Corynebacterium pseudotuberculosis Infection in the Horse: Study of 117 Clinical Cases and Consideration of Etiopathogenesis

Abstract

SUMMARY In a study of 117 cases of abscessation caused by Corynebacterium pseudotuberculosis in horses, a seasonal pattern of occurrence was found. Over a 6-year period, the peak incidence was in October and November. There was a marked variation in annual incidence, and the geographic distribution of cases did not always reflect that of the general equine population. The highest annual incidences followed winters of above average rainfall. It was believed that such winters resulted in optimal breeding conditions for insects in the subsequent summer and autumn and that increased insect populations may have resulted in increased annual incidence of the disease. Although 50% of cases typically involved the pectoral region or ventral abdominal wall, the large number of atypical sites and the diversity of clinical signs often made diagnosis difficult. Some of the more consistent signs associated with developing abscesses were superficial or deep swellings, ventral pitting edema, ventral midline dermatitis, lameness, depression, and fever. Hot packing to facilitate rupture was the preferred treatment, however surgical lancing was necessary to attain resolution in 22 cases of deep or encapsulated abscesses. Untoward sequelae (55 cases) consisted of prolonged or chronic suppurative discharge, multiple abscessation, internal abscesses, and abortion. Untoward sequelae consistently developed in cases of marked or prolonged fever and in cases of abscessation in other than the typical pectoral or ventral abdominal wall regions.