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

The research paper reports the first known case of a horse with dermatitis linked to equid herpesvirus 5 (EHV-5), showing the virus may cause skin conditions like erythema multiforme commonly seen in people.

Disease Description and Manifestation

• The study revolves around a nine-year-old Holsteiner stallion that had been battling a non-itchy, pustular dermatitis located around its eyes, nostrils, and muzzle for a year.
• The horse’s skin condition manifested as orthokeratotic to parakeratotic hyperkeratosis, along with pustular dermatitis and epidermal hyperplasia. Other symptoms included apoptotic keratinocytes (programmed cell death in skin cells), lympho-plasmahistiocytic interface dermatitis with swelling and breakage of keratinocytes, and perivascular to diffuse, lympho-histiocytic infiltrations.

Investigation and Findings

• Upon closer examination, scientists observed multiple amphophilic (having an affinity for both acidic and basic dyes), intranuclear inclusion bodies in the stratum granulosum and the upper area of the stratum spinosum.
• Scientists used in situ hybridization (a technique for visualizing and determining the spatial arrangement of genetic material in cells) and immunohistochemistry (a method to visualize proteins in cells of a tissue) to discern the presence of herpesvirus DNA and proteins within the keratinocytes containing these inclusion bodies.
• Further DNA sequencing of the PCR (Polymerase Chain Reaction) product pointed to the presence of EHV-5 DNA.

Conclusions and Implications

• This study provides the first documented case of a dermatitis in horses associated with EHV-5, inferring that this virus could be a cause of skin conditions in horses similiar to herpes-associated erythema multiforme in humans.
• Such findings stress that EHV-5 needs to be considered as a potential cause of lymphohistiocytic interface dermatitis in horses, particularly if intranuclear inclusion bodies are detected.
• The discovery of EHV-5’s potential role in dermatitis may help in developing better understanding and potentially innovative treatments for this skin condition in horses.