Phycomycosis of the horse caused by Basidiobolus haptosporus

A case of subcutaneous phycomycosis of a horse from which Basidiobolus haptosporu was isolated is described. Although some clinical signs were similar to the disease caused by Hyphomyces destruens, the gross and microscopic pathology were different in several respects. Main characteristics of the histopathology were the narrow eosinophilic sleeve around wide, frequently septate hyphae scattered throughout the affected tissue and found commonly at the advancing border of the lesion. A retrospective study of 63 cases of phycomycosis diagnosed at this laboratory since 1970 indicated a further 11 cases with similar histological features. The significance of this finding for the epidemiology and pathogenesis of equine dermal granulomas is discussed.