Pneumonia Due to Overactive Immune Response in Dogs

By PetMD Editorial on Sep. 14, 2010

Eosinophilic Pneumonia in Dogs

The term pneumonia refers to an inflammation of the lungs. The lungs can become inflamed as the result of many conditions. One of these is antigens -- foreign substances that generate an immune response in the body, leading to an abnormal accumulation of a type of white-blood cells called an eosinophil. They also become more active in response to parasites in the body. Ideally, eosinophils help the body to fight against the antigens or parasites that the body is attempting to eliminate or neutralize. An antigen may enter the body through inhalation, ingestion, or other known pathways into the system (e.g., bite wounds, injuries).

In eosinophilic pneumonia, an increased number of eosinophils and fluid accumulates in the lung tissue, as well as in the various airway channels and tiny sacs within the lung tissue where the oxygen and carbon dioxide are exchanged, resulting in swelling of the lung tissues, inflammation, and decreased breathing capacity.

Symptoms and Types

Symptoms related to this disease are extremely variable in different animals depending on the severity of the disease. The most common symptoms include:

  • Cough that is not responding to antibiotic therapy
  • Difficult breathing
  • Exercise intolerance
  • Fever
  • Lack of appetite
  • Lethargy
  • Weight loss
  • Yellow or green pus in the nasal discharge


This type of pneumonia is more commonly seen in dusty or moldy environments, or in areas with high air pollution. Other underling factors include:

  • Pollen allergy
  • Insects
  • Parasites (heartworm)
  • Infection


You will need to give your veterinarian a thorough history of your dog’s health, including a background history of the symptoms and when they became apparent. After taking a detailed history, your veterinarian will conduct a complete physical examination on your dog. Laboratory tests will include a complete blood count (CBC), biochemistry profile, and urinalysis. Stool testing is also performed to determine whether a parasitic infection is present. The complete blood count test will reveal inflammation with an increased number of white blood cells, including neutrophils, eosinophils, basophils and monocytes (all of which are types of white blood cells). More advanced testing will include measuring the blood gases to evaluate the functioning ability of the respiratory system.

Your veterinarian will also take the fluid samples from the lungs, which can provide a definitive diagnosis by revealing the presence of inflammation along with a large number of eosinophils. Heartworm disease testing is also important, as this common disease can lead to eosinophilic pneumonia.

Diagnostic imaging of the lungs can be especially helpful in determining the extent and severity of the inflammation so that a prognosis can be made. Chest X-rays will show characteristic changes in the lungs related to this disease, including fluid that has collected in the lung tissue.

If your doctor suspects an allergen, skin testing may be done to determine the allergen, but it is often of little value and may only be ordered if all else has failed.


In case of severe disease, your dog will need to be hospitalized to stabilize its system. Intravenous fluids will be given to compensate for lost body fluids levels -- to reverse or prevent dehydration, which can quickly become life-threatening. In case of severe respiratory discomfort, oxygen will be given to relieve the dog from struggling. Medications can then be given to open the narrowed airways in order to facilitate normal breathing.

Drugs, such as steroids, are commonly used to reduce symptoms of inflammation. In severe cases, long-term therapy may be required over a few months. In some dogs with overactive immune reactions, immune-suppressive drugs may also be required.

In cases of heartworm disease, specific drugs are used to treat and eradicate the heartworms from the body. Heartworm treatment can be very dangerous for some dogs, so heartworm elimination should only be done under the guidance of a veterinarian.

In cases of fungal infections, antifungal drugs can be used to treat the disease. In more advanced cases with permanent damage or scarring of the lungs, surgery may be required to remove the affected part of the lung.

Living and Management

Complete rest is recommended for your dog while it is under treatment. Good caloric intake is of paramount importance for the recovery of your dog; your veterinarian can guide you on crafting a good diet for recovery and immune system health.

Breathlessness is the most common problem in these animals, and good home-care should be ensured to minimize the stress, with a quiet space to rest that is out of the way of daily foot traffic and away from main entryways. Your veterinarian will schedule a follow-up examination, with chest X-rays and laboratory testing to monitor your dog's physical response to the medications.

The prognosis for this this disease depends on the identification of the primary cause or allergen. However, if the allergen can not be identified, long-term palliative treatment may be required to control the symptoms. In case of progressive and chronic disease, the overall prognosis is often not very good.

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