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Title: The pathology of malignant catarrhal fever, with an emphasis on ovine herpesvirus 2

item O'TOOLE, D - University Of Wyoming
item Li, Hong

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2013
Publication Date: 3/1/2014
Citation: O'Toole, D., Li, H. 2014. The pathology of malignant catarrhal fever, with an emphasis on ovine herpesvirus 2. Veterinary Pathology. 51(2):437-52.

Interpretive Summary: Sheep-associated malignant catarrhal fever (SA-MCF), a frequently fatal disease primarily of ruminant species, is caused by ovine herpesvirus 2 (OvHV-2), which is carried by domestic and wild sheep. SA-MCF has emerged as a significant threat to American bison due to their high disease-susceptibility and the steady increase in the bison population. This review summarizes recent progress in our understanding of sheep-associated MCF, focusing on OvHV-2 largely from the the standpoint of diagnostic pathologists.

Technical Abstract: The enigmatic pathogenesis of malignant catarrhal fever (MCF) involves dysregulated immune responses in susceptible ruminant species. Economically important outbreaks of MCF are due to two of the 10 viruses that currently comprise the malignant catarrhal fever virus group: ovine herpesvirus 2 (OvHV-2) and alcelaphine herpesvirus 1 (AlHV-1). Attempts to develop effective vaccines for this family group of viruses in the 1970s were sufficiently discouraging that they were temporarily abandoned. This review focuses on recent efforts to understand the pathogenesis of MCF, particularly the sheep-associated form of the disease, with the goal of developing rational control methods, including vaccination. The past two decades have seen several advances, including expansion of the MCF virus group, better diagnostic assays, induction of disease by a natural route (aerosol), and clearer understanding of OvHV-2 shedding patterns by domestic sheep. A consistent theme in experimental studies of using OvHV-2 in susceptible species is that there two peaks of OvHV-2 gene expression: a pre-clinical peak involving the respiratory tract, and a second in multiple organ systems that leads to clinical disease. Latent and lytic gene expression may coexist in tissues during clinical stages in symptomatic animals.