Your dog’s respiratory system consists of two different parts. The upper respiratory tract consists of the nose, nasal sinuses, throat and trachea. The lower tract includes the bronchi, bronchioles and alveoli in the lungs. Upper lung pneumonia, or bronchopneumonia, occurs when both sections of the respiratory system become involved. In dogs, bacterial bronchopneumonia is the most common cause, but various other causative agents exist.
Common bacterial causes of canine pneumonia include Bordetella bronchiseptica, Pasteurells multocida, Streptococcus zooepidemicus, Kiebsiella pneumonia, Pseudomonas aeruginosa, E.coli and Mycoplasma species. The majority of them do not cause contagious pneumonia. Bordetella bronchiseptica, however, is a contributing bacterium to canine kennel cough, a highly contagious condition that often spreads throughout kennels.
Often, canine viral infections progress to cause secondary bacterial pneumonia. Typical viral conditions that can lead to pneumonia include parainfluenza, canine adenovirus type-2, canine distemper and canine influenza.
Another cause of pneumonia in dogs is fungus. Fungus enters the respiratory system through inhalation and settles in the lungs, resulting in pneumonia. Common fungal causes include Aspergillus, Blastomyces, Histoplasma, Cryptococcus and Coccidioidomycosis immitis. While these fungi can affect any breed of dog, male dogs are often at greater risk of fungal pneumonia than females. German shepherds have shown an increased occurrence of Aspergillus infection.
Lungworms (Oslerus osleri) are parasitic worms dogs contract through contaminated water or dead infected animals. The parasite enters the body and settles into the trachea and lungs, leading to airway and breathing restriction. Complications from a lungworm infection can lead to bronchitis, emphysema and pneumonia.
Aspiration and Antigens
Aspiration pneumonia occurs when foreign matter, such as vomit, enters the lungs and causes inflammation. This often occurs as the result of pharynx abnormalities or neuromuscular disorders. Another possible cause of canine pneumonia depends on the dog’s environment. Eosinophilic pneumonia occurs when a foreign antigen enters the body, triggering an overactive immune response. This typically occurs in dusty or moldy environments, or areas with elevated air pollution. Pollen allergies can also cause this type of immune response and subsequent pneumonia.