CORYNEBACTERIUM-PSEUDOTUBERCULOSIS INFECTION IN HORSES - 538 CASES (1982-1993)

Objective-To describe clinical manifestations of Corynebacterium pseud otuberculosis infection in horses and to evaluate diagnostic methods f or identification of this disease. Design-Retrospective case series. A nimals-538 horses with a diagnosis of C pseudotuberculosis infection. Results-Median age of horses with external abscesses was similar to th at in horses with internal abscesses. Breed and sex did not appear to be associated with infection. Cases were detected during all 12 months ; however, the disease was most common in the fail and early winter, w ith the highest incidence in September, October, and November in every year. Most horses (492/538, 91.4%) had a single episode of infection, without recurrence in subsequent years. Of 538 horses, 308 had pector al abscesses, although infection was documented in many other anatomic locations. Forty-two horses had internal abscesses involving the abdo men or thoracic cavity. Corynebacterium pseudotuberculosis infection w as readily identified by bacterial culture of aspirate samples from ab scesses. The synergistic hemolysis inhibition test was useful for diag nosis of internal abscesses; however, it was unreliable for the diagno sis of external abscesses. Horses with external abscesses responded we ll to conventional treatment, in contrast to those with internal absce sses. The overall case fatality was low (3.9%), and was considerably l ower for horses with external abscesses (0.8%) than for horses with in ternal abscesses (40.5%). Clinical Implications-Serology (synergistic hemolysis inhibition titers greater than or equal to 512) is useful fo r diagnosis of internal abscesses, but not reliable for diagnosis in h orses with exernal abscesses. Prognosis for horses with internal absce sses is considerably poorer than for those with external abscesses.