Systemic vasculitis and lower urinary tract obstruction in a lamb caused by ovine herpesvirus-2
Emily Brouwer
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2024;28(2):11.
An 8-week-old polled Dorset ram lamb presented to the referring veterinarian for a six-day history of stranguria and dribbling urine. During the physical examination, the veterinarian exteriorized the penis and was unable to identify any obstructions in the vermiform appendage, but noted that the prepuce contained a thick fibrin cast. During the physical examination, the veterinarian observed that the animal was also having trouble breathing, and there were thick plaques of white exudate on the roof of the mouth. The veterinarian suspected urolithiasis and pneumonia, and treated the lamb with muscle relaxants, meloxicam, florfenicol, and penicillin. The lamb died two days later and was submitted to the Animal Health Laboratory for postmortem examination.
On gross examination, the hard palate, buccal gingiva, edges of the tongue, and oropharynx were extensively coated in thick mats of yellow-tan friable exudate that was loosely adhered to underlying erosions and deep mucosal ulcers (Fig. 1). These ulcers, lined by fibrinous exudate, extended the length of the esophageal mucosa to the level of the rumen. The preputial orifice and an approximately one-centimeter band of surrounding skin was bright red, alopecic and ulcerated.
Figure 1. Mucosal ulcers covered by plaques of fibrin in the oral cavity.
Dissection of the urinary tract revealed mild dilation of the renal pelvis (hydronephrosis) with bilateral ureteral dilation (hydroureter), but the urinary bladder was empty. The mucosa of the urinary bladder was mottled pink and red with a dull surface. No obstruction was identified in the urethra, but the preputial mucosa was dark red, and the penis was adhered to the internal aspect of the prepuce by thick mats of fibrin. No vermiform appendage was identified.
The presence of hydronephrosis and hydroureter was compatible with the clinical diagnosis of lower urinary tract obstruction, and it was determined at postmortem examination that this obstruction was due to extrinsic blockage of the urethra due to extensive preputial inflammation. The process of exteriorizing the penis during physical examination likely removed the urethral blockage and allowed for micturition prior to submission.
Histopathologic examination identified widespread lymphocytic and neutrophilic vasculitis in various tissues, including the oral and esophageal mucosa, penis, prepuce, and heart. These areas of vasculitis were often associated with tissue necrosis, mucosal ulceration, and fibrinosuppurative inflammation. These histologic findings are compatible with the syndrome of systemic vasculitis caused by ovine herpesvirus-2, and subsequent PCR testing of the oral and esophageal mucosa was positive for OvHV-2 with cycle thresholds of 22.88 and 25.01, respectively.
Due to extensive oral ulceration, viral vesicular diseases, particularly Foot-and-Mouth disease (FMD), were considered. No coronary band lesions were identified, and thus a foreign animal disease was considered unlikely. Confirmatory negative testing for FMDV was performed as a precaution.
Ovine herpesvirus-2 is one of the ruminant gammaherpesviruses associated with Malignant Catarrhal Fever (MCF) in cattle and other ungulates. Sporadic cases of systemic vasculitis with clinical signs and lesions similar to MCF have been reported in Ontario sheep, and may present as excessive salivation, anorexia, and oculonasal discharge. Since sheep are the host-adapted species for this virus, infection is typically widespread and asymptomatic. The diagnosis is made when there are characteristic histologic lesions in conjunction with positive OvHV-2 PCR results. In situ hybridization has previously been performed on affected animals in Ontario and has demonstrated intralesional virus antigen in PCR-positive animals.
Lower urinary tract obstruction appears to be a novel clinical sign of this syndrome. AHL
References
1. Brooks A, et al. Systemic vasculitis in a sheep associated with ovine herpesvirus-2. AHL Newsletter 2021;25(3):6.
2. Pesavento PA, et al. Systemic necrotizing vasculitis in sheep is associated with ovine herpesvirus 2. Vet Pathol 2019;56:87-92.
3. Shapiro J, Binnington B. Be on the look-out for an unusual mucosal disease in slobbering sheep. Ceptor 2009;17:4.