ISOLATION OF EQUINE HERPESVIRUS 3 FROM CORNEAL AND CUTANEOUS LESIONS IN A THREE-MONTH-OLD FOAL

Equine coital exanthema (ECE) is an infectious, venereally transmitted disease of mares and stallions caused by Equid herpesvirus 3 (EHV-3). The disease is characterized by the development of superficial pustules, vesicles, erosions and ulcerations on the external genitalia (1). EHV-3 is a member of the Herpesviridae family, Alphaherpesvirinae subfamily. It is antigenically, genetically, and pathogenetically distinct from EHV-1, EHV-2, EHV-4 and EHV-5. The seroprevalence of EHV-3 in various horse populations has been estimated at 18-53% of breeding-age horses (2,3). Early work with EHV-3 found that intranasal inoculation in foals resulted in extensive ulceration and pustule formation on the nasal mucosa followed by pustules and ulcerations on the external nares (4). More recently, it was reported that EHV-3 was isolated from a naturally-occurring lesion on the nostril of a 2-month-old foal (5), demonstrating that natural horse-to-horse transmission of EHV-3 is possible in the absence of coitus. EHV-2-associated keratitis has been widely reported, with manifestations including irregular linear corneal ulcerations and multifocal punctate corneal opacities (6). In this case, molecular diagnostic testing to identify EHV-2 was not performed (on samples from either the mare or the filly) based on the characteristic EHV-3 genital lesions in the mare and recent breeding activity. To our knowledge, this is the first reported case of EHV-3-associated keratitis in a foal. It emphasizes the importance of including EHV-3 as a differential for corneal, periocular and palpebral ulcerations.

S. Shrader1, J. Koehler1, M. Barba Recreo2, A. Stewart21Department of Pathobiology and 2Department of Clinical Sciences, Auburn University, Auburn, AL

A three-month-old American Quarter horse filly presented to the Auburn University Large Animal Teaching Hospital. She was bright, alert and responsive with a normal rectal temperature, respiratory rate, and heart rate. There was bilateral blepharospasm with purulent discharge from the right eye and epiphora of the left eye. Bilaterally, the palpebrae were moderately edematous with extensive areas of depigmentation, conjunctival hyperemia and chemosis. Additionally, palpebral and periocular skin were effaced by multiple, variably-sized ulcers, vesicles, and papules. The right cornea was markedly edematous with circumferential peripheral neovascularization. There were two 5-mm diameter ulcers in the dorsal quadrant of the right cornea; both had positive retention of fluorescein. Miosis of the right pupil and the presence of severe corneal edema precluded complete examination of the intraocular structures. The left cornea had multifocal punctate ulcers with positive retention of fluorescein. The anterior uvea, lens, and posterior segment of the left eye were unremarkable. Multifocally, ulcerations and erosions were present on the cutaneous and mucosal surfaces of the lips. Due to the severity of the corneal ulcers, treatment expense and guarded prognosis, the foal was humanely euthanized and submitted for necropsy evaluation.

The foal’s dam also presented to the teaching hospital with perianal and perivulvular vesicles and ulcerations that developed one week after breeding.

CLINICAL HISTORY

DISCUSSIONFigure 1. Necropsy image showing extensive, multifocal to coalescing, variably sized (up to 2.5-cm diameter), irregularly shaped, well-demarcated erosions, ulcerations, and crusts extending circumferentially around the right eye. The cornea is pale-blue and opaque with multifocal areas of neovascularization. Slightly dorsal to the corneal center are two ill-defined, roughly 5-mm diameter, pale-blue to white ulcers (arrows).

Figure 2. Necropsy image showing ulcerations and erosions on the cutaneous and mucosal surfaces of the lips and adjacent to the incisors on the oral and labial mucosa.

1. Barrandeguy M and Thiry E. Equine coital exanthema and its potential economic implications for the equine industry. Vet J 2012;191:35–40.

2. Bagust TJ et al., Studies on equine herpesviruses. 3. The incidence in Queensland of three different equine herpesvirus infections. Aust Vet J. 1972; 48:47-53.

3. Pascoe RR and Bagust TJ. Coital exanthema in stallions. Journal of Reproduction and Fertility Supplement. 1975; 23:147-150.

4. Wilks CR and Studdert MJ. Equine herpesviruses. 6. Sequential infection of horses with types 2, 3 and 1. Aust Vet J. 1976; 52(5):1999-203.

