Coccidioidomycosis in 26 horses in California, USA: case series and review of the literature

Abstract

Coccidioidomycosis is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. We searched the records of the California Animal Health and Food Safety Laboratory from 1990 through 2020 for cases of coccidioidomycosis in horses. The selection criteria for these cases were: 1) live-born horses submitted for autopsy, and 2) a diagnosis of coccidioidomycosis was established, regardless of cause of death. During that time, 19,054 horses were received, and 26 cases (0.14%) of coccidioidomycosis were diagnosed in horses, of which 19 (73%) cases had pneumonia and/or pleuritis with or without lesions in other organs, and 7 (27%) cases had lesions only in organs other than the lungs (nasal mucosa, spleen, thoracic lymph nodes, heart, pericardial sac, liver, kidney, mediastinum, and/or mesentery). Pneumonia was diagnosed as the cause of death in 1,838 (9.64%) of the horses received; Coccidioides spp. was the cause of pneumonia in 19 (1.0%) of these animals. Horses have been reported to have low susceptibility to coccidioidomycosis, and the severity and chronicity of the disease can be variable. Lesions in our cases consisted of multifocal-to-coalescing pyogranulomas with intralesional fungal spherules. Coccidioidomycosis must be considered a differential diagnosis in cases of persistent cough, chronic weight loss, fever, and cases with a travel history to, or living in, a region considered endemic for coccidioidomycosis. Coccidioides spp. infection should also be considered when pyogranulomatous inflammation is found within lung, spleen, nasal mucosa, and lymph nodes of horses.

Keywords: coccidioidomycosis; horses; pneumonia; review.

Figures 1, 2.

Coccidioidomycotic lesions in horses. Figure 1. The epicardium is covered by tan, round, firm nodules that tend to coalesce. Similar nodules also cover the surrounding pleura. Figure 2. The pulmonary parenchyma has 0.2–1-cm, pale, firm nodules throughout all lobes. Inset: higher magnification of the pale pleural nodules.

Figures 3–6.

Microscopic pulmonary lesions from horses with coccidioidomycosis. Figure 3. Multifocal areas of consolidation. H&E. Figure 4. The pulmonary parenchyma is effaced by pyogranulomatous inflammation, including abundant macrophages, lymphocytes, plasma cells, neutrophils, and multinucleate giant cells. Figure 5. Langhans giant cells with intracytoplasmic round, 20–150-µm fungal spherules, with endospores. H&E. Figure 6. Diff-Quick–stained lung impression smear with degenerate inflammatory cells and Coccidioides spp. spherules.