Pneumonia Due to Overactive Immune Response in Dogs

Dogs can develop lung disease as a result of an overactive immune response to an antigen in the body. This is called allergic pneumonitis. It is typically characterized by an infiltrate of eosinophilic cells (a type of white blood cell that fights disease) in the lungs. Eosinophils can attack and destroy specific antigens, so they move to areas of the body which are at risk for infection. In this case however, the immune system is overacting and the eosinophils may infiltrate and limit the function of the lungs rather than directly fighting infection. Formerly this conditions was known as pulmonary infiltration with eosinophilia (PIE syndrome), but currently it is referred to as eosinophilic bronchopneumopathy (EBP). Dogs usually develop a chronic cough, breathing difficulties, and intolerance to exercise. A heartworm infection is one of the best known causes for EBP. In this case, the allergic reaction is caused by the presence of microfilariae (immature worms) in the lungs. Other parasites or bacterial infection can also be the root-cause of the overactive immune response that occurs with EBP, but more commonly the condition is idiopathic, either related to an unknown allergen or a self-perpetuating autoimmune response. EPB symptoms may vary in severity, from chronic bronchitis, to a type of pneumonia with crackles in the lungs and difficulty breathing. Very severe infection (usually related to heartworm) can develop nodules on the lungs and some of the alveoli may become non-functional, drastically reducing oxygen absorption. Most types of allergic pneumonitis respond to steroid treatment, so EBP is usually a treatable condition.

Dogs can develop pneumonia because of an allergic reaction in the lungs. Veterinarians call this eosinophilic bronchopneumopathy because it is characterized by high numbers of disease fighting white blood cells called eosinophils. Eosinophilic bronchopneumopathy can be caused by a parasite, a bacterial infection, or an unknown allergen.

See a veterinarian immediately if you notice any of the following symptoms in your dog.

• Chronic persistent cough
• Gagging or retching
• Greenish or yellow discharge
• Weight loss
• Fever
• Wheezing
• Labored breathing
• Abnormal lung sounds
• Intolerance to exercise
• Bluish tinge to mucous membranes

Types

• Eosinophilic bronchopneumopathy (EBP) ia a loosely defined group of diseases characterized by eosinophilia and eosinophilic infiltrates in the lungs
• Pulmonary nodular eosinophilic granulomatous syndrome is a very severe form of EBP in which eosinophilic infiltrates cause inflammatory nodules in the lungs

These are some of the conditions that could trigger EBP in dogs.

• Parasites (especially heartworm)
• Bacterial infection
• Fungal infection
• Virus
• External antigen
• Dusty or moldy environment
• Idiopathic
• Higher incidence in Siberian Huskies

The veterinarian will examine your dog’s symptoms and listen to his heart and lungs. Crackles and abnormal breathing will be even more obvious with a stethoscope. Bloodwork and urinalysis may not show any abnormalities. About 50-60% of dogs will have eosinophilia on a blood test, but EBP may be present even without high levels of eosinophils in the blood.

X-rays of the lungs will usually show some degree of infiltration depending on the severity of the problem. Fluid in the lungs and nodules will be visible if they are present. X-rays will also help to identify another condition that could be causing your dog’s illness, such as cancer, a foreign body or a different kind of lung disease.

Further tests will be aimed at pinpointing the cause of EBP. Heartworm testing and fecal examination for parasites are very important since these are commonly found with EBP. A fluid sample will be obtained from your dog’s lungs or bronchial tubes to evaluate for other infections or cytological changes. This can help the veterinarian determine if a known antigen is responsible for your dog’s EBP.

Preliminary treatment will be aimed at treating the symptoms. Dogs that are very ill will need additional oxygen. A glucocorticoid such as prednisolone is typically given for several weeks to help reduce lung inflammation. If the airways are severely constricted, a bronchodilator may also be necessary.

Melarsomine dihydrochloride is usually used to treat heartworm infection. This medication is an arsenical compound, and it is quite toxic in large doses. Dogs are given two injections twenty-four hours apart, or three injections over the course of a month. The veterinarian will wait until your dog’s respiratory symptoms are stabilized and make sure he is healthy enough for the treatment to be safe. 

Antibiotic and antifungal medications will also be prescribed if these infections are part of the problem. Appropriate antibiotics may be identified based on a lab analysis or the bacteria’s resistance level. Antibiotic treatment may be necessary before glucocorticoid medication is prescribed since steroids will limit the function of the antibiotic.

If no other cause is found, glucocorticoid treatment may be continued for several months to help eliminate the symptoms. The veterinarian will usually adjust the dose downward by 25-50% as soon as improvement is seen. Inhaled glucocorticoid may also be recommended as this type of treatment has less negative side effects. Many dogs with unknown allergies need life-long glucocorticoid treatment to control the problem.

If EBP has a treatable cause, dogs will often make a complete recovery. Very severe heartworm infections can end up being fatal, but if they are caught in time they are usually treatable. Monthly heartworm prevention medication is also available and is recommended for dogs in areas where heartworm is common. Unidentified immune responses often need lifelong medication. Steroid treatment will usually reduce your dog’s symptoms to a manageable level, but there are potentially long term side effects with this medication. Discuss the risks with the veterinarian, and make sure your dog is taking the lowest effective dose.