Pneumonia
TEXTBOOK OF VETERINARY INTERNAL MEDICINE
Client Information Series Dr Alfred M. Legendre
Pneumonia is an inflammation of the lungs. It is rare in cats and less common in dogs than in people. There are many types of pneumonia, with bacterial and fungal infections being the most common.
The dog's lungs are not very susceptible to primary bacterial pneumonia, but prior lung damage predisposes them to secondary invasion by bacteria. The canine distemper virus causes severe damage to the cells lining the respiratory tract of dogs, making the lungs more susceptible to bacterial infection and pneumonia.
A common type of pneumonia is aspiration pneumonia, which occurs when dogs vomit and inhale that material into their lungs. Aspiration may occur when animals vomit after surgery because anesthetic drugs depress the swallowing reflexes.
Aspiration pneumonia may be caused by a condition called megaesophagus. In megaesophagus, there is abnormal movement of the esophagus (the tube that connects the mouth with the stomach), allowing food to accumulate instead of moving into the stomach. This pool of food and saliva is constantly regurgitated into the mouth and some of the material goes down the trachea into the lungs. Some diseases of the nerves that control swallowing can also allow entry of food into the lungs. The inhaled food contains bacteria and sometimes stomach acid that cause inflammation.
Dogs with pneumonia are usually brought to the veterinarian because of coughing, loss of appetite, depression, and difficulty breathing. They often have a fever. Lung sounds heard with a stethoscope are increased because of the abnormal pus and fluid in the airways.
The effort required to breathe gives an indication of the severity of the lung infection.
Identification of the cause of the pneumonia is necessary for optimal treatment. Chest radiographs (x-rays) are required for accurate diagnosis of pneumonia. Fungal pneumonias have a typical pattern of inflammation that helps differentiate them from bacterial pneumonia. In megaesophagus, there is an enlarged esophagus and the lung inflammation occurs in the lower part of the lungs. Diagnosis of bacterial
pneumonia secondary to distemper is difficult. Additional tests for distemper should be done in dogs whose vaccinations are not current. Bacterial pneumonia can also be secondary to tumors and foreign bodies, such as pieces of grass.
A complete blood count is helpful in assessing the severity of the lung inflammation and identifying secondary diseases. Obtaining pus and fluid from the airways is important in identifying the organism causing the problem. The type of bacteria and its antibiotic sensitivity determine the antibiotic needed. People can cough up a sputum sample for testing, but dogs are not as cooperative. A procedure known as a percutaneous (going through the skin) tracheal washing is an effective and relatively safe way to obtain material from the trachea and bronchi. A local anesthetic in the skin allows painless passage of a small tube through the skin of the neck into the trachea or windpipe. Fluid is injected through the tube to dilute the thick material in the airways, which can be sucked into a syringe. During the 2 to 3 days required for the bacterial test to be completed, an antibiotic likely to be effective may be started. This antibiotic may need to be changed when the culture results are obtained.
Antibiotics or antifungal drugs are the mainstay of bacterial and fungal pneumonia treatment, respectively. Dogs with severe respiratory difficulties may require oxygen treatment to improve their breathing. Nebulization of a fine water mist can help keep the airway moist, loosen thick mucus, and help the lungs remove debris through coughing.
The outcome of pneumonia in dogs depends on the cause of the pneumonia and the severity of the infection. There must be enough lung capacity to maintain an adequate oxygen supply to the body for at least 2 to 3 days until the antibiotics can begin to work.
Primary pneumonias without underlying disease are usually treated successfully. The prognosis for aspiration pneumonia depends on the ability to correct the cause of the vomiting and on the severity of the pneumonia. Pneumonias secondary to distemper or similar viral diseases have a guarded prognosis. At least half of dogs with distemper develop seizures because of the effects of the virus on the brain.
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