Lesions in lambs experimentally infected with bovine respiratory syncytial virus

An experimental model was designed to characterize lesions in the lung of lambs inoculated with bovine respiratory syncytial virus (BRSV). 25 Merino lambs of both sexes, with a live weight of 17 +/- 3 Kg, received an intratracheal inoculation of 20 ml saline solution containing 1.26 x 10(6) TCID50 BRSV (strain NMK-7) per ml. Lambs were slaughtered 1, 3, 7, 11 and 15 postinoculation days (PID), and histopathological, immunohistochemical and electron microscopic studies were performed. Results reflected a series of lesions, the most noteworthy of which were bronchiolitis obliterants with destruction of the mucociliary apparatus, the presence of syncytial cells in alveoli and a progressive interstitial reaction. BRSV antigen was detected in lung samples. These changes might be expected to decrease the efficiency of respiratory tract defence mechanisms, rendering the lung parenchyma susceptible to opportunist bacterial infection.