BRONCHOPNEUMONIA IN MICE CAUSED BY PASTEURELLA-HAEMOLYTICA A2 AFTER PREDISPOSITION BY OVINE BORDETELLA-PARAPERTUSSIS

Initial intranasal inoculation of four to eight-week-old Swiss White m ice with 7.5 X 10(6) colony forming units (cfu) of ovine B. parapertus sis followed 30 min, three or five days, by intranasal inoculation wit h 1.4 X 10(5) cfu of Pasteurella haemolytica A2 resulted in a more sev ere infection pattern than when either agent was administered alone. H istopathological examination showed that inoculation with B. parapertu ssis alone caused a bronchopneumonia the severity of which was dependa nt upon the infecting dose. Bacteria were recovered up to 10 days afte r inoculation. P. haemolytica alone had no apparant pathogenic effect and was cleared from the lungs within 24 h. When both agents were give n in combination the lesions were most severe when P. haemolytica was administered three days after B. parapertussis infection. These findin gs suggest that B. parapertussis predisposes mice to subsequent infect ion with P. haemolytica and that the timing of the P. haemolytica admi nistration influences the severity of the lung lesions.