Experimental pneumonia in mice produced by combined administration of Bordetella parapertussis and Pasteurella haemolytica isolated from sheep.

One-hundred-and-thirty-seven, 3-week-old, Swiss mice were inoculated intranasally with Bordetella parapertussis and Pasteurella haemolytica which had been isolated from naturally occurring cases of chronic non-progressive pneumonia in sheep. The combined administration produced a significantly more severe bronchopneumonia which occurred earlier, persisted for a longer period and involved a higher percentage of mice than that which was produced with B. parapertussis or P. haemolytica alone. These findings demonstrate an additive or synergic action between the two agents or their metabolic products, and provide indirect evidence that such interaction may occur in ovine chronic non-progressive pneumonia.