Association of equine gammaherpesvirus-5 with facial lymphohistiocytic interface dermatitis in seven adult horses from the United States.
Authors: Peters-Kennedy Jeanine, Löhr Christiane V, Cossic Brieuc, Glaser Amy L, Duhamel Gerald E
Journal: Veterinary pathology
Summary
# Editorial Summary: EHV-5 and Facial Interface Dermatitis Equine gammaherpesvirus-5 (EHV-5) is ubiquitous in asymptomatic horses but has been implicated in pulmonary and occasional dermatological disease; this pathology study investigates whether the virus is causally linked to a previously unreported form of facial dermatitis. Researchers retrospectively examined diagnostic laboratory records from 2007–2022 across two US centres, identifying 12 cases of equine interface dermatitis and screening histological samples for viral inclusion bodies, before confirming EHV-5 presence via qPCR, in situ hybridisation, and electron microscopy. Seven horses exhibited a distinctive clinical presentation of chronic (up to several years), non-pruritic, alopecic crusted lesions predominantly on the muzzle and face, characterised histologically by CD3+ T-lymphocyte-dominated interface dermatitis with hydropic keratinocyte degeneration and herpesviral intranuclear inclusions; EHV-5 was confirmed in all seven cases but absent from five control horses and five dermatitis cases lacking inclusion bodies. Notably, one affected horse subsequently developed equine multinodular pulmonary fibrosis (EMPF), suggesting EHV-5 may target multiple epithelial tissues. Clinicians encountering chronic, non-painful facial alopecia with unusual distribution patterns should consider EHV-5 as a differential diagnosis and may benefit from tissue sampling for viral confirmation, particularly given the potential for systemic progression in some individuals.
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Practical Takeaways
- •Consider EHV-5 as a differential diagnosis in horses with chronic, non-pruritic facial dermatitis characterized by crusty lesions and hair loss, particularly on the muzzle
- •Be aware that EHV-5-associated dermatitis may represent an early or concurrent manifestation of systemic disease (EMPF), warranting thorough respiratory evaluation
- •Histopathology with qPCR or in situ hybridization is necessary to confirm EHV-5 involvement, as the virus is commonly found asymptomatically in healthy horses
Key Findings
- •Seven adult horses presented with crusted, alopecic, non-pruritic facial dermatitis (predominantly muzzle) persisting up to several years with histologic evidence of CD3+ T lymphocyte-dominated interface dermatitis
- •EHV-5 was confirmed by qPCR and/or in situ hybridization in all 7 cases, with intranuclear inclusion bodies visible in keratinocytes of upper stratum spinosum and stratum granulosum
- •One horse with EHV-5-associated dermatitis subsequently developed equine multinodular pulmonary fibrosis
- •EHV-5 was not detected in 5 control horses or in 5 horses with interface dermatitis lacking viral inclusion bodies