Sheep-Associated Malignant Catarrhal Fever–Like Skin Disease in a Free-Ranging Bighorn Sheep ( Ovis canadensis ), Alberta, Canada

Skin disease in sheep (Ovis aries): A retrospective report of 299 cases at a university veterinary medical teaching hospital (1986-2020)

BACKGROUND

Skin diseases in sheep are important animal health and production problems, especially in wool-producing sheep.

HYPOTHESIS/OBJECTIVES

To document the type, signalment, associations and prevalence of skin disease in a referral hospital population.

ANIMALS

Case population at a university veterinary medical teaching hospital.

MATERIALS AND METHODS

Retrospective study by searching computerised medical records of sheep examined between 1 January 1986 and 1 January 2021.

KEYWORDS

'alopecia, Arcanobacterium pyogenes, Corynebacterium, Demodex, dermatitis, Dermatophilus, dermatophyte, ectoparasite, examination, fibre damage, foot rot, fungus, interdigital necrobacillosis, itching, lice, Malassezia, melanoma, mite, pruritus, rubbing, scabies, skin, SCC, squamous cell carcinoma, Staphylococcus, Trueperella pyogenes, wool break, wool loss'.

RESULTS

Two thousand and two records, totalling 11,799 sheep, had the age, breed and sex reported. Older sheep were more likely to present with skin disease (p < 0.0001; standard deviation 36.6 ± 1.15 confidence interval). The American Merino, East Friesian, Rambouillet, Suffolk and Shetland breeds were at higher risk of developing skin disease (p < 0.0001). Males, whether rams or wethers, were more likely to present with skin disease than ewes (p = 0.0019). Owing to the lack of dermatological examination reported, the four largest flocks (a total of 7,892 sheep) were excluded from disease analysis. Of the remaining 3,907 sheep, 299 (7.6%) had skin disease recorded. The most common diagnoses made were pododermatitis, bacterial abscesses, squamous cell carcinoma and myiasis. Fifty-five of 299 sheep were presented primarily for nonskin disease.

CONCLUSIONS AND CLINICAL RELEVANCE

Clinicians should include a dermatological examination in sheep regardless of the reason for presentation.

Malignant catarrhal fever in a goat: manifestation of virus-induced erythema multiforme

Malignant catarrhal fever (MCF), caused by ovine herpesvirus 2 (OvHV2; Orthoherpesviridae, Macavirus ovinegamma2), has sheep as natural hosts. OvHV2 is an important macavirus globally that induces fatal disease in dead-end hosts. Goats, which can be infected subclinically with OvHV2, rarely develop MCF. A 28-wk-old female goat was presented with fever and multifocal crusty skin lesions. Histologic examination of a skin biopsy suggested erythema multiforme (EM), with pyoderma and dermal vasculitis. The doe was euthanized and subjected to postmortem and histologic examination. MCF was suspected and PCR assays for macaviruses were performed, followed by immunohistochemistry (IHC) for OvHV2 latency-associated nuclear antigen (oLANA), RNA in situ hybridization for Ov2.5 mRNA, and IHC to characterize infiltrating leukocytes. The main postmortem finding was severe multifocal ulcerative dermatitis with macrophage- and T cell-mediated arteritis. The latter was also detected in kidney, spleen, heart, and intestinal wall. The PCR assay detected high loads of OvHV2 in tissues. OvHV2 oLANA and Ov2.5 mRNA were expressed within the lesions in leukocytes, endothelial cells, fibroblasts, and/or keratinocytes. Our case confirms that MCF can initially manifest clinically as a skin disease in goats and as EM with confirmed viral etiology.

