Lung flukes are oval, reddish-brown, and fleshy parasitic worms that are found in cysts primarily in the lungs of felines. However, in rare cases, the parasites can migrate and reside in the viscera or brain of the cat. The term veterinarians use for a fluke is Trematode. The trematode life cycle begins as the eggs are hatched underwater and evolve into miracidium, which will infect its first intermediate host, the snail. The trematode will remain inside the snail until it matures into the cercarial stage. The cercaria will then leave its first intermediate host and proceed to its second host, the crayfish or crab, maturing into metacercarial form. The metacercarial stage is the infectious stage, in which when a feline consumes the host housing the fluke and becomes infected. The parasites are ingested, reach the intestines and then make their way to the lungs where they will multiply.

Lung flukes are a type of parasitic worm that infects the respiratory tract of cats. There are two main varieties of lung flukes to infect felines, Paraonimus westermani and Paragonimus kellicotti. A feline can become infected with one of these flukes by ingestion of the intermediate host, which can either be a variety of snail, crab, or crayfish. It stands to reason that feline infections are common in geographical areas that support snail, crab or crayfish dietary needs. Therefore, feline fluke infestations are most common in areas of North America, Southeast Asia and China. Once the flukes are ingested and migrate into the lower respiratory tract, the feline will develop a deep, chronic cough as the primary symptom. 

Lung flukes pass through the feline’s diaphragm and into the lungs where they will feed, breed, and lay eggs. The eggs that are laid will pass through the cyst wall, which the feline will cough up and swallow again. Therefore, the eggs will be digested, pass through the feces and can be seen under microscopic view. The infected feline may develop a deep, chronic cough, but many lung fluke infections go unnoticed by cat owners. Symptoms that cat owners should watch for to suggest a lung fluke infection in their cat include: 

A lung fluke infection in cats is caused by consuming the first or second intermediate host of the parasite. A feline who eats a raw snail, crayfish, or crab infected with the lung fluke will directly infect herself. The fluke is ingested, migrates to the lower respiratory system where the parasite will feed, mate, and lay eggs to be shed in the feces. Lung flukes are a common occurrence in stray felines in parts of North America, China, and Southeast Asia.

Diagnosing a cat with lung flukes is accomplished by running a number of diagnostic tests to exclude other diseases that resemble the clinical signs associated with lung flukes. Heartworms, for exam, are another parasite that has a higher contraction report than lung flukes and therefore a heartworm test will be performed for excluding purposes. The veterinarian will begin by taking a completed medical history and physical exam of the feline, which will include a stethoscope lung auscultation. Additional tests that the veterinarian will likely conduct to diagnose lung flukes in cats include: 

Unlike intestinal parasites, flukes are less buoyant and therefore a regular fecal flotation test may prove inefficient. Therefore, a special fecal sediment test is performed called the Baermann technique is used to identify fluke ova or larvae. 

A process used to collect respiratory secretions from the feline in order to identify fluke ova or leave. 

An x-ray of the feline’s chest cavity may reveal pulmonary cysts created by the harboring lung parasites. 

Although there are no parasitic products designed especially for lung fluke infections, the veterinarian will likely prescribe a treatment off-label. There are a number of drugs that have been proven highly effective treatment against trematodes, though fenbendazole is usually recommended in felines. Your veterinarian may refer to these drugs as “de-wormers” and prescribe the best choice of anti-parasitic medication to suit your feline’s condition. 

Cats infected with lung flukes recover within a few weeks after treatment is administered. The medication actively kills the flukes inside the feline and they are then shed through the feces or coughed up. Therefore, it is highly recommended that the feline’s environment stay clean and isolated from other pets. The litter box, food and water bowls should receive special attention to avoid re-infection.