Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2007
Publication Date: 3/3/2008
Citation: Cunha, C.W., Traul, D., Taus, N.S., Oaks, L., O'Toole, D., Davitt, C.M., Li, H. 2008. Detection of ovine herpesvirus 2 major capsid gene transcripts as an indicator of virus replication in shedding sheep and clinically affected animals. Virus Research. 132(1-2):69-75.
Interpretive Summary: Ovine herpesvirus 2 causes a severe disease called malignant catarrhal fever (or MCF) in ruminants, including cattle, bison and deer. The virus is carried by sheep and causes no harm to the sheep. The inability to grow the virus in culture significantly constrains the research, particularly in understanding how the virus replicates in sheep and the mechanism of the disease in cattle or bison. In this study, we developed a molecular assay that identifies a viral genetic material found during the viral replication. Using this assay, we determined which tissues support viral replication in sheep during a virus shedding period, as well as in bison and cattle with clinical disease. The data showed that the viral replication is localized to the respiratory tract of shedding sheep, predominantly in the turbinate, while it occurs in virtually all tissues of cattle and bison with clinical disease. These findings represent an important initial step to understand the viral replication in sheep and in clinically affected animals. In addition, the study has validated the molecule assay, which is a useful tool to detect viral replication in animals.
Technical Abstract: The aim of this study was to identify tissues where Ovine herpesvirus-2 (OvHV-2) replication occurs in vivo. A reverse-transcriptase PCR targeting the OvHV-2 major capsid protein gene (ORF 25) was developed and the presence of transcripts used as an indicator of virus replication in naturally infected sheep, and cattle and bison with sheep-associated malignant catarrhal fever (SA-MCF). ORF25 transcripts were detected in 18 of 60 (30%) turbinate, trachea, and lung samples from five sheep experiencing a shedding episode; 12 of the 18 positive samples were turbinate. ORF 25 transcripts were not detected in any other tissue from the shedding sheep (n = 55). In contrast, 86 of 102 (84 %) samples from clinically affected bovine and bison tissues, including brain, kidney, intestine, and bladder, had ORF 25 transcripts. The data strongly suggest that OvHV-2 replication is localized to the respiratory tract of shedding sheep, predominantly in the turbinate, while it occurs in virtually all tissues of cattle and bison with SA-MCF. These findings represent an important initial step in understanding viral pathogenesis, and in potentially establishing a system for OvHV-2 propagation in vitro.