Granulomatous mural folliculitis in 16 domestic goats: Infection with malignant catarrhal fever viruses and colocalization with ovine herpesvirus-2 using in situ hybridization

Granulomatous mural folliculitis (GMF) is an uncommon reaction pattern occasionally observed in nonadapted ruminant hosts infected with malignant catarrhal fever viruses. This report characterizes GMF and concurrent cutaneous lesions in 16 goats with crusting dermatitis using histochemistry including hematoxylin and eosin, periodic acid-Schiff, and Grocott's methenamine silver, and immunohistochemistry for CD3, CD20, ionized calcium binding adaptor molecule 1, and cytokeratin AE1/3. Infiltrates in all 16 GMF cases consisted of macrophages and fewer T lymphocytes, and variably included eosinophils, multinucleated histiocytic giant cells, and/or neutrophils. Formalin-fixed paraffin-embedded skin and fresh skin samples from caprine GMF cases were tested using pan-herpesvirus nested conventional polymerase chain reaction (PCR) and partial sequencing, ovine herpesvirus-2 (OvHV-2) real-time PCR, and OvHV-2 colorimetric in situ hybridization (ISH). Five of 16 goats with GMF (31%) were PCR positive for malignant catarrhal fever viruses, including caprine herpesvirus 3 in 1 goat and OvHV-2 in 4 goats. Three goats also had positive intranuclear OvHV-2 hybridization signal in follicular keratinocytes, among other cell types, localized to areas of GMF. Herpesviruses were not detected in the formalin-fixed paraffin-embedded skin of 9 goats without GMF. This case series describes relatively frequent detections of malignant catarrhal fever viruses in the skin of goats with GMF, including the first report of caprine herpesvirus 3, and localizes OvHV-2 infected follicular keratinocytes within areas of GMF.

Domestic sheep and bighorn sheep carry distinct gammaherpesviruses belonging to the genus Macavirus

The genus Macavirus of the subfamily Gammaherpesvirinae comprises two genetically distinct lineages of lymphotropic viruses. One of these lineages includes viruses that can cause malignant catarrhal fever (MCF), which are known as MCF viruses (MCFV). All MCFVs are genetically and antigenically related but carried by different hosts. In this study, we report the recognition of new MCFV carried by bighorn sheep. The virus was first identified in a bighorn sheep from Banff National Park, Alberta, Canada. Analysis of a conserved region of the viral DNA polymerase gene of the virus carried by this bighorn sheep showed 85.88% nucleotide identity to the MCFV carried by domestic sheep, ovine herpesvirus 2 (OvHV-2). Further investigation of bighorn samples obtained from animals in the US and Canada showed 98.87-100% identity to the DNA polymerase sequence of the first bighorn in the study. Phylogenetic analysis indicated that the MCFV carried by bighorn sheep is closely related but distinct from OvHV-2. Epidemiological and virulence features of the newly recognized MCFV are still unknown and warrant further investigation. Considering the current nomenclature for MCFVs, we suggest a tentative designation of ovine herpesvirus-3 (OvHV-3) for this newly identified bighorn sheep MCFV.

High copy number of ovine gammaherpesvirus 2 DNA associated with malignant catarrhal fever-like syndrome in a lamb

Domestic and wild sheep are the natural reservoirs for ovine gammaherpesvirus 2 (OvHV-2), the causative agent of sheep-associated malignant catarrhal fever (SA-MCF). Virtually all adult sheep are infected with OvHV-2 under natural flock conditions, and infection is normally subclinical. MCF-like clinical signs and typical histologic lesions in sheep have been linked during case investigations at veterinary diagnostic laboratories; however, the confirmation of naturally occurring MCF in sheep is problematic. To date, the assays for detection of OvHV-2-specific antibodies or DNA are usually positive in sheep, regardless of health status, so mere detection of antibodies or the agent is of minimal diagnostic significance in this species. We document herein a naturally occurring MCF case in a 4-mo-old domestic lamb and demonstrate that the affected animal had 100-1,000 times more OvHV-2 copy numbers in tissues than in healthy adult and age-matched sheep. These results indicate that high copy numbers of viral DNA in tissues associated with characteristic lesions can be used to confirm the diagnosis of MCF in sheep.