fungus is so dangerously infective, only specialized laboratories that are fully equipped to handle such organisms should perform these cultures.
Diagnosis of Valley Fever is complicated by the fact that most laboratories regard the fungus as too dangerous to culture, because of the significant risk of human infection.