The cat liver fluke is a hepatic fluke, which means it affects the bile duct, small intestines, pancreatic duct and liver. Without treatment, liver fluke can be fatal. Outdoor cats and feral cats who hunt are more susceptible to contracting the fluke.

Liver fluke infestation in cats occurs when the Opisthorchis felineus, or cat liver fluke, infects the cat from a secondary host. The parasite lives in warm, freshwater lakes and rivers in subtropical areas, such as Hawaii, Florida, Central America, parts of Asia, Italy and eastern Europe. The small parasite typically first infests cyprinid fishes and snails. Other animals, such as frogs, lizards or larger fish, eat the infected fish or snail, becoming the second intermediate host. When the cat eats the second intermediate host, it becomes infected with the parasite.

Most cats with cat liver fluke present with no symptoms (asymptomatic). When cats become heavily infected, however, they may display the following symptoms:

Liver fluke infestation is caused when an infected cat passes feces that contains the embryonated eggs that have fully-developed miracidium, or larvae. These eggs are then consumed by a snail, where the miracidia emerge from the eggs and enter the snail's intestine. The larvae, now know as cercariae, are released from the snail, and they are consumed by a larger fish, frog or lizard. When an outdoor cat hunts and eats these animals, the cercariae enter and dwell in the upper digestive tract and bile ducts. It takes approximately eight weeks for the parasite to mature and shed eggs, which then pass into the cat's feces, perpetuating the cycle. Cats who live in tropical and subtropical areas and who live outdoors are most likely to contract the parasite. It is estimated that 15 to 85 percent of cats who live in infested areas have contracted the parasite at some point in their lives.

The veterinarian will need to know the cat's complete health history, what symptoms are present and when symptoms first began. Cat liver fluke is often suspected with cats who live in areas where the fluke dwells, are allowed to go outdoors, and present with typical symptoms. The veterinarian will run routine labs, such as a biochemical profile, complete blood count, and a urinalysis. These labs can help the veterinarian determine how the liver is functioning and rule out other conditions with similar symptoms.

The veterinarian will confirm the diagnosis of cat liver fluke by taking a sample of the bile or liver tissue. These samples will be sent to the lab in order to look for the presence of the fluke. The veterinarian may also take a stool sample in order to look for fluke eggs in the feces. Because it takes eight weeks for the parasite to mature and pass eggs, however, the cat could potentially become very ill by the time eggs are present in the feces.

Cats who are dehydrated as a result of vomiting and diarrhea will need to be hospitalized in order to receive intravenous fluid therapy. The veterinarian will monitor the cat's labs during fluid therapy to ensure they are being well-received by the cat's body.

If the cat is unable to eat, a feeding tube may be inserted directly into the cat's intestines. This feeding tube will be placed through the cat's nose or via a small incision in the esophagus. 

The veterinarian will prescribe a medication, such as fenbendazole or praziquantel, to kill the parasitic worms. If the cat is hospitalized, this medication will be given intravenously. Cats who are being treated an outpatient basis will receive an oral medication. Vitamin D may be given to the cat intravenously to help promote healing. The veterinarian may also place the cat on an antibiotic in order to prevent infections from occurring.

On rare occasions, the parasite can block the cat's bile ducts, preventing the bile from entering the small intestine to aid in digestion. In this case, surgery may be necessary to clear the bile ducts.

The cat will need to follow up with the veterinarian for the monitoring of liver enzyme levels. Because liver fluke can cause carcinomas in the liver or pancreas, it is important to watch for symptoms of these conditions, such as loss of appetite, weight loss, and jaundice. With prompt treatment, most cats recover completely from liver fluke infestation.