INFECTED CELL-TYPES IN OVINE LUNG FOLLOWING EXPOSURE TO BOVINE RESPIRATORY SYNCYTIAL VIRUS

Sixteen adult sheep (ten females, six males obtained from a dosed floc k at National Animal Disease Center, Ames, IA) were experimentally inf ected with bovine respiratory syncytial virus strain 375 (BRSV), and l ung tissues were stained for viral antigen. Two infected sheep were eu thanatized at each of the following post-inoculation times: 12, 24, 36 , 48, 72, 96, 144, and 192 hours. Lung, nasal turbinates, trachea, rig ht cranial bronchial and mediastinal lymph nodes, liver, and spleen we re collected for histologic evaluation. An indirect immunoperoxidase t echnique was performed on routine paraffin-embedded sections of lung t issue, trachea, turbinates, and bronchial and mediastinal lymph nodes to determine the location of the BRSV antigen. For lung tissue from ea ch sheep 400 light microscopic fields at 160x magnification were exami ned for staining for BRSV antigen. Lung tissue was also collected for virus and bacterial isolation. Daily serum samples were taken for dete rmination of anti-BRSV titers. Severe respiratory disease was not prod uced in any sheep. Bovine respiratory syncytial virus was isolated fro m lung tissue collected from all sheep up through 144 hours postinocul ation At 12 hours post-inoculation (case No. 2) respiratory syncytial virus antigen was detected in bronchiolar epithelium and a mononuclear cell within an alveolar space. Lung tissue from the sheep necropsied between 24 and 144 hours post-inoculation (case Nos. 3-14) contained B RSV antigen in bronchiolar epithelium, type I pneumocytes, type II pne umocytes, alveolar macrophages, and mononuclear cells within alveolar spaces. Macrophages staining for viral antigen were rare. Bronchiolar and type I epithelial cells comprised the majority of infected cells. In a separate experiment, lung slices inoculated in vitro with either BRSV or ovine adenovirus did not stain for the respective antigens. Sl ices inoculated with parainfluenzavirus-3 did stain for that viral ant igen.