What is the respiratory system?
In general terms, the respiratory system is divided into two parts. The upper respiratory tract consists of the nose, nasal sinuses, throat, and trachea (windpipe) while the lower respiratory tract consists of the small airways (bronchi and bronchioles) and the alveoli (the small air sacs deep in the lung tissue where oxygen exchange occurs).
What is pneumonia?
Strictly speaking, bronchopneumonia is an inflammation of both the lungs and the airways (bronchi and bronchioles), while pneumonia is an inflammation of the lungs or lower respiratory tract. However, the terms are often used interchangeably.
What causes pneumonia?
In general terms, inflammation in the lungs is the response of tissues or cells to injury, irritation, or infection.
More specifically, most cases of pneumonia in dogs are caused by a bacterial infection. The most common bacteria that cause pneumonia in dogs are Bordetella bronchiseptica, Streptococcus zooepidemicus, Pasteurella multocida, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Mycoplasma species.
B. bronchiseptica is highly contagious and may spread easily to other dogs. It usually causes 'kennel cough', an infection of the trachea and bronchi, but can spread deeper into the lungs, especially in young or old dogs, or dogs with a compromised immune system. Most other causes of bacterial pneumonia are not particularly contagious to other dogs.
Sometimes, dogs develop bacterial pneumonia as a secondary infection. In some of these cases, the primary or underlying cause is a viral infection such as influenza, parainfluenza, or canine adenovirus type-2. In other cases, irritants such as tobacco smoke, smog, or other inhaled pollutants may be the underlying cause that predisposed the dog to a bacterial infection.
Are there any risk factors for developing bacterial pneumonia?
Any disease or condition that affects the respiratory tract can predispose a dog to developing bacterial pneumonia. Some risk factors include conditions that cause difficulty swallowing or problems with regurgitation such as laryngeal paralysis, megaesophagus, cleft palate, chronic vomiting, altered states of consciousness, and tumors of the respiratory system.
Dogs with an immune system disease or those that are on immunosuppressive drugs are at an increased risk of bacterial pneumonia, as are dogs with severe metabolic disorders such as kidney failure, uncontrolled diabetes mellitus, Cushing's disease, or Addison's disease.
What are the signs of bacterial pneumonia?
Dogs that have bacterial pneumonia usually:
- have a high fever
- have difficulty breathing
- have decreased exercise tolerance (tire easily)
- are lethargic
- have a cough
Other signs that may be present include a nasal discharge, loud breathing, rapid breathing, weight loss, anorexia, and dehydration.
Could these signs be caused by something else?
Some of these signs are common and are not specific to any one disease. Non-infectious respiratory disease such as chronic obstructive pulmonary disease (COPD), heart disease causing pulmonary edema, and lung cancer can also cause some of these symptoms. Before reaching a diagnosis of bacterial pneumonia, your veterinarian will conduct a thorough physical examination and recommend a series of diagnostic tests.
How is bacterial pneumonia diagnosed?
Your veterinarian may suspect bacterial pneumonia based on the presence of the signs listed above, combined with the results of a physical examination, especially if abnormal lung sounds are heard when listening to your dog’s chest with a stethoscope.
A series of tests may be required to confirm the diagnosis and to exclude other diseases that could be causing the symptoms, including:
- CBC and biochemistry profile. These blood tests will assess the general health of your dog, and specific blood or fecal tests may be recommended to rule out parasitic diseases such as heartworm or lungworm. Specific blood tests to rule out serious metabolic diseases may be necessary.
- Thoracic radiography (chest X-ray). Radiographs often show characteristic changes in the lungs, and may be helpful to eliminate other types of heart or lung disease.
- Cytology using bronchoscopy. A small fiber optic camera called a bronchoscope is used to directly examine the inner surfaces of the airways in an anesthetized dog. After completing the visual examination, cytology samples (samples of the cells lining the bronchi and bronchioles) can be collected for microscopic examination and for bacterial culture and sensitivity testing.
- Tracheal lavage. The pet is usually placed under sedation or anesthesia, and a thin, flexible, sterile catheter is passed into the area being investigated. A small amount of sterile fluid is flushed forcefully into the area and then promptly suctioned or aspirated back out. The recovered fluid contains mucus and a small number of cells that can be cultured for microorganisms and examined under the microscope.
What is the treatment for bacterial pneumonia?
The appropriate antibiotic treatment is determined by the results of the culture and sensitivity tests. These tests identify the specific bacterial species causing the infection and which type of antibiotics will combat this infection. Since the results of culture and sensitivity testing will not be available immediately, your veterinarian may begin treatment with a broad-spectrum antibiotic, such as doxycycline or amoxicillin, while awaiting the test results. It may be necessary to change the medication once the results are available. Your veterinarian will choose the appropriate antibiotics for your dog's particular situation.
"Medications may be required for a prolonged period of time, depending on the specific type of infection and the seriousness of the condition."
If your dog has respiratory distress or is dehydrated or anorexic (complete loss of appetite), hospitalization for oxygen therapy and/or intravenous fluids and medications may be necessary.
If your dog is stable enough to be treated as an outpatient, your veterinarian may also prescribe bronchodilators, expectorants, or other medications to control specific symptoms. Medications may be required for a prolonged period of time, depending on the specific type of infection and the seriousness of the condition.
Your veterinarian may also recommend several daily sessions of brief exercise to help loosen secretions and promote coughing out of inflammatory debris. Apart from these short sessions, your dog's activity should be restricted. Another helpful home treatment is to place the dog in a closed bathroom with a warm shower running for about 15 minutes up to 3 times per day. This increase in humidity has the effect of thinning out the mucus in the airways so that it is coughed up more readily (see handout "Techniques for Nebulization and Coupage in Dogs" for more information).
What is the prognosis for bacterial pneumonia?
The prognosis depends on the severity of disease and whether there are any predisposing factors. The prognosis is generally good for uncomplicated bacterial pneumonia. The prognosis for animals with predisposing factors depends on whether the risk factor can be treated or resolved. If the risk factors cannot be resolved, recurrent infections may occur. The prognosis for young or geriatric animals, patients with immunodeficiency diseases, or patients that are debilitated is guarded.