Abstract
Sixteen adult sheep (ten females, six males obtained from a closed flock at National Animal Disease Center, Ames, IA) were experimentally infected with bovine respiratory syncytial virus strain 375 (BRSV), and lung tissues were stained for viral antigen. Two infected sheep were euthanatized at each of the following post-inoculation times: 12, 24, 36, 48, 72, 96, 144, and 192 hours. Lung, nasal turbinates, trachea, right cranial bronchial and mediastinal lymph nodes, liver, and spleen were collected for histologic evaluation. An indirect immunoperoxidase technique was performed on routine paraffin-embedded sections of lung tissue, trachea, turbinates, and bronchial and mediastinal lymph nodes to determine the location of the BRSV antigen. For lung tissue from each sheep 400 light microscopic fields at 160x magnification were examined for staining for BRSV antigen. Lung tissue was also collected for virus and bacterial isolation. Daily serum samples were taken for determination of anti-BRSV titers. Severe respiratory disease was not produced in any sheep. Bovine respiratory syncytial virus was isolated from lung tissue collected from all sheep up through 144 hours postinoculation. 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 postinoculattion (case Nos. 3–14) contained BRSV antigen in bronchiolar epithelium, type I pneumocytes, type II pneumocytes. 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. Slices inoculated with parainfluenzavirus-3 did stain for that viral antigen.