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Feline Infectious Peritonitis (FIP)

Written by Alyson Powell Key
Medically Reviewed by Amy Flowers, DVM on February