Identification of peripheral blood mononuclear cells targeted by Ovine herpesvirus-2 in sheep.

Sheep-associated malignant catarrhal fever (MCF), caused by Ovine herpesvirus 2 (OvHV-2), is usually a fatal disease of various ruminants and swine. In contrast, natural OvHV-2 infection in sheep, which are the main OvHV-2 reservoir, proceeds without any clinical symptoms. Since the range of targeted cells may be important for pathogenesis, we wanted to analyze the natural range of peripheral mononuclear blood cells (PBMC) targeted by OvHV-2. To this end, OvHV-2-free sheep were exposed to natural infection and blood samples were taken at intervals. Four different PBMC subpopulations were purified by fluorescence activated cell sorting (FACS) before being subjected to analysis for OvHV-2-DNA. After an incubation period of between 11 and 12 weeks, all exposed sheep became positive for OvHV-2. In most sheep, a first peak of OvHV-2-DNA was identified in the CD2 and CD4 double positive subpopulation. However, with time, the highest load of OvHV-2-DNA shifted to the CD2-positive and CD4-negative T-cells. Furthermore, low amounts of OvHV-2-DNA were occasionally detected also in the fractions that represented either CD14-positive monocytes or triple negative cells (CD2(-)/CD4(-)/CD14(-)). We conclude from these experiments that OvHV-2 has a similar host cellular range in sheep and cattle, respectively. Our results may be relevant in the context of comparative analysis of OvHV-2 pathogenesis in animal species that are susceptible to MCF.