Clinical features of blister beetle poisoning in equids: 70 cases (1983-1996).

OBJECTIVE: To document clinical signs and gross pathologic changes associated with naturally acquired cantharidiasis (blister beetle poisoning) in equids. DESIGN: Retrospective study. ANIMALS: 70 equids with laboratory-confirmed blister beetle poisoning. PROCEDURE: Medical records were reviewed to obtain history, physical examination findings, feeding practices, and diagnostic test and necropsy results. RESULTS: 32 horses and 2 donkeys died from exposure to cantharidin, whereas 36 horses survived. Diet content varied, but alfalfa hay was the common component. Onset of signs of disease was rapid. Most equids had signs of gastrointestinal tract distress. Six horses had nonspecific neurologic signs. All equids dying from cantharidiasis were in shock terminally, with duration of clinical signs ranging from 3 to 18 hours. Six horses that died had no gross lesions, whereas 14 had mild to moderate erythema of gastric, small intestinal, or colonic mucosa. Only 2 horses had gastric or duodenal ulceration, and 2 had hemorrhage of the urinary bladder mucosa. One horse had cardiac muscle necrosis. Clinicopathologic data available on 10 horses included hypocalcemia, hypomagnesemia, and azotemia. Cantharidin concentrations in urine or pooled gastric-cecal contents did not always correlate with severity of disease. CLINICAL IMPLICATIONS: Blister beetle poisoning is not universally fatal in equids. Clinical signs are related to the amount of cantharidin ingested. Every horse that survived was treated aggressively. In fatal poisonings, gross lesions may be minimal or inapparent, and diagnosis must be confirmed by chemical detection of cantharidin in urine, blood, or stomach or cecal contents.