Canine infectious respiratory disease complex (CIRDC) is complex and multifactorial. Host, pathogens, and environment contribute to development of respiratory disease, which is primarily characterized by cough. In most instances, viral infection results in injury to the respiratory epithelium, which increases susceptibility to infection with bacteria, Mycoplasma spp, or other organisms that compound damage to the respiratory tract and contribute to progressive clinical signs.1
The disease has been referred to as kennel cough and infectious tracheobronchitis, but CIRDC is now preferred, as this term highlights both the involvement of multiple infectious agents and that disease susceptibility depends on host immunity and environmental factors. Moreover, although the term kennel cough may be useful in discussion with pet owners, it has become somewhat synonymous with Bordetella bronchiseptica and can cause confusion because dogs with appropriate vaccination history and robust immunity can still become infected with other CIRDC pathogens. Further, clinicians and owners should understand that antibacterial drugs are not effective when CIRDC is caused by a virus.
Although B bronchiseptica was the most commonly isolated bacterium in some previous studies,2-4 recent research has suggested numerous organisms likely play a role in CIRDC.5 Molecular techniques and virus isolation have identified mycoplasmal organisms,6 previously recognized viruses known to cause disease (eg, canine adenovirus-2, canine herpesvirus-1,7 canine parainfluenza virus,4 canine distemper virus [less frequent], canine respiratory coronavirus,8 various canine influenza viruses9), and emerging and novel viruses in which the link to clinical disease is not well-recognized (eg, canine reovirus,10 canine bocavirus, canine hepacivirus, canine pneumovirus11).
CIRDC has been documented worldwide, and no host-susceptibility–related genetic factors have been identified. Seasonal patterns of CIRDC have been observed; B bronchiseptica infections have been more commonly identified in dogs during cold months.5 Any dog can be infected with CIRDC-associated pathogens; however, young dogs and those with pre-existing airway disease (eg, bronchiectasis, airway collapse, ciliary dyskinesia) may be more susceptible due to impaired airway clearance. In addition, dogs in high-density environments12 or those that are immunologically naive or immunocompromised (endogenous or exogenous) are at increased risk and appear to develop more severe disease.13