The term pneumonia in dogs means inflammation of the functional tissue of the lungs and lower respiratory tract. Usually, it is accompanied by inflammation of the upper airways to varying degrees. Although experts vary slightly in their exact definitions of the upper and lower respiratory tracts, it is generally accepted that the upper respiratory tract includes the nasal cavities, pharynx (throat), larynx, trachea ("windpipe") and bronchi. The lower respiratory tract is made of the bronchioles and alveoli of the lungs. In dogs, the lungs are divided into deeply fissured lobes. The left lung has three lobes (cranial, middle and caudal), and the right lung has four lobes (cranial, middle, caudal and accessory).
Causes of Pneumonia
Pneumonia can be caused by a number of things, including viruses, bacteria, fungi and internal parasites. Infection of the nasal cavity and other parts of the upper airways often precedes pneumonia in domestic dogs, as well as in people. Pneumonia associated with any infectious organisms can be "caused" - or contributed to - by anything that compromises a dog's immune status or otherwise predisposes the dog to developing inflammation of the lower respiratory tract. Pneumonia in adult dogs is almost always associated with some predisposing abnormality. This can be administration of chemotherapeutic medications, chronic systemic illness, laryngeal paralysis, gastroesophageal reflux disease, respiratory tract tumors, megaesophagus, malnutrition, stress, tumors, parasitic infection, inhalation of foreign bodies, chronic bronchitis (inflammation of the bronchi), esophagitis (inflammation of the esophagus) collapsing trachea, pyloric output obstruction or long-term treatment with corticosteroid drugs.
Most cases of bacterial pneumonia are caused by bacteria from the oral cavity (mouth) and pharynx (throat) that enter the lungs through the upper airways and settle in certain areas of the lungs by reason of gravity. Pneumonia caused by bacteria that reach the lungs through the blood supply (hematogenously) usually is more diffuse throughout all of the lung lobes. Suspected bacterial organisms include Escherichia coli, Klebsiella, Proteus, Streptococcus, Staphylococcus, Bordetella bronchiseptica and Pasteurella, among others. Bacterial pneumonia often develops secondary to viral pneumonia, because the dog's defenses are weakened.
Two of the more common causes of viral pneumonia are canine distemper virus and canine influenza virus. Canine adenovirus Type 1 and the parainfluenza virus can also infect the lower respiratory tract, although the signs of pneumonia associated with those viruses usually develop from secondary bacterial infections.
Aspiration pneumonia, also called inhalation pneumonia, is caused by the inhalation or aspiration of infected solid or liquid material into the lungs. It can result from any disorder that adversely affects a dog's respiratory defenses or increases the risk of aspiration. This can include diseases of the pharynx, larynx, esophagus, stomach or intestine. Laryngeal paralysis, gastroesophageal reflux disease, megaesophagus, tumors, paralysis of the complex swallowing mechanism, esophagitis, pyloric output obstruction and trauma, as well as reflux of stomach contents into the lungs due to vomiting, regurgitation or induction of general anesthesia, all are risk factors for aspiration pneumonia. It can also be precipitated by inhalation of smoke, mineral oil, kerosene, gasoline or other caustic chemical substances. Disorders that cause states of altered consciousness or chronic vomiting can also predispose a dog to developing aspiration pneumonia.
Preventng Pneumonia in Dogs
One of the key ways to prevent pneumonia is to address and resolve any predisposition conditions, such as gastric reflux disorders, laryngeal paralysis or pyloric outflow obstructions. Other important suggestions are to fast dogs for 12 hours before they are put under general anesthesia, to prevent vomiting and aspiration of stomach contents. Antacids may be appropriate to reduce gastric reflux in dogs with that condition. Force-feeding should only been done when necessary for the dog's health, and even then it should be done cautiously.
Dogs in severe respiratory distress should not be given cough suppressants, because coughing is the body's normal response to try and clear the airways and help the dog breathe.
Pneumonia is not particularly common in healthy mature dogs. It is more often a disease of the very young, the very old and those with weak or compromised immune systems. When it does occur, pneumonia can be acute (come on suddenly) or chronic (come on slowly). The main functions of the lungs are to supply the blood with oxygen inhaled from outside air, and to dispose of carbon dioxide waste in exhaled air. When signs of pneumonia are present, they are attributable to insufficient intake of oxygen and inefficient oxygen exchange and delivery to body cells, both of which are caused by inflammation and irritation of airway and lung tissue and by mucus build-up in the respiratory tract.
