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Lung flukes are parasitic worms (trematodes). The most common lung fluke to affect cats in North America is Paragonimus kellicotti, also known as the North American lung fluke. Other species of lung flukes can infect cats in other areas of the world, but they are rarely found in North America.
The life cycle of a lung fluke is complex, requiring several hosts to mature from egg to adult. The following is a simplified version of the life cycle of a lung fluke:
The natural final host of this parasite appears to be the mink but other animals, including cats, can also become infected when they eat raw crayfish. The most common way a cat is infected is by eating infected crayfish, but cats can also be infected by eating animals that prey on crayfish, such as rodents.
Lung flukes can be found anywhere in North America but are more commonly located around the Great Lakes region and the midwestern and southwestern parts of the United States.
Cats living near streams are more likely to become infected. They are also found in other areas of the world, particularly in China and Southeast Asia.
The usual symptoms of a lung fluke infection are intermittent coughing or difficulty breathing. If a cat is infected with a large number of flukes, the cat may cough up bloody mucus or may develop pneumonia, pneumothorax (lung collapse due to air in the chest cavity outside the lungs), or bronchiectasis (damage to the bronchioles of the lungs that lead to thickening, widening, and scarring). Severely infected cats may become weak and lethargic. With mild infections, there may be no symptoms at all.
A lung fluke infection is diagnosed by detecting eggs in a sample of either feces or mucus that an infected cat coughs up. It can also be detected by analyzing a sample of material from the trachea and bronchi, through procedures called a “transtracheal wash” or “bronchoalveolar lavage”.
> "X-rays of the lungs of an infected cat usually reveal white spots in the lungs, > > which are consistent with fluke cysts."To detect eggs from this parasite, the sample must undergo special processing. Most veterinarians will submit suspect samples to a veterinary laboratory for a definitive diagnosis.
X-rays of the lungs of an infected cat usually reveal white spots in the lungs, which are consistent with fluke cysts. X-rays are useful to determine how many cysts are present and where they are located. Sometimes an asymptomatic cat will be diagnosed when X-rays are taken for other reasons.
Cats can develop a cough or difficulty breathing from many causes. Treatment depends on the cause. Diagnostic testing is necessary to differentiate the cause of a cat’s symptoms and to determine the appropriate treatment.
No commercial products are specifically labeled for treatment of lung flukes in cats, but there are several antiparasitic drugs that are effective for treating this infection. The preferred treatment for lung flukes in cats is the antiparasitic drug praziquantel or fenbendazole (Panacur™).
Most infections will clear up with the appropriate treatment.
No, the only way that people can be infected with lung flukes is to eat raw crayfish contaminated with lung fluke cysts.
© Copyright 2025 LifeLearn Inc. Used and/or modified with permission under license. This content written by LifeLearn Animal Health (LifeLearn Inc.) is licensed to this practice for the personal use of our clients. Any copying, printing or further distribution is prohibited without the express written consent of LifeLearn. This content does not contain all available information for any referenced medications and has not been reviewed by the FDA Center for Veterinary Medicine, or Health Canada Veterinary Drugs Directorate. This content may help answer commonly asked questions, but is not a substitute for medical advice, or a proper consultation and/or clinical examination of your pet by a veterinarian. Please contact your veterinarian if you have any questions or concerns about your pet’s health. Last updated on Mar 20, 2025.
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