Three viruses of the bovine respiratory disease complex apply different strategies to initiate infection.

Bovine respiratory disease complex (BRDC) is the major cause of serious respiratory tract infections in calves. The disease is multifactorial, with either stress or reduced immunity allowing several pathogens to emerge. We investigated the susceptibility of bovine airway epithelial cells (BAEC) to infection by the three major viruses associated with the BRDC: bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BHV-1) and bovine parainfluenza virus type 3 (BPIV3). For this purpose, two culture systems for well-differentiated BAEC were used: the air-liquid interface (ALI) system, where filter-grown BAEC differentiate into a pseudostratified respiratory epithelium and precision-cut lung slices (PCLS) where BAEC are maintained in the original tissue organisation. Comparative infection studies demonstrated that entry and release of BPIV3 occurred specifically via the apical membrane with ciliated cells being the major target cells. By contrast, airway epithelial cells were largely resistant to infection by BHV-1. When the epithelial barrier was abolished by opening tight junctions or by injuring the cell monolayer, BHV-1 infected mainly basal cells. Respiratory epithelial cells were also refractory to infection by BRSV. However, this virus infected neither differentiated epithelial cells nor basal cells when the integrity of the epithelial barrier was destroyed. In contrast to cells of the airway epithelium, subepithelial cells were susceptible to infection by BRSV. Altogether, these results indicate that the three viruses of the same disease complex follow different strategies to interact with the airway epithelium. Possible entry mechanisms are discussed.

Infection of differentiated airway epithelial cells from caprine lungs by viruses of the bovine respiratory disease complex.

Bovine respiratory syncytial virus (BRSV), bovine parainfluenza virus type 3 (BPIV3) and bovine herpesvirus type 1 (BHV-1) are important pathogens associated with the bovine respiratory disease complex (BRDC). Non-bovine ruminants such as goats may also be infected and serve as a virus reservoir to be considered in the development of control strategies. To evaluate the susceptibility of caprine airway epithelial cells to infection by viruses of BRDC, we established a culture system for differentiated caprine epithelial cells. For this purpose, we generated precision-cut lung slices (PCLS), in which cells are retained in their original structural configuration and remain viable for more than a week. The three bovine viruses were found to preferentially infect different cell types. Ciliated epithelial cells were the major target cells of BPIV3, whereas BHV-1 preferred basal cells. Cells infected by BRSV were detected in submucosal cell layers. This spectrum of susceptible cells is the same as that reported recently for infected bovine PCLS. While infection of caprine cells by BRSV and BPIV3 was as efficient as that reported for bovine cells, infection of caprine cells by BHV-1 required a tenfold higher dose of infectious virus as compared to infection of bovine airway cells. These results support the notion that non-bovine ruminants may serve as a reservoir for viruses of BRDC and introduce a culture system to analyze virus infection of differentiated airway epithelial cells from the caprine lung.