Canine Coughs by Dr. Gawen Thompson

At any given time during the ownership of a dog, you may encounter an episode of coughing. Often this can be viral infection known as infectious tracheobronchitis or “kennel cough”, but there are some other possibilities and it always helps owners to be aware of some of the subtle differences.

The origin of a cough is the key to its cause. The airway is referred to as the respiratory tract and it is divided into two parts which are very different both in terms of structure and the problems that affect them. The upper respiratory tract consists of the mouth and nasal passages, pharynx (throat) and the portion of the trachea (wind-pipe) that is in the neck. The upper airway creates more resistance at the time of inhalation, and as a result a wheeze on inspiration will be originating there. The lower respiratory tract consists of the lungs, small airways (bronchi) and the thoracic trachea – basically, all the components in the chest. There is more resistance here when exhaling and noises in the chest on exhalation point to a problem there.

A cough is a sign of irritation of the airway regardless of the location. It can be very difficult to figure out the source of the cough, so a physical examination and auscultation (listening to the chest with a stethoscope) of the airways by a veterinarian is always appropriate. Diagnostics and treatments can then be recommended depending on history and findings.

Diseases:

For this discussion we will consider four main causes for coughing (be aware there are more): 1. Obstruction/foreign body; 2. Cardiac disease; 3. Infectious tracheobronchitis (Kennel cough) and 4. Allergic airway disease

1. Obstructions and foreign bodies
   • If a dog were to inhale an object into the trachea the result is wheezing on inhalation if lodged in the upper airway and on expiration if lodged in the chest. It would be persistent and would not come and go and could also be very dramatic with ragged breathing, coughing, gagging and agitation. These are potentially serious emergencies and warrant immediate attention by a veterinarian. Radiographs are useful, but sometimes sedation and scoping would be needed for diagnosis and removal. There are some cases where surgery may be necessary.
2. Heart disease
   • Coughs caused by heart disease are often very gradual in onset, but because they can be hidden for so long, they can appear in what seems like a sudden onset. Heart disease causes a cough in 2 ways: either fluid build-up in the lungs (pulmonary edema) or compression of the main-stem small airways from heart enlargement. Diagnosis is by x-ray and auscultation of the chest. Ultrasound is the best test to evaluate the heart and is always indicated if heart disease is present.
   • Treatment varies depending on the nature of the disease, but can often involve the use of diuretics to remove the fluid if present and certain cardio-protective medications that depend on the nature of the heart disease on ultrasound.
3. Kennel cough
   • Kennel cough is a term we use to describe a cough caused by an infection. Most are contracted from direct contact with an infected dog. The name comes from the fact that these kinds of infections thrive in a kennel environment. However, dogs can contract them at a dog park, with a dog walker, or even at a groomer.
   • There are several viruses and one species of bacteria that are likely to cause the infection. A dog can get a combination of infections (referred to as a respiratory complex) as the bacteria, Bordetella, is very good at colonizing a respiratory tract already compromised by a viral infection. Most episodes of kennel cough last for 1-2 weeks, but if Bordetella is present, the cough and secondary effects (fever, lethargy and poor appetite) can be much more severe.
   • The infections can be definitively diagnosed by a viral PCR swab, and bloodwork and x-rays can be useful to rule out other causes for a cough. Note that the early stage of the infection can cause a great deal of gagging – ulceration of the throat and mucus production can be quite severe and result in a dog that gags repeatedly, in some cases bringing up foam and bile, for the greater part of 24 hours.
   • There is no specific treatment for the viral infection beyond supportive care (rest, good nutrition and in some cases a cough suppressant). If Bordetella is present, then an antibiotic is indicated.
4. Allergic airway disease
   • There are a large number of specific allergic reactions throughout the respiratory tract, but in the case of a cough, the most common is allergic bronchitis. Any air impurity that irritates the small airways in the lungs will result in a reaction that produces swelling around and fluid within them. The fluid makes it more difficult for the dog to breathe and as it is moved up into the larger airways it produces a cough and a gag. The inflammation will also contribute to the coughing.
   • These forms of bronchitis are very common in elderly dogs and diagnosis is based on a combination of auscultation, x-rays and ideally a microscopic analysis of a sample from the lower airways.
   • There are number of treatment options for allergic bronchitis, and no one treatment is perfect for all cases. Once a diagnosis is made, then we often attempt some trial therapies to find the right balance.

From this discussion, I hope you will understand that the diagnosis and management of a cough in a dog can be complex. There is a big difference in a dog that suddenly starts coughing as compared to a dog that has been coughing for several weeks and kennel cough is very common. However, it can be dangerous to get tunnel vision when dealing with a cough – the safest medicine is always to take a broad-based diagnostic approach and to get a physical examination and some tests done. Serious diseases can be managed much more effectively if found in the early stages.

by Dr. Gawen Thompson