Causes of Upper Respiratory Tract Infection in Dogs
The two most common causes of URT infection in dogs are bacterial and viral. These infectious pathogens are highly contagious, especially when dogs congregate in high-density areas such as pet stores, animal shelters, boarding facilities, dog parks or dog shows, and even more so when those areas are not kept clean. Immunocompromised dogs, puppies and unvaccinated dogs are at an increased risk for developing URT disease.
Bacteria and Viruses
Bordetella bronchiseptica is the most common primary bacterial pathogen causing canine URT infection (it causes infectious tracheobronchitis, commonly called “kennel cough”). The signs associated with URT infection caused by Bordetella bronchiseptica are indistinguishable from the early signs caused by secondary bacterial pathogens, including Pseudomonas, Escherichia coli, Klebsiella, Pasteurella, Streptococcus, Mycoplasma and several other bacterial species.
Viral causes of canine upper respiratory tract infection in dogs include the canine distemper virus, canine adenovirus type 1 or 2 (CAV-1 causes infectious canine hepatitis and CAV-2 is a cause of kennel cough), canine parainfluenzavirus (CPI), canine influenza virus (CIV), canine reovirus type 1, 2 or 3 and canine herpes virus. CAV-2 and the canine parainfluenzavirus can damage the respiratory epithelium so severely that affected dogs are highly likely to develop serious upper airway disease.
The canine nasal mite, Pneumonyssoides caninum, is an arthropod found in the nasal cavities and sinuses of dogs. When present, these mites cause sneezing, chronic nasal discharge (runny nose), coughing, inflammation and swelling of the nasal mucosa and epistaxis (nose bleeds), and can predispose infected dogs to secondary bacterial infections of the upper respiratory tract. They are transmitted between dogs based on direct contact with an infected animal. Fortunately, these nasal mites are uncommon in North American dogs.
Lung flukes (Paragonimus kellicotti) are trematode parasites that live within pulmonary cysts in the lungs of dogs, cats and other mammals, including people. There is no age, gender or breed predisposition to infection by lung flukes. For any mammal to become infected, it must somehow ingest part of an infected crayfish at some point in time (this is part of the life cycle of this parasite). Lung fluke infection often causes no visible clinical signs. The most common sign if any is seen is chronic coughing that does not respond to antibiotic therapy.
Most canine URT infections are preventable with proper use of vaccines and appropriate sanitation and quarantine measures. Companion dogs with strong immune systems that are supported by good nutrition, a healthy lifestyle and proper environmental hygiene can usually overcome the adverse effects of URT ailments without prolonged treatment. Because these infections are perpetuated by the shedding of pathogens in respiratory secretions, it is important to practice cleanliness and good hygiene in areas where dogs congregate in close quarters. Dogs with URT infections should be isolated from other dogs until their infection has resolved.
Uncomplicated upper respiratory tract infections usually can be successfully treated with outpatient supportive care, exercise restriction, non-steroidal anti-inflammatory drugs (NSAIDs), cough suppressants, bronchodilators and possibly antibiotics. However, some primary and secondary respiratory infections are very serious, particularly in young puppies, elderly dogs and dogs with compromised immune systems. Dogs with severe disease may need to be hospitalized. The canine distemper virus can cause severe systemic disease and frequently is fatal, especially to very young, unvaccinated dogs.