Ulcerative keratitis in horses with equine herpesvirus-2 and -5

Herpes keratitis (corneal inflammation) is well-known in other species but not often considered in horses. The distinctive feature of the cloudy lesions and ulceration on the cornea may help with early diagnosis. Taken from the papers discussion:

The term macrodendritic ulcerative keratitis, or macrodendrite, was selected in this manuscript as it provided the most accurate descriptor for the distinct corneal lesions observed in the reported horses. Classically, herpesvirus corneal ulcerations are morphologically grouped into punctate, dendritic, and geographic categories.18 Clinically, many herpetic corneal lesions do not conveniently fit into these simple categories, and this was true for the described horses. The dendritic corneal ulcerations were much larger than is typically observed in other host species with herpesvirus infections, but the ulcers maintained the linear, branching pattern and terminal end bulbs that are closely associated with herpetic keratitis across different species.

Note well the description of “the linear, branching pattern and terminal end bulbs that are closely associated with herpetic keratitis”. Recognizing this pattern early may give you a head start on the diagnosis of this treatable condition.
DrO

Macrodendritic ulcerative keratitis and conjunctival lymphoid hyperplasia in horses with equine herpesvirus-2 and equine herpesvirus-5 infections
Vet Ophthalmol. 2023 Dec 5. doi: 10.1111/vop.13171. Online ahead of print.
Authors
Eric C Ledbetter 1 , Timothy J Cutler 2 , Nita L Irby 1
Affiliations

1 Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
2 Palm Beach Veterinary Specialists, West Palm Beach, Florida, USA.

PMID: 38053223
DOI: 10.1111/vop.13171

Abstract

Objective: The aim of this study was to describe the clinical, confocal microscopic, histologic, and virologic features of horses with macrodendritic ulcerative keratitis and conjunctival lymphoid hyperplasia associated with equine herpesvirus-2 and equine herpesvirus-5 infection.

Animal studied: Four foals with bilateral ocular disease.

Procedures: Complete ophthalmic examination was performed for each horse, and corneal samples were collected for cytology and microbiologic evaluation, including virus isolation and molecular diagnostics for the equine herpesviruses. In vivo confocal microscopy examination of the cornea was performed in two horses. Conjunctival biopsies for histopathology were collected from two horses with nodular conjunctival thickening.

Results: Each horse had bilateral, large, superficial dendritic corneal ulcerations that covered extensive regions of the corneal surface. Corneal in vivo confocal microscopy examination in two horses detected inflammatory cells and populations of morphologically abnormal corneal epithelial cells adjacent to the ulcerations. The abnormal epithelial cells included round, relatively small, hyperreflective cells intermixed with elongated, enlarged, hyperreflective cells. Equine herpesvirus-2 was isolated from corneal samples of 2 horses and detected by PCR assay in the other two horses. Equine herpesvirus-5 was also detected by PCR assay in three of the horses. Conjunctival histopathology identified predominantly lymphocytic infiltrates. The macrodendrites and conjunctival masses resolved with topical antiviral therapy (cidofovir or idoxuridine) in all horses and did not recur.

Conclusions and clinical relevance: The equine gammaherpesviruses may be associated with the development of macrodendritic ulcerative keratitis and conjunctival lymphocytic masses in foals. In vivo confocal microscopy of horses with macrodendrites revealed similar findings to other host species with herpetic dendritic keratitis.

Keywords: conjunctival lymphoid hyperplasia; cornea; dendritic ulcerative keratitis; gammaherpesvirus; in vivo confocal microscopy; macrodendrite.

© 2023 The Authors. Veterinary Ophthalmology published by Wiley Periodicals LLC on behalf of American College of Veterinary Ophthalmologists.