Pathology of Blister Beetle (Epicauta) Poisoning in Horses

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Abstract
Case records of 21 horses that had acute illness after eating baled alfalfa hay containing dead striped blister beetles were reviewed. Tissue sections from 14 of the horses were examined; sections from two normal horses and several others with unrelated diseases were used for comparison. Clinical illness was characterized by abdominal pain, fever, depression, frequent urination, shock and, occasionally, synchronous diaphragmatic flutter. Laboratory findings were hemoconcentration, neutrophilic leukocytosis, hypocalcemia, hematuria and low urine specific gravity. Major morphologic changes were sloughing of the stratified squamous epithelium of the stomach, hemorrhage and ulceration in the urinary bladder, enterocolitis and myocardial necrosis. Five horses with experimental poisoning had lesions and clinical signs similar to those of the natural disease. Acute disturbance of both the gastrointestinal and urinary tracts, and the stomach and bladder lesions, were regarded as sufficiently suggestive of blister beetle poisoning to be useful in differential diagnosis, but no pathognomonic lesions were found. Therefore, striped blister beetles should be sought in hay fed to affected horses if blister beetle poisoning is suspected.