The Most Common Causes of Pneumonia in Pets

Pneumonia is a clinical respiratory illness that can involve various elements. In the following article, we'll analyze the most common causes of pneumonia in pets.
The Most Common Causes of Pneumonia in Pets

Last update: 19 September, 2020

Many readers may have gone to the veterinarian recently because their pet was experiencing respiratory problems. In general, most of these situations resolve themselves easily since the pathological processes they involve aren’t usually serious. Coughs or tracheitis are the most common respiratory illnesses. However, on occasions, the situation can worsen and lead to pneumonia. There are many diverse causes of pneumonia in pets, which we’ll look at in the following article.

What is pneumonia?

Pneumonia includes all of those clinical processes that produce the inflammation of lung tissue. When bronchial tissue also becomes swollen, then the clinical term is bronchopneumonia.

Distinguishing between pneumonia and bronchopneumonia is complicated and also unnecessary. Often, when this illness occurs, it affects all of the lung parenchyma and the bronchial tissue indistinctly

The causes of pneumonia in pets

The causes of pneumonia in pets are varied. However, we want to concentrate on the most important and frequent, which often represent the cause of most cases of pneumonia.

Bacterial pneumonia

Bacterial pneumonia is an inflammatory response to the growth of virulent and pathogenic bacteria in the lung parenchyma.

These bacteria penetrate the upper respiratory airways through respiration or aspiration. Hematogenous entry–through the bloodstream–is also possible, but much less frequent.

At this point, it’s especially relevant to mention pneumonia by aspiration. This occurs frequently as a result of the aspiration of vomit and regurgitation in animals that have fainted. In order to prevent this complication, it’s vitally important to position animals with their back third slightly elevated. This will help keep them from aspirating regurgitated fluids.

Once the microorganisms settle in, a series of factors must fall into place in order for infection to develop. That’s because the body’s own natural defenses, on many occasions, take on the bacteria that have colonized the area.

Inmunodepression, concomitant illnesses like diabetes and kidney problems, especially virulent bacteria, and malnutrition are some factors that negatively influence the establishment of this illness.

The most common pathogens when it comes to bacterial pneumonia in pets are:

  • Bordetella bronchiseptica
  • Streptococcus zooepidemicus
  • Escherichia coli
Bacterial infections in pets.

Allergic pneumonia

This type of pneumonia consists of the inflammation of the lung parenchyma in response to certain antigens.

As many readers know, allergies are no more than an exaggerated immune system response to a substance it recognizes as dangerous. Therefore, when the allergen enters the lung, the organism identifies it as a threat and produces a reaction to eliminate it at all costs.

The most frequent agents behind allergic pneumonia are:

  • Vegetable spores
  • Fungus hyphae
  • Insect antigens, like mites
  • Parasite antigens

Fungal pneumonia

This is an inflammation of the lung tissue produced by a reaction to a fungal infection. The way it enters the respiratory system occurs through the inhalation of spores present on the ground.

When animals sniff the ground, the may inhale pathogenic spores that colonize and reproduce in the lung parenchyma. Once inside the body, the temperature and humidity conditions there are perfect for the growth of these fungi. Given their habits, dogs are more likely to suffer from this type of pneumonia than cats.

The most common fungi behind cases of fungal pneumonia in pets are the following:

  • Blastomyces dermatitidis
  • Histoplasma capsulatum
  • Coccidioides immitis
  • Cryptococcus neoformas
A cat with pneumonia.


The body’s defenses are capable of combating most of the pathogens that can cause pneumonia in pets. However, we can’t forget the fact that the risk still exists. Early detection is fundamental when it comes to the prognosis and development of this pathology.

Therefore, if you notice even the slightest symptom of respiratory illness, like frequent coughing or sneezing or mucous, you should contact your veterinarian.

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