By Amanda Lohin, DVM
The coughing dog is a common presentation in any veterinary ER. Coughing itself can be a clinical sign of a variety of disease processes, including primary disease of the lungs/airway, heart disease, or cancer. A common cause for coughing in an otherwise healthy dog is a condition called Canine Infectious Respiratory Disease (CIRD), commonly referred to as “Kennel Cough.” This is an umbrella term for several different viruses and bacteria, most of which are highly contagious and can lead to respiratory infections in dogs.
The most common CIRD pathogens include Bordetella bronchiseptica, canine parainfluenza virus, canine adenovirus-2 and Mycoplasma cynos. Two of the LESS common causes with potentially higher morbidity is the canine influenza virus and canine distemper virus. All of these pathogens, with the exception of Mycoplasma which is a normal, but opportunistic, inhabitant of the respiratory tract in dogs, are spread via respiratory secretions of other infected dogs. They can also be spread via direct dog-to-dog contact and by contaminated objects (i.e. a human’s hands, clothing, etc). Depending on the infectious agent, the incubation period for CIRD can be anywhere from 48 hours to 10 days.
In most cases of CIRD, clinical signs are mild and can include frequent and sometimes quite a loud and alarming cough, sneezing, and yellow to green mucoid discharge from the eyes and nose. The cough can be described as a hacking cough, often ending in a terminal retch where mucus and even gastric contents can be produced, which is often mistaken for vomiting. This sometimes also prompts concern that there is something caught in the dog’s throat. On physical exam, a cough can usually be elicited upon palpation of the trachea.
Fever, lethargy, loss of appetite and labored breathing are relatively uncommon, but can occur in dogs who are more severely affected: usually puppies, unvaccinated, or immunosuppressed dogs. When these more severe clinical signs are present, pneumonia secondary to CIRD is a primary concern (also known as community acquired pneumonia). More often than not, dogs with more severe signs and pneumonia are infected with more than one CIRD antigen.
Dog with bilateral nasal discharge. Photo by Dr. Craig Datz, courtesy of VIN
In cases where Mycoplasma or Bordetella (both bacteria) are one of the causative agents they can directly colonize in the lungs and result in pneumonia. However, viral CIRD antigens can also lead to pneumonia, as the viruses often destroy the normal respiratory cells and reduce the ability of the respiratory tract to protect itself, leading to secondary bacterial infections with opportunistic pathogens (such as Staphlococcus spp., Streptococcus spp., Pasteurella spp.). Ideally, when pneumonia is present, a sample of the respiratory tract secretions should be obtained to determine which bacteria are present and which antibiotic would be most effective.
Because some of these viruses are reportable diseases (namely canine distemper virus and canine influenza virus), it is always recommended to perform testing in severely affected animals to determine the causative agent(s). Bacterial agents can be grown on culture, but PCR (polymerase chain reaction) assay is the most practical, accurate and readily available test for viral detection. This test only requires a deep nasal swab and pharyngeal (back of the throat) swab, so obtaining samples is relatively easy and painless for the pet. The presence of pneumonia is detected with thoracic radiographs (xrays), and baseline blood work is recommended to assess hydration status and the patient’s immune response (making sure they have enough white blood cells to fight the infection). In rare cases, community acquired pneumonia can be severe enough to cause sepsis or lead to respiratory fatigue and arrest.
Diagnostic and treatment recommendations will vary based on individual patient assessment. Dogs only mildly affected with minor clinical signs often do not require antibiotic treatment as the infections are self-limiting and will resolve within 7-10 days. Antibiotics should be considered if fever, lethargy, loss of appetite or mucopurulent nasal discharge is present or pneumonia is detected. Dogs with pneumonia often require hospitalization for intravenous antibiotics and possibly oxygen therapy. Antitussives (anti-cough medications) can be considered for dogs who do not have pneumonia, but are contraindicated in any animal with pneumonia.
Vaccination is the most important preventative measure in controlling and preventing CIRD and vaccines are available for most of the causative agents. Although most of these vaccinations do not produce complete immunity (with the exception of canine distemper virus), vaccinated dogs tend to have lower morbidity (clinical signs are less severe) and tend to shed less antigen in their respiratory secretions (so can be less contagious to other dogs). Because most of the CIRD antigens are highly contagious, managing the environment is also very important in reducing the spread of CIRD. Affected dogs should be isolated from other dogs for at least several days beyond the resolution of clinical signs.