Equine Herpesvirus 2-Associated Granulomatous Dermatitis in a Horse

Granulomatous dermatitis in horses has been linked to many etiologies, including various parasites, fungi, and bacteria. Idiopathic forms of granulomatous inflammation-producing diseases, some of which are localized to the skin, also have been reported in horses. Herein we describe a case of recurrent equine granulomatous skin disease characterized by intranuclear viral inclusions within macrophages and giant cells. The histologic changes were primarily noted in the deep dermis and included multifocal to coalescing areas of necrosis marked by histiocytic cell infiltration and presence of giant cells. Electron microscopic examination revealed intranuclear and intracytoplasmic viral particles consistent with herpesvirus. Sequence results of the polymerase chain reaction product were consistent with equine herpesvirus 2, adding another possible etiology to the list of differentials in cases of equine granulomatous skin disease.