In situ hybridization detection of bovine respiratory syncytial virus in the lung of experimentally infected lambs

We studied the distribution of bovine respiratory syncytial virus (BRSV) RN A in lungs of experimentally inoculated lambs by in situ hybridization at d ifferent times postinoculation. The probe used for in situ hybridization wa s prepared by reverse transcription of BRSV RNA, followed by polymerase cha in reaction (PCR) amplification of the cDNA. Twenty-five Merino lambs of bo th sexes with a live weight of 17 +/- 3 kg received an intratracheal inocul ation of 20 mi saline solution containing 1.26 x 10(6) TCID50 BRSV (strain NMK7)/ml. Lambs were slaughtered 1, 3, 7, 11, and 15 days postinoculation ( PID). Bronchial and bronchiolar epithelial cells were positive for BRSV nuc leic acid by ISH at 1, 3, 7, and 11 PID. However, alveolar epithelial cells contained positive cells at 1, 3, and 7 PID. Cells containing viral RNA we re detected from 1 to 11 PID in exudate within bronchial and bronchiolar lu mina and from 3 to 7 PID in alveolar exudates. Positive hybridization signa ls were identified in interstitial mononuclear cells and in bronchi-associa ted lymphoid tissue from 3 to 11 PID. Mononuclear cells were located in per ibronchiolar tissue and interalveolar septa. The highest signal intensity i n positive cells was observed at 3 and 7 PID, coinciding with the most impo rtant histopathological findings.