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.