Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose


Synonyms: Desert Rheumatism, San Joaquin Fever, Valley Fever


This is a fungal infection seen occasionally in horses in the arid Southwestern United States and northern Mexico. It is more common in dogs and humans. It earned the name "Valley Fever" after a large outbreak in the San Joaquin Valley, California.

Coccidioides immitus is a soil living fungus found in alkaline desert soils. Inhaled, it can cause widespread nodules in the lungs and lymph nodes. It can also cause disease in other locations. It is likely very dependent on a poorly functioning immune system for establishing disease.

Diagnosis requires blood testing for antibodies to the fungus. Chest x-ray can be helpful and show typical small nodules in the lung field.

It may be responsive to systemic antifungal medications, although reports suggest that once signs are evident, most horses die. A population of Prezwalski's horses stabled in the region was apparently very susceptible to the condition, indicating a lack of appropriate immune response to the organism.

my vet's role


The prognosis is generally poor. Treatment requires long term use of antifungal medication.

further reading & resources

Related References:

Ziemer EL, Pappagianis D, Madigan JE, et. al., Coccidioidomycosis in horses: 15 Cases (1975-1984). J Am Vet Med Assoc. 1992 Sep 15;201(6):910-6.

Terio KA, Stalis IH, Allen JL, et. al. Coccidioidomycosis in Przewalski's horses (Equus przewalskii), J Zoo Wild Med. 2003 Dec. 34(4): 339-45.

Author: Doug Thal DVM Dipl. ABVP