Experimental pneumonia in gnotobiotic calves produced by respiratory syncytial virus.

A bovine isolate of respiratory syncytial virus (RSV), when inoculated intranasally into eight gnotobiotic calves produced significant macroscopic lesions of the lung (2-25% consolidation) but failed to produce any clinical signs of disease. The microscopic lesions comprised proliferative and exudative bronchiolitis with accompanying alveolar collapse and infiltration by mononuclear cells of the peribronchiolar tissue and alveolar walls. Virus was recovered from the nasopharynx between days 2 and 11 after infection with peak titres between days 4 and 7. Demonstration of viral antigen by immunofluorescence in nasopharyngeal cells followed a similar detection pattern. Virus was recovered from lung or detected by immunofluorescence in the bronchiolar epithelium up to 11 days following inoculation. A serological response to RSV was demonstrated both by virus neutralization and single radial haemolysis (SRH) tests, in serum of calves from 11 days following inoculation. Specific anti-RSV IgM was detected from 9 days following infection. It is suggested that the close resemblance between the experimental disease in calves and the pathology of acute bronchiolitis in children make cattle a particularly relevant model for the human disease.