5. Crandell RA and Davis ER. Isolation of equine coital exanthema virus (equine herpesvirus 3) from the nostril of a foal. JAVMA 1985;187(5):503-504.

6. Cutler TJ. Corneal epithelial disease. Vet Clin North Am Equine Pract 2004;20:319–43.

REFERENCES

A three-month-old American Quarter horse filly presented to the Auburn University Large Animal Teaching Hospital following one week of blepharospasm, epiphora, ocular discharge, corneal ulcers involving the right eye, and periocular and perioral erosions/ulcerations. The foal’s dam also presented to the hospital with perianal and perivulvular ulcerations. Due to the severity of the corneal ulcers, treatment expense and prognosis, the foal was euthanized and submitted for necropsy evaluation. Grossly, the right eye was surrounded by erosions, ulcerations and crusts. The right cornea was light blue and opaque with two central corneal ulcers. Similar erosions, ulcerations and crusts were observed around the left eye, on the gingival mucosa and on the cutaneous and mucosal surfaces of the lips. Histologically, the periocular erosions and ulcerations were characterized by serocellular crusts overlying degenerate or necrotic epithelial cells. Viable epithelial cells often contained 4-µm to 7-µm diameter eosinophilic to amphophilic intranuclear viral inclusions that marginated chromatin. Viral inclusions were also observed within epithelial cells adjacent to labial mucosal ulcerations. Affected sections of cornea and skin were submitted to the University of Kentucky Veterinary Diagnostic Laboratory to test for Equine Herpesvirus-3 (EHV-3), the causative agent of equine coital exanthema. Submitted sections from the foal and a vulvar swab from the mare were positive for EHV-3 via PCR. EHV-3 is endemic in most equine breeding populations; however, it is uncommonly isolated from cutaneous facial lesions in foals who have affected dams. To our knowledge, this is the first report of an EHV3-associated corneal lesion.

ABSTRACT HISTOPATHOLOGY

NECROPSY EXAMINATIONThe filly’s necropsy examination found severe, multifocal to coalescing, variably sized (up to 2.5-cm in diameter), irregularly shaped, well-delineated ulcerations, erosions, and cutaneous crusts extending circumferentially around the right eye. The right cornea was pale-blue and opaque with areas of peripheral neovascularization. Slightly dorsal to the corneal center were two ill-defined, roughly 5-mm diameter pale blue to white ulcers (Figure 1). Multifocal cutaneous erosions and ulcerations also extended from the medial canthus of the left eye to the dorsal aspect of the superior palpebra. Additionally, ulcerations and erosions were present on the cutaneous and mucosal surfaces of the lips and adjacent to the incisors on the oral labial mucosa (Figure 2).

The periocular erosions and ulcerations were characterized by multifocal, variably thick serocellular crusts overlying areas of degenerate or necrotic epithelium. Adjacent epithelial cells were frequently dysplastic or hyperplastic; individual cells often contained a single 4-µm to 7-µm diameter eosinophilic to amphophilic intranuclear viral inclusion body that resulted in chromatin margination (Figure 3). Viral inclusions were also present within intact epithelial cells associated with labial mucosal ulcerations. Ulcerated areas of the right cornea were submitted for EHV-3 PCR and virus isolation and thus were not examined histologically. The remaining portions of the right cornea were characterized by a lymphoplasmacytic and suppurative keratitis; however, viral inclusions were not observed.

PCR AND VIRUS ISOLATIONSamples collected from both the filly and mare were submitted to the University of Kentucky Veterinary Diagnostic Laboratory to test for the presence of Equine Herpesvirus 3 (EHV-3), the causative agent of equine coital exanthema. Submitted sections from the filly’s right cornea and lip were positive via PCR for EHV-3. EHV-3 was not detected via PCR from the filly’s right eyelid or left cornea. EHV-3 was also identified via virus isolation from the filly’s right cornea, right eyelid, and lip. Samples taken from the mare’s vulva were positive via PCR for EHV-3; however, EHV-3 was not detected via virus isolation.

Figure 3. Photomicrograph showing hyperplastic and dysplastic epithelial cells adjacent to an area of periocular erosion and ulceration. Individual epithelial cells often contain a single 4-µm to 7-µm diameter eosinophilic to amphophilic intranuclear viral inclusion body that marginates the chromatin (arrows). H&E. Bar = 20 µm.