Capillaria in Cats

Published May 29, 2024
A cat walks outside.

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In This Article


What Is Capillaria in Cats?

Capillaria are small parasitic worms that can affect many different types of animals. They aren’t very common in cats, but when they do get Capillaria, it’s usually the kinds that invade the bladder—Capillaria plica and Capillaria feliscati, which are also called Pearsonema plica and Pearsonema feliscati.

These Capillaria species collectively are called bladder worms because the adults attach themselves to the wall of the bladder (and occasionally the kidneys or other parts of the urinary tract), where they can cause inflammation and other health problems.

Cats with capillariasis (the disease caused by Capillaria worms) rarely get very sick. Still, the condition can become a medical emergency in the unlikely event that a cat develops a urinary blockage.

Symptoms of Capillaria in Cats

Many cats with Capillaria have no clinical signs at all. However, if a cat has a lot of bladder worms, you may notice symptoms such as:

Other health problems (feline idiopathic cystitis, for example) cause similar symptoms and are much more common than Capillaria in cats.

Causes of Capillaria in Cats

The life cycle of Capillaria in cats isn’t fully understood, but it’s thought to go something like this:

  1. A cat, dog, fox, raccoon, coyote, or other animal that has bladder worms releases capillaria eggs into the environment when they urinate.

  2. The eggs hatch, releasing larvae that are eaten by earthworms.

  3. The larvae mature within earthworms until they reach the stage that can infect a new host.

  4. A cat eats the earthworm (or parts of an earthworm) in one of three ways:

    • Directly

    • By eating another animal that has earthworms in their digestive tract

    • By licking debris that contains bits of earthworm off their coat and skin

  5. The larvae make their way through the wall of the cat’s intestines to the bladder, where they mature into adults that breed and release eggs in the cat’s urine.

How Veterinarians Diagnose Capillaria in Cats

Whenever a cat has urinary problems, a veterinarian will collect a sample of urine and run a urinalysis. Part of a urinalysis involves using a centrifuge to separate out bigger objects (like cells or eggs) and then looking at them under the microscope.

If a veterinarian sees Capillaria eggs during the urinalysis, they can easily diagnose the cat with bladder worms. A urinalysis can also be a part of wellness screening in cats, which is how a cat without symptoms may end up being diagnosed with capillariasis.

Bloodwork and other diagnostic tests may also be necessary to evaluate the cat’s overall health and plan appropriate treatment.

Treatment of Capillaria in Cats

Several anthelmintics (drugs that kill worms) are effective against Capillaria. The one most commonly prescribed is fenbendazole.

Fenbendazole is very safe but isn’t approved by the Food and Drug Administration (FDA) for use in cats. However, veterinarians can prescribe it off-label to treat bladder worms. Other medications such as ivermectin (usually given by injection) can also be effective.

Severe cases of Capillaria may cause a lot of inflammation in a cat’s bladder. A few days of treatment with an anti-inflammatory medication (prednisolone, for example) can keep cats comfortable as their bladder heals. Fluid therapy and other forms of supportive care may also be needed.

Recovery and Management of Capillaria in Cats

Cats who have Capillaria and receive appropriate treatment usually recover quickly. Give your cat their medications as instructed by your veterinarian and make sure that your cat is eating, drinking, and urinating normally.

Call your veterinarian if your cat’s symptoms get worse at any point or don’t start improving after a few days.

After the medications have had a chance to get rid of the Capillaria, your veterinarian may recommend a follow-up urinalysis to ensure that no more eggs are present in your cat’s urine.

This is especially important if your cat doesn’t have any symptoms associated with their bladder worms, because it's hard to determine if treatment has been effective in these situations.

Prevention of Capillaria in Cats

Preventing Capillaria in cats isn’t difficult. Eating earthworms or small pieces of earthworms appears to be the only way that cats can contract capillariasis.

Therefore, keeping cats indoors and away from earthworms is the best form of prevention. If your cat must go outdoors, your veterinarian may recommend that you give a deworming medication on a regular schedule to protect your pet from Capillaria and other internal parasites.

Capillaria in Cats FAQs

Are bladder worms contagious?

Bladder worms in cats are not directly contagious. It is thought that their immature forms (larvae) must spend time inside earthworms before they can infect other animals.

People can get capillariasis, but it is caused by a different species of Capillaria worm and has nothing to do with cats.

Jennifer Coates, DVM


Jennifer Coates, DVM


Dr. Jennifer Coates is an accomplished veterinarian, writer, editor, and consultant with years of experience in the fields of veterinary...

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