Fungal Infection (Pneumocystosis) of the Lung in Cats

By PetMD Editorial on Mar. 17, 2010

Pneumocystosis in Cats


Pneumocystosis is a respiratory infection involving Pneumocystis carinii, a fungus commonly found in the environment. Although pneumocystosis  may lead to a variety of health issues, it only affects dogs (or humans) with compromised immune systems because the weakened body defenses allows the P. carinii organism to multiply and grow to critical levels in the lungs.


Symptoms and Types


Generally, the breathing difficulties will progressively worsen over a four-week period. Other signs associated with pneumocystosis include:





Pneumocystosis is caused by an overabundance of the P. carinii fungus in the respiratory system, typically found in immune-compromised cats.




You will need to give a thorough history of your cat’s health, including the onset and nature of the symptoms, to your veterinarian. He or she will then perform a complete physical examination, as well a biochemistry profile, urinalysis, and complete blood count (CBC) -- the results of which are usually non-specific and may show increased number of leukocytes or white blood cells as seen in infections, increased number of eiosinophils, and increased number of red blood cells. Blood gases testing, meanwhile, may reveal decreased partial pressure of oxygen in blood (hypoxemia), and increased pressure in blood pH. Thoracic X-rays are also conducted to see the severity and stage of the infection, as related to the lungs.

For definitive diagnosis, however, your veterinarian will take a respiratory fluid sample or tissue sample to a pathologist to test for abnormal levels of P.carinii. Although it is the most reliable method for verifying pneumocystosis, lung biopsies are not without complications. Moreover, few diagnostic kits are available.



Hospitalization and intensive care is required in severe cases. This may include oxygen therapy to minimize respiratory discomfort and prevent further decrease in the blood's oxygen level, and antibiotics to control infection. In these cases, cats are kept in isolation to minimize exposure to other pathogens. Physical therapy may also be used to promote the removal of secretion from the lungs, while intravenous fluids are used to correct dehydration.


Living and Management


Prognosis will ultimately depend on the disease that has caused the immunodeficiency. However, it is generally promising in less severely affected patients that have undergone treatment early.


Regular monitoring of blood gases, pulse, and thoracic radiography is required to monitor the cat's response to the treatment. In addition, you should restrict the cat's activity level to a minimum and allow it to rest in a cage. If you should notice any signs of a deteriorating condition, such as coughing, respiratory discomfort, etc., call your veterinarian immediately.

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