Role of canine parainfluenza virus and Bordetella bronchiseptica in kennel cough.

The effect of Bordetella bronchiseptica upper airway colonization on the clinical, radiographic, serologic, pathologic, and pulmonary function changes caused by canine parainfluenza-2 virus (CPIV-2) infection was studied in 24 purebred Beagle pups (10.5 +/- 1.4 weeks old). Eight control dogs (group I) were not colonized or inoculated with CPIV-2. Of the 12 noncolonized dogs inoculated with CPIV-2 (group II), 9 developed antibody titers to CPIV-2 and 10 had clinical signs of infectious canine tracheobronchitis (kennel cough). Group I and group II dogs did not differ in radiographic findings or pulmonary function. Four group II dogs necropsied 1 to 5 days after clinical signs developed had laryngotracheobronchitis and bronchiolar inflammation not present at necropsy on 2 group I dogs. Four dogs had B bronchiseptica upper airway colonization and were inoculated with CPIV-2 (group III). All 4 group III dogs developed positive antibody titers, had clinical signs of kennel cough, and had radiographic changes. Pulmonary dynamic compliance was lower in group III than in group I or group II animals. Respiratory rate and tidal volume did not differ among the 3 groups. The 1 group III dog that was necropsied had changes similar to group II dogs with the addition of lobar bronchopneumonia. The present study indicates that asymptomatic B bronchiseptica colonization may effect the clinical, radiographic, and pulmonary function changes produced by CPIV-2 respiratory tract infections.