Studies on the role of parainfluenzavirus type 3 and adenovirus in respiratory disease of sheep

Investigations were undertaken to isolate viruses from sheep, and to assess their role in respiratory diseases by means of epidemiological observations and experimental studies of their pathogenesis.Viruses were isolated from 0*7 per cent, of samples taken at necropsies and from 16 per cent, of sheep in 3 of 4 flocks currently experiencing outbreaks of respiratory disease, but not from 7 flocks with few or no signs of clinical illness.An adenovirus (strain 7769) was isolated from rectal swabs, but not nasal swabs, from 3 of 15 lambs during an outbreak of pneumonia in a group of 4 to 10-week-old lambs. This adenovirus differed antigenically from other ovine, bovine and human adenoviruses, and the species of erythro¬ cytes that were agglutinated by strain 7769 differed from those agglutinated by porcine, canine, equine and murine adenoviruses. It was concluded that strain 7769 was a previously unreported type of adenovirus and was designated ovine adenovirus type 4 (0A4).Although antibodies to the adenovirus group specific antigen were detected in only 6 per cent, of 661 sheep sera, neutralizing antibodies to 4 serotypes of ovine adenovirus were more common. Neutralizing antibodies to ovine adeno¬ virus types 1-4 were more prevalent in animals over 12 months of age.Following exposure of specific pathogen-free (SPF) - 2 - lambs to an aerosol of 0A4 virus, replication of this virus occurred in the respiratory and alimentary tracts and liver, and neutralizing antibodies could be detected in the serum and nasal secretions as early as 8 days after inoculation. Infection was associated with a mild clinical illness, detectable by auscultation only, and accompanied by lesions in the lungs and liver. The lesions found in the lungs of infected lambs were pulmonary oedema and peribronchiolar accumulations of mononuclear cells and in the livers were focal necrosis, lymphangitis and occlusive cholangitis.The clinical disease and pneumonic lesions observed in SPF lambs infected with both ovine adenovirus type 4 and Pasteurella haemolytica were no more severe than those in lambs infected with P.haemolytica alone.Enzootic pneumonia was induced consistently in SPF lambs inoculated with parainfluenza virus type 3 (PI3) followed by P.haemolytica 4 or 7 days later. Seventyeight per cent, of lambs developed severe respiratory disease by this method, 54 per cent, died and 95 per cent, had macroscopic lung lesions. The illness and lesions were more marked in lambs inoculated with both PI3 virus and P.haemolytica than in lambs inoculated with either agent alone and were associated with rapid multiplication of P.haemolytica within the lung