Integration of bovine herpesvirus 4 genome into cultured persistently infected host cell genome

Bovine herpesvirus 4 (BoHV-4), a member of the Gammaherpesvirinae subfamily, was first isolated in Europe from respiratory and ocular diseases by Bartha and colleagues [1] and later in the United States by Mohanty and colleagues [2]. BoHV-4 has been isolated from a variety of samples and cells from healthy cattle and from cattle with abortion, metritis, pneumonia, diarrhea, respiratory infection, and mammary pustular dermatitis [3]. However, only a few investigators have successfully produced experimental disease. Although no clear direct disease associations have been demonstrated, abundant evidence consistent with a secondary role for persistent infection by BoHV-4 in bovine post-partum metritis has accumulated [4]. Like other herpesviruses, BoHV-4 establishes persistent infections in its natural host [5,6] and in an experimental host, the rabbit [7]. Although BoHV-4 has been demonstrated in many tissues, accumulated evidence suggests that the main site of persistence in both natural and experimental hosts is cells of the monocyte/macrophage lineage [8]. Based on this and other evidence, a pathogenetic model of persistent BoHV-4 infection along with bacterial co-infection has been postulated. Bacterially induced metritis in cattle persistently infected with BoHV-4 could possibly be exacerbated or become chronic following the recruitment of macrophages persistently infected with BoHV-4 from the bloodstream to the site of inflammation [9,10]. This model could explain the fact that BoHV-4 can also be isolated from healthy animals, where, in the absence of inflammation, the pathogenic potential of BoHV-4 is ameliorated. Therefore, persistent infection represents a prerequisite for BoHV-4 potential pathogenicity. However little information is available about BoHV-4 persistent infection. We previously generated in vitro models of BoHV-4 persistent infection in a human rhabdomyosarcoma cell line, RD-4 [11], and a bovine macrophage cell line, BOMAC [12]. RD-4 cells and BO