Coccidioidomycosis in horses: 15 cases (1975-1984)

Fifteen confirmed cases of equine coccidioidomycosis that originated in California and Arizona were studied retrospectively. Age, breed, and sex varied among affected horses. The most common historical problems were chronic weight loss (53% of cases) and persistent cough (33% of cases). The most frequent physical examination abnormalities were related to the respiratory tract (60% of cases). In 27% of cases, horses had signs of musculoskeletal pain. Horses consistently had hyperproteinemia, hyperfibrinogenemia, leukocytosis, and neutrophilia. An antemortem etiologic diagnosis was made for 11 (73%) horses, all of which had positive serologic tests for coccidioidomycosis. Of the seropositive horses, 5 (46%) also had positive cultures for Coccidioides immitis. One horse died naturally. The other 14 were euthanatized. Prolonged treatment with specific antifungal agents was attempted in 4 horses without apparent benefit. Postmortem abnormalities included pulmonary parenchymal lesions (64% of cases), thoracic lymphadenopathy (57% of cases), hepatic parenchymal involvement (43% of cases), and osteomyelitis (29% of cases). The lesions were granulomatous or pyogranulomatous and C immitis was observed microscopically in 83% of cases.