In situ hybridization for localization of ovine herpesvirus 2, the agent of sheep-associated malignant catarrhal fever, in formalin-fixed tissues

Authors: PESAVENTO, PATRICIA - University Of California, Davis; Cunha, Cristina; Li, Hong; JACKSON, KENNETH - University Of California, Davis; O'TOOLE, DONAL - University Of Wyoming

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2018
Publication Date: 9/16/2018
Citation: Pesavento, P., Cunha, C.W., Li, H., Jackson, K., O'Toole, D. 2018. In situ hybridization for localization of ovine herpesvirus 2, the agent of sheep-associated malignant catarrhal fever, in formalin-fixed tissues. Veterinary Pathology. 56(1):78-86. https://doi.org/10.1177/0300985818798085.
DOI: https://doi.org/10.1177/0300985818798085

Interpretive Summary: Malignant catarrhal fever (MCF) is a severe and usually fatal disease of ungulates, caused by one of a group of herpesviruses. Ovine herpesvirus 2 (OvHV-2), transmitted by sheep, is one of the most prevalent of these viruses and the cause of majority of MCF cases worldwide. There is currently no vaccine or treatment for the disease, mostly due to difficulties in locate infected cells in diseases animals. However, to develop effective strategies to control MCF it is critical that we understand how disease occurs following virus infection. In this study an in situ hybridization (ISH) approach to detect OvHV-2 DNA in infected cells was developed. The assay was specific for OvHV-2 and allowed its detection inside cells in tissues of a variety of species naturally or experimentally infected with the virus. Using ISH, it was found that the distribution of OvHV-2 in tissues correlates well with the severity of lesions and with viral loads. The ISH is a valuable tool to study MCF, especially in chronicling the natural progression of OvHV-2 infection in time-course experiments and in addressing specific aspects of the disease development.

Technical Abstract: A constraint on understanding the pathogenesis of the malignant catarrhal fever (MCF) syndrome is the limited number of tools to locate infected cells. Detectable virus, visualized either by immunohistochemistry (IHC) or in situ hybridization (ISH), has been modest in fixed or frozen tissues. This complicates our understanding of the widespread lymphoid proliferation, epithelial necrosis/apoptosis and arteritis-phlebitis which characterize MCF. Using a sensitive probe-based in situ hybridization approach, we demonstrate viral nucleic acid of ovine herpesvirus 2 (OvHV-2) in the nuclei of lymphoid cells in naturally infected species (American bison; domestic cattle and sheep) and in several species following experimental infection (American bison, rabbits, and pigs). The distribution of OvHV-2 infected cells in tissue correlate well with the severity of lymphoproliferation and inflammation, and with quantitative PCR-estimated viral loads. In situ hybridization will be of value in chronicling the natural progression of OvHV-2 infection in time-course studies following experimental infection, and in addressing specific aspects of the pathogenesis of MCF.