Abstract
The purpose of this study was to determine whether acute lesions induced in young lambs by coinfection with parainfluenza type 3 (PI-3) virus 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 intratracheally at 1–2-weeks of age. All lambs became pyretic, anorectic, hyperpneic, 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. haemolytica 4 DPI of PI-3 virus causing exacerbated signs of illness but all recovered within 2–3 days. Five lambs, killed 7 DPI of PI-3 virus, had extensive interstitial pneumonitis and three of these five lambs had multiple necrotic pulmonary foci with purulent to fibrinopurulent inflammation and hyperplasia of alveolar epithelium. None of the ten lambs that were killed 75 DPI of PI-3 virus were ill or had pulmonary lesions. Pasteurella 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 complete by 75 DPI and that coinfection with PI-3 virus and P. haemolytica, without other factors, is unimportant as a cause of chronic enzootic pneumonia of lambs.
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