Liver Fluke in Cats: Platynosomiasis

What are liver flukes?

A liver fluke is a type of parasitic worm called a trematode. Platynosomum fastosum (also known as P. concinnum, P. illiciens) is the species that infects the liver of cats in tropical and subtropical regions. There are other types of liver flukes in different parts of the world. This species of fluke causes a disease called platynosomiasis. Cats infected with this disease develop signs of liver and gallbladder disease. This disease cannot be transmitted to people. 

What is the lifecycle of a liver fluke?

The lifecycle is complex and involves several stages and hosts. 

1. Affected cats shed eggs in their feces. 
2. The eggs are eaten by snails and then develop into sporocysts containing cercariae (larvae).
3. The snails are ingested by lizards, amphibians, or isopods (pill bugs), which are the second intermediate hosts. Inside the second host, the cercariae develop into metacercariae (infective larvae).
4. Cats are infected by ingesting the second intermediate host, which is why the disease is sometimes called “lizard poisoning”.

In the cat’s liver, the metacercariae mature into adult flukes, which live in the bile ducts and gall bladder. The flukes lay eggs that travel to the intestines, along with bile, to be released in the feces, and the cycle begins again.

Where are liver flukes found?

Platynosomum spp. are found in tropical and subtropical regions, including the Caribbean, Central and South America, Southeast Asia, and West Africa. In the United States, they have been found in Florida and Hawaii. No sex or breed predisposition has been found. Cats that go outdoors and hunt in these regions have a higher risk of infection.

What are the symptoms of liver flukes?

Symptoms of liver flukes mimic those of other types of liver disease and range from mild to severe. Thickening and distension of bile ducts by the adult flukes can lead to blockage of bile flow, fibrosis of the liver (cirrhosis), and liver failure. 

Non-specific symptoms include 

• vomiting
• diarrhea
• weight loss
• poor appetite
• increased drinking and urination
• dehydration

More severe signs include: 

• yellowing of the skin and gums (called jaundice or icterus)
• abdominal pain
• abdominal distension
• enlargement of the liver

How is the disease diagnosed?

Diagnosis is not always straightforward. Finding eggs in a fecal sample indicates the disease is present, but standard fecal testing can miss the eggs. Using a special sugar solution increases the likelihood of finding the eggs.

If your cat has clinical signs consistent with this disease, your veterinarian will likely recommend additional testing, starting with bloodwork. A complete blood count may show increased eosinophils, which are white blood cells that are often elevated with parasitic disease. 

The biochemistry profile often shows elevated liver values, including bilirubin. Bilirubin is a substance produced when red blood cells break down. It should be eliminated by the liver through the bile, but when bile flow is compromised, it builds up in the body. Bilirubin is yellow and causes jaundice. Other changes may include elevated kidney values, evidence of pancreatitis, and changes in blood proteins.

Imaging with X-rays does not often help with diagnosis, whereas ultrasound may show dilated bile ducts, a distended gall bladder,  changes in liver texture, and rarely adult flukes.  A sample of bile from the gall bladder can be collected with an ultrasound-guided needle and examined for eggs. Egg counts may be higher in bile than in feces.

A liver biopsy may show evidence of adult flukes, but more often, changes in the bile duct system can be diagnostic.

Diagnosis is often presumed based on a combination of clinical signs, supportive blood testing, imaging, and your geographical location, as infection is more likely to occur in certain locations.

What is the treatment?

There are no commercial products specifically labeled for the treatment of liver flukes, but several treatments have been successful. Praziquantal and Fenbendazole are two antiparasitic drugs that have been effective. In severely affected cats, treatment may not improve clinical signs, as the damage to the liver is irreversible, and may worsen as the flukes die.

Other treatments for liver disease include nutritional and fluid support, pain medications, anti-nauseant medications, antibiotics for secondary infections, and a medication called Ursodiol to help improve bile flow. If the gallbladder is completely obstructed, surgical removal can be considered, though the prognosis is poor in this case.

What is the prognosis?

The prognosis is variable and depends on how severely affected the cat is. If clinical signs are mild and caught early, prognosis is good. Prognosis is more guarded if bile duct obstruction and liver failure are present; in this case, it can lead to death.