Dogs get pneumonia through several routes: inhaling infectious agents like viruses or bacteria, aspirating vomit or stomach acid into their lungs, or breathing in fungal spores from contaminated soil. The most common starting point is a viral infection of the lower respiratory tract, which damages the airway lining and opens the door for bacteria to settle in. Some dogs are also at higher risk because of their breed, anatomy, or existing health conditions.
Viral Infections That Lead to Pneumonia
Viruses are the single most common cause of pneumonia in dogs. Canine distemper virus, adenovirus types 1 and 2, canine influenza virus, and parainfluenza virus all attack the lower airways, damaging the protective mucous membranes that line the bronchial tubes. Once that lining is compromised, bacteria that would normally be filtered out can colonize the lungs and trigger a deeper, more dangerous infection.
This is why what starts as a mild cough or runny nose can escalate into pneumonia within days. The virus itself may not cause life-threatening illness, but the secondary bacterial infection it enables often does. Dogs that are very young, elderly, or immunocompromised are especially vulnerable to this progression.
How Aspiration Pneumonia Happens
Aspiration pneumonia develops when a dog inhales foreign material, most often stomach acid or vomit, into the lungs. The inhaled material carries bacteria from the mouth directly into the small air sacs (alveoli) where gas exchange happens. Those bacteria then multiply in the warm, moist lung tissue, causing inflammation and infection.
Most cases happen when a dog vomits and accidentally breathes some of that material in. If your dog coughs right after vomiting, that can be a sign stomach acid has irritated the lungs. But vomiting isn’t the only trigger. Dogs can also aspirate during anesthesia, while eating or drinking too quickly, or if they have a condition that impairs their ability to swallow properly.
Esophageal disease is considered the most important underlying cause of aspiration pneumonia in dogs. When the esophagus doesn’t move food toward the stomach correctly, food or fluid can slip into the airway instead. One study found that 62% of dogs with esophageal dysfunction experienced gastroesophageal reflux, which was directly linked to a higher risk of aspiration.
Fungal Pneumonia From Soil Exposure
Dogs can also develop pneumonia by inhaling fungal spores from contaminated soil. The fungi enter through the respiratory tract and cause fever, coughing, lethargy, and pneumonia-like symptoms. Several species are responsible, but the most clinically significant ones thrive in specific environments: river valleys, wooded areas, and regions with moist, organic-rich soil.
Unlike bacterial or viral pneumonia, fungal pneumonia is not contagious between dogs. A dog picks it up by digging, sniffing, or simply walking through areas where the fungus lives in the ground. Dogs that spend a lot of time outdoors in endemic regions are at the greatest risk.
Where Dogs Catch Infectious Pneumonia
The infectious forms of pneumonia spread most easily in places where dogs gather closely together: shelters, boarding facilities, doggy daycares, and dog parks. Respiratory pathogens travel through coughs and sneezes, but also through contaminated objects. Canine influenza virus, for example, can survive up to 48 hours on hard surfaces, up to 24 hours on clothing, and up to 12 hours on human hands.
That means shared water bowls, leashes, collars, and bedding can all serve as transmission vehicles. People can carry the virus between dogs simply by petting an infected animal and then touching a healthy one. Facilities with poor ventilation or high dog turnover, like intake shelters, see the highest rates of respiratory outbreaks.
Breeds and Conditions That Raise the Risk
Flat-faced (brachycephalic) breeds like Bulldogs, Pugs, and French Bulldogs face a significantly elevated risk. Research published in JAVMA found that the risk of aspiration pneumonia in brachycephalic breeds was nearly four times higher than in other dogs. The reason is partly structural: their compressed airways create extreme negative pressure in the chest during breathing, which increases the likelihood of stomach acid being pulled back up into the esophagus and then inhaled. Endoscopic exams of brachycephalic dogs with upper airway disease found gastrointestinal abnormalities in 97% of cases, including reflux, hiatal hernias, and pyloric stenosis.
Large-breed dogs with laryngeal paralysis, a condition where the muscles that open the airway become weak or paralyzed, are another high-risk group. The most common cause of laryngeal paralysis is a broader nerve disorder (polyneuropathy), which can also affect the esophagus. Dogs with megaesophagus, where the esophagus loses its ability to push food down, had roughly 2.5 times the risk of developing aspiration pneumonia compared to dogs without it.
Other risk factors include chronic vomiting, neurological conditions that affect swallowing, and any situation involving general anesthesia, since a sedated dog’s protective reflexes are suppressed.
Signs to Watch For
Pneumonia in dogs typically shows up as a persistent wet or productive cough, labored breathing, nasal discharge, fever, lethargy, and loss of appetite. You might notice your dog breathing faster than usual at rest or using more visible effort with each breath, with the belly pushing in and out noticeably. Some dogs will sit with their neck extended and elbows turned outward, a posture that helps open the airways.
These signs can develop gradually over several days with bacterial or fungal pneumonia, or appear suddenly in the case of aspiration. If a dog vomits and then within hours becomes lethargic, starts coughing, or shows labored breathing, aspiration pneumonia is a strong possibility.
How Vets Confirm the Diagnosis
Chest X-rays are the primary tool. Veterinarians look for areas of cloudiness or increased density in the lung fields, which indicate fluid or inflammatory material filling the air sacs. Each lung region is scored based on how much tissue is affected, from mild (under 25% of a lobe) to severe (over 75%). Multiple X-rays over time help track whether the infection is improving or spreading.
In some cases, vets will also collect a sample of fluid from the airways to identify the specific bacteria or fungus involved, which guides treatment decisions.
Treatment and Recovery
Bacterial pneumonia is treated with antibiotics, and the course length depends on how quickly the dog responds. Many dogs also receive supportive care to help clear their lungs. Nebulization delivers medicated mist directly into the airways, often containing anti-inflammatory drugs or bronchodilators that widen the air passages. Coupage, a technique where you gently but firmly pat the dog’s chest with cupped hands, helps loosen mucus trapped deep in the lungs so the dog can cough it up more effectively. This is something owners can learn to do at home.
Dogs with severe pneumonia, particularly aspiration cases, often need hospitalization for oxygen support and intravenous fluids. A study of 88 dogs hospitalized with aspiration pneumonia found that 77% survived and were discharged. Survival rates were consistent regardless of how many underlying conditions the dog had or how many lung regions were affected, which suggests that prompt treatment matters more than the initial severity of the X-ray findings.
Fungal pneumonia requires a different approach, with antifungal treatment that can last weeks to months depending on the organism and how widespread the infection has become. Recovery is slower, and dogs often need repeated imaging to confirm the infection has resolved.
Reducing Your Dog’s Risk
Keeping vaccinations current is the single most effective prevention strategy for infectious pneumonia. Vaccines exist for canine distemper, adenovirus, parainfluenza, and canine influenza, all of which are common precursors to bacterial pneumonia. If your dog frequents boarding facilities or dog parks, the canine influenza and Bordetella vaccines are especially relevant.
For dogs prone to aspiration, feeding from an elevated position can help reduce reflux. Dogs with megaesophagus are often fed in a special upright posture (sometimes called a “Bailey chair”) and kept vertical for 10 to 15 minutes afterward to let gravity move food into the stomach. Managing chronic vomiting and treating underlying gastrointestinal disease also lowers the risk substantially. If your dog is a brachycephalic breed, corrective airway surgery can reduce the breathing obstruction that contributes to reflux and aspiration.