CONDITION
Pneumonia
Pneumonia is inflammation of the lung tissue, most often involving bacterial infection. It is a common diagnosis in dogs, frequently following inhalation of food, vomit or regurgitated material, a viral or bacterial respiratory infection such as kennel cough, or an inhaled foreign body such as a grass awn. It occurs less often in cats, and laboured breathing in a cat is more often due to heart failure, which can look very similar from the outside. Signs range from a moist cough, quietness and poor appetite to laboured breathing. Fever is detected in only around 16 to 50 per cent of cases, and a cat's cough can be mistaken for retching, so the absence of either does not rule pneumonia out. Chest X-rays are central to confirming it, although changes can lag behind the signs. Some forms, including a haemorrhagic streptococcal pneumonia seen in dogs, can progress to severe illness or sudden death.
Why this matters now
Pneumonia can develop at any age but may be more severe in very young, elderly, or immunocompromised animals. The condition often follows respiratory infections, anaesthesia, vomiting episodes, or underlying diseases that compromise normal lung defences. In dogs with aspiration pneumonia, the underlying problems most often involved are oesophageal disease such as megaoesophagus, vomiting, neurological disorders, laryngeal disease and recent anaesthesia. Bordetella bronchiseptica, one of the organisms involved in kennel cough and in feline respiratory disease, can occasionally spread from animals to people.
Early pneumonia may present subtly with mild cough and reduced energy. Without treatment, infection spreads through lung tissue, filling airways with inflammatory fluid and debris. Breathing becomes progressively laboured as functional lung capacity decreases, and blood oxygen can fall before this looks dramatic: in one study of dogs with aspiration pneumonia, 79 per cent of those tested had low blood oxygen. The pace varies. Some cases develop over days, whilst aspiration pneumonia can appear suddenly after vomiting, regurgitation or anaesthesia, and haemorrhagic pneumonia caused by Streptococcus equi subspecies zooepidemicus can lead to sudden death. Animals that do not improve with oxygen can tire and go into respiratory failure. Between 77 and 94 per cent of animals diagnosed with pneumonia are discharged from hospital, which also means a meaningful minority are not.
Signals & patterns
Early signals
Soft, moist cough
A productive-sounding cough that differs from the dry cough typical of kennel cough. In cats, coughing can be mistaken for retching or an attempt to bring up a hairball.
Nasal discharge
Mucoid or discoloured discharge from the nose may accompany lung infection.
Reduced activity
Affected animals often become quieter and less interested in usual activities.
Mild fever
A raised temperature can reflect the body's response to infection, but fever is detected in only around 16 to 50 per cent of cases, so a normal temperature does not rule pneumonia out.
Decreased appetite
General malaise typically reduces interest in food.
Rapid, shallow breathing
Cats in particular may breathe faster, with short, shallow breaths, sometimes without any obvious cough.
Later signals
Laboured breathing
Increased respiratory effort with visible chest or abdominal movement, and in cats flared nostrils.
Open-mouth breathing
Particularly concerning in cats, indicating significant respiratory compromise.
Bluish gums
Cyanosis reflects inadequate oxygen levels in severe cases.
Abnormal lung sounds
Crackles and other abnormal lung sounds are usually detected with a stethoscope rather than heard at home; they were present in 68 per cent of dogs in one study of aspiration pneumonia.
Weakness or collapse
Profound weakness, collapse or an inability to settle can reflect falling oxygen levels or infection spreading into the bloodstream (sepsis).
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis combines physical examination findings with imaging and sometimes sampling of airway secretions to identify the cause and guide treatment.
Chest radiographs
Blood tests
Pulse oximetry
Tracheal wash or bronchoalveolar lavage
Arterial blood gas
Options & trade-offs
Treatment focuses on addressing infection, supporting breathing, and managing underlying causes, with intensity depending on severity.
Antibiotic therapy
Targeted antimicrobial treatment based on likely or confirmed bacteria
Trade-offs: Needed where bacterial infection is present; courses of 4 to 6 weeks were traditionally used without evidence to support that length, and current guidance is to reassess no later than 10 to 14 days after treatment starts, with the total length then judged on how the animal is doing, on blood results and on repeat X-rays; may require culture-guided changes. Not every aspiration event involves infection at first; some cause chemical injury to the lung, which can later become infected.
Oxygen supplementation
Provides enriched oxygen for animals struggling to breathe
Trade-offs: Life-supporting in severe cases; requires hospitalisation; enables recovery while lungs heal.
Nebulisation and coupage
Moisturising airways and chest physiotherapy to help clear secretions
Trade-offs: Supports airway clearance; can be continued at home; requires patient cooperation.
Fluid therapy
Intravenous fluids to maintain hydration and support circulation
Trade-offs: Important for animals not eating; must be balanced against fluid overload in lungs.
