CHRONIC EFFECTS OF COINFECTION IN LAMBS WITH PARAINFLUENZA-3 VIRUS AND PASTEURELLA-HAEMOLYTICA

The purpose of this study was to determine whether acute lesions induc ed in young lambs by coinfection with parainfluenza type 3 (PI-3) viru s and Pasteurella haemolytica, would persist until slaughter age (5-6 months) and resemble those of chronic enzootic pneumonia. To do this, 16 colostrum-deprived lambs were sequentially inoculated intratracheal ly at 1-2-weeks of age. All lambs became pyretic, anorectic, hyperpnei c, and lethargic 1-2-days post-inoculation (DPI) of PI-3 virus and one died 3 DPI of the virus. The remaining lambs were given P. haemolytic a 4 DPI of PI-3 virus causing exacerbated signs of illness but all rec overed within 2-3 days. Five lambs, killed 7 DPI of PI-3 virus, had ex tensive interstitial pneumonitis and three of these five lambs had mul tiple necrotic pulmonary foci with purulent to fibrinopurulent inflamm ation and hyperplasia of alveolar epithelium. None of the ten lambs th at were killed 75 DPI of PI-3 virus were ill or had pulmonary lesions. haemolytica was isolated from the lungs of two lambs killed 7 DPI of PI-3 virus and from one lamb killed 75 DPI of PI-3 virus but no virus was isolated. Control lambs did not have signs or lesions of disease. We concluded that resolution of acute lesions in the lungs was complet e by 75 DPI and that coinfection with PI-3 virus and P. haemolytica, w ithout other factors, is unimportant as a cause of chronic enzootic pn eumonia of lambs.