Equid herpesvirus 5-associated dermatitis in a horse--Resembling herpes-associated erythema multiforme.

An equid herpesvirus 5 (EHV-5) infection was detected in lesioned skin from a nine-year-old Holsteiner stallion in the south of Germany. Macroscopically, the animal displayed a non-pruritic, multifocal, pustular dermatitis around both eyes, nostrils and the muzzle, which had been ongoing for one year. Histopathologically, skin lesions were characterized by orthokeratotic to parakeratotic hyperkeratosis, pustular dermatitis, epidermal hyperplasia, apoptotic keratinocytes, a lympho-plasmahistiocytic interface dermatitis with hydropic degeneration of keratinocytes, and perivascular to diffuse, lympho-histiocytic infiltrations. The stratum granulosum and the upper part of the stratum spinosum contained multiple amphophilic, intranuclear inclusion bodies. By in situ hybridization and immunohistochemistry herpesvirus DNA and protein, respectively, were detected within keratinocytes containing inclusion bodies. Sequencing of the PCR-product revealed the presence of EHV-5 DNA. This is the first description of a dermatitis associated with EHV-5 in a horse, indicating that EHV-5 should be considered as an etiology of lymphohistiocytic interface dermatitis with intranuclear inclusion bodies in horses and is similar to herpes-associated erythema multiforme in humans.