Symptoms of Pneumonia in Dogs
Dogs with pneumonia may never show signs of their disease. When symptoms are present, they may include one or more of the following:
Rapid breathing (increased respiratory rate; tachypnea)
Deep breathing (increased respiratory depth)
Difficulty breathing (dyspnea; labored breathing; respiratory distress on inspiration and exhalation)
Cough (usually soft, wet, bubbly and productive)
Nasal discharge (usually bilateral [coming from both nostrils] and thick with mucus and pus)
Chest congestion (wheezes and crackles detectable on auscultation [listening through a stethoscope])
Lack of appetite (inappetence; anorexia)
Rapid heart rate (tachycardia)
Unusual stance – head lowered, front legs splayed at the elbows
Bluish discoloration of the skin and mucous membranes (cyanosis)
Dogs at Increased Risk
Young puppies and old dogs are the most common targets of pneumonia. Newborn puppies are vulnerable to developing aspiration pneumonia, especially if they are bottle-fed or if they have cleft palates. Any dog that is force-fed also has an increased chance of developing aspiration pneumonia. Dogs with damage to or diseases of the throat, trachea, esophagus, stomach, airways or lungs may have an increased risk of developing pneumonia, as do dogs whose immune systems are compromised for any reason.
How Pneumonia is Diagnosed
Pneumonia is not especially difficult to diagnose, as long as the appropriate diagnostic tools and owner willingness are present.
When presented with a dog in respiratory distress, a veterinarian will take all necessary steps to ensure that the patient has a patent airway. Once that is accomplished, she will conduct a thorough physical examination and take a complete history from the owner. The initial data base typically includes routine blood work (a complete blood count [CBC] and serum biochemistry panel) and a urinalysis. The results of these preliminary tests may or may not be abnormal. Even if they are normal, pneumonia cannot be ruled out.
The next diagnostic step is to take thoracic radiographs (chest X-rays), from several different views. Chest films usually are diagnostic of the existence of pneumonia, but they cannot help identify the cause of the dog's condition. Definitive diagnosis of the actual cause of the lung infection usually is made by collecting, examining and culturing blood samples. The results of advanced blood work should identify the specific microorganisms that are involved and provide guidance to the veterinarian in selecting the most appropriate antibacterial, antiviral, antifungal, antiparasitic or other treatment protocol.
Another common diagnostic tool is transtracheal lavage. This is a respiratory wash procedure that involves flushing the trachea with a sterile solution, drawing the fluid and dislodged airway cells back into a syringe and submitting the sample to a diagnostic laboratory for assessment and culture. Arterial blood gas analysis and pulse oximetry can be used to evaluate the levels of oxygen in the blood (this is called oxygenation). Bronchoscopy is a technique whereby the veterinarian inserts a wand-like instrument with a camera at its tip down the trachea and into the upper bronchi, enabling her to visualize the respiratory lining and remove any reachable foreign bodies that may be obstructing the upper airways. Tumors can also be seen and biopsied using this technique. Computed tomography (CT scan) is available in some specialized clinics but usually is unnecessary if good quality chest radiographs are taken.
Pneumonia is not extremely common in adult companion dogs. When it does occur, it often is discovered incidentally to some other condition or disease.
Dogs with signs of severe respiratory distress need immediate veterinary attention. Treatment goals are to ensure proper oxygenation of circulating blood, resolve any primary and secondary infections, remove any lodged foreign bodies, restore the dog's health and comfort, eliminate any predisposing conditions and prevent recurrence if at all possible.
The treatment protocol for a dog with pneumonia will depend on the cause of the infection. In cases of aspiration pneumonia, the treatment team can use suction to extract the aspirated material from the upper airways, if that is where they are lodged. Periodic oxygen supplementation using an oxygen mask or cage can help relieve severe respiratory distress. If the dog is dehydrated, intravenous fluids, either with or without added electrolytes, can be administered. Increasing the moisture content of the air in the treatment room can be done with a humidifier. Bed rest and good supportive care are always important to the dog's successful recovery.
Bacterial pneumonias are treated with antibiotic medications selected based upon the results of blood culture and sensitivity testing to identify the exact microorganisms causing the infection. Even if the primary cause of pneumonia is not bacterial, many veterinarians recommend a full course of broad-spectrum antibiotics, because secondary bacterial lung infections are extremely common. The oral antibiotic regimen usually continues for 3 or 4 weeks, and at least 1 week after clinical signs and radiographic evidence of respiratory disease have normalized.
A number of different oral bronchodilators are available to ease the dog's breathing. Affected dogs that are recumbent (lying down) should have their position physically changed every few hours, to prevent fluid from accumulating in particular lung lobes. In some cases, surgical removal of damaged lung tissue may be necessary, especially if the infection does not respond well to medical therapy. This procedure is called a lung lobectomy.
Dogs with pneumonia caused by viral, fungal or parasitic infection will be treated with medications specific to the cause of their disease. The attending veterinarian is in the best position to discuss the appropriate treatment protocol with the owners. Of course, any conditions that predispose a dog to pneumonia, such as gastroesophageal reflux disorders or laryngeal paralysis, should be addressed to reduce the risk of recurrence.
The prognosis for dogs with pneumonia depends upon the cause and severity of the dog's disease. Dogs with uncomplicated pneumonia generally have a good prognosis. Most cases of bacterial pneumonia are successfully treatable. Acute-onset aspiration pneumonia accompanied by severe respiratory distress has the potential to be fatal. If the underlying cause of the pneumonia is not identified and corrected, recurrence of the disease is likely.