Treatment of underlying cause
Addressing conditions that predisposed to pneumonia
Trade-offs: Reduces the chance of recurrence; may include managing regurgitation, laryngeal function, or immune disorders.
Common misconceptions
"Pneumonia only occurs in cold, wet weather"
While environmental factors can contribute, pneumonia develops from infections or aspiration regardless of season.
"A pet with pneumonia will always cough dramatically"
Some animals, particularly cats, may show subtle signs like reduced activity and mild breathing changes rather than obvious coughing.
"Antibiotics produce an instant recovery from pneumonia"
While improvement often begins within days, recovery commonly continues for some time after signs settle, and an animal that is not improving within the first days of treatment is typically reassessed.
Related conditions
Feline Asthma
Feline asthma and pneumonia both involve inflammatory processes affecting the respiratory tract, though asthma typically causes reversible airway narrowing whilst pneumonia involves infection and consolidation of lung tissue. Cats with chronic airway inflammation may occasionally develop secondary bacterial pneumonia.
Megaoesophagus
Megaoesophagus can predispose dogs to aspiration pneumonia when regurgitated material enters the airways, making it one of the more common underlying causes of recurrent or persistent lung infection in affected animals.
Laryngeal Paralysis in Dogs
Laryngeal paralysis increases the risk of aspiration pneumonia in dogs. Many affected dogs also have oesophageal dysfunction as part of a wider, progressive nerve disorder, and aspiration pneumonia is a recognised complication after surgery to open the larynx, reported in almost a quarter of dogs in one large study.
Feline Herpesvirus (FHV-1)
Feline herpesvirus typically causes upper respiratory signs, but in young kittens or immunocompromised cats the infection can occasionally extend to involve the lower airways and lung tissue, resulting in viral or secondary bacterial pneumonia.
Lymphoma in Dogs
Lymphoma in dogs can occasionally involve the lungs directly or compromise immune function systemically, predisposing affected animals to opportunistic respiratory infections including pneumonia.
Aspiration Pneumonia
Aspiration pneumonia is the form that follows inhalation of food, vomit, regurgitated material or liquid, and is one of the most common types in dogs. It is usually linked to an underlying problem that affects swallowing, the larynx or consciousness.
Infectious Tracheobronchitis (Kennel Cough)
Kennel cough is usually confined to the windpipe and larger airways, but organisms involved in it, such as Bordetella bronchiseptica and Mycoplasma, can progress to bronchopneumonia in some dogs. A cough that becomes moist, together with lethargy, poor appetite or faster breathing, differs from the pattern of uncomplicated kennel cough.
Angiostrongylus (Lungworm)
The lungworm Angiostrongylus vasorum, present in the UK, can cause coughing and breathing difficulty in dogs that resemble pneumonia, and can also cause bleeding problems. Specific tests for lungworm are used alongside chest imaging to separate the two.
Hypertrophic Cardiomyopathy in Cats
In cats, heart failure is a more frequent cause of laboured breathing than pneumonia; in one study, 65 per cent of cats presenting in respiratory distress had heart failure. The two can look alike from the outside and are separated by examination and imaging, and many cats with cardiomyopathy have no murmur.
Congestive Heart Failure in Dogs
Heart failure with fluid in the lungs can cause coughing and faster, laboured breathing in dogs that resembles pneumonia. Chest X-rays, and sometimes heart ultrasound, are used to tell the two apart.
Bordetella in Cats
Bordetella bronchiseptica infection in cats ranges from mild upper respiratory signs to severe pneumonia with laboured breathing and blue-tinged gums. It is regarded as a rare cause of zoonotic infection in people.
Pyothorax
In cats, pyothorax most often arises when bacteria from the mouth and upper airways colonise the lung and spread into the chest cavity, so pneumonia and pyothorax can be linked. Pyothorax typically involves chest drainage and flushing alongside antibiotics.
Laboured breathing while resting, visible abdominal effort with each breath, open-mouth breathing in a cat, or grey or blue-tinged gums indicate that oxygen exchange is already impaired, and how far oxygen levels have fallen cannot be judged at home. Fever and cough are poor guides: many dogs with pneumonia have a normal temperature, and a cat's cough can be mistaken for retching. A cough or change in breathing shortly after vomiting, regurgitation or an anaesthetic fits the pattern of aspiration, and in a dog with megaoesophagus or laryngeal paralysis that link is well recognised. Several conditions look similar from the outside and are separated with examination and chest X-rays, including heart failure, which is the more common cause of laboured breathing in cats, fluid around the lungs, feline asthma and, in the UK, lungworm infection in dogs. Recent vomiting, kennelling, anaesthesia and any known underlying conditions are useful context for that assessment.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS