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

Authors: PHILLIPS, IDA - Oregon State University; Cunha, Cristina; GALBRAITH, DUSTIN - Upper Valley Veterinary Clinic; Highland, Margaret; BILDFELL, ROABERT - Oregon State University; Li, Hong

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2017
Publication Date: 4/6/2018
Citation: Phillips, I.L., Cunha, C.W., Galbraith, D., Highland, M.A., Bildfell, R.J., Li, H. 2018. High copy number of ovine gammaherpesvirus 2 DNA associated with malignant catarrhal fever-like syndrome in a lamb. Journal of Veterinary Diagnostic Investigation. https://doi.org/10.1177/1040638718766976.
DOI: https://doi.org/10.1177/1040638718766976

Interpretive Summary: Sheep-associated malignant catarrhal fever (SA-MCF) is caused by ovine herpesvirus-2 (OvHV-2), a virus carried usually asymptomatically by sheep. When OvHV-2 is transmitted to disease susceptible animals, such as cattle or bison, SA-MCF may occur and is often fatal. In this report we describe a clinical case of OvHV-2-induced MCF in a domestic lamb and indicate that detection of high levels of OvHV-2 DNA in tissues of affected sheep can be used, along with clinical and pathological manifestations, to confirm the diagnosis. The simple detection of viral DNA in tissues or blood in combination with epidemiological, clinical, and pathological data is enough to confirm the diagnosis of MCF in clinically susceptible species; however, because virtually all sheep are infected with OvHV-2, detection of the virus is meaningless for diagnosis of MCF in sheep. In this study, the tissue levels of OvHV-2 DNA in the clinically affected lamb and in three different groups of sheep, which were infected with the virus but clinically normal, were compared. It was observed that the clinical animal have significantly higher levels of viral DNA in the tissues than the other groups. This suggests that quantification of viral DNA in tissues can be used as a marker and offers a helpful tool for diagnosis of SA-MCF in sheep.

Technical Abstract: 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 domestic sheep are infected with OvHV-2 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 SA-MCF in sheep is very difficult. The current diagnostic 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. In this report, we document a naturally occurring SA-MCF case in a 4-month-old domestic lamb and demonstrate that the affected animal had significantly higher levels of OvHV-2 DNA in tissues than clinically normal OvHV-2 infected sheep. These results indicate that high levels of viral DNA associated with characteristic lesions can be used to confirm the diagnosis of MCF in sheep.