Bronchopneumonia in mice caused by Pasteurella haemolytica A2 after predisposition by ovine Bordetella parapertussis

Abstract Initial intranasal inoculation of four to eight-week-old Swiss White mice with 7.5 × 10 6 colony forming units (cfu) of ovine B. parapertussis followed 30 min, three or five days, by intranasal inoculation with 1.4 × 10 5 cfu of Pasteurella haemolytica A2 resulted in a more severe infection pattern than when either agent was administered alone. Histopathological examination showed that inoculation with B. parapertussis alone caused a bronchopneumonia the severity of which was dependant upon the infecting dose. Bacteria were recovered up to 10 days after inoculation. P. haemolytica alone had no apparant pathogenic effect and was cleared from the lungs within 24 h. When both agents were given in combination the lesions were most severe when P. haemolytica was administered three days after B. parapertussis infection. These findings suggest that B. parapertussis predisposes mice to subsequent infection with P. haemolytica and that the timing of the P. haemolytica administration influences the severity of the lung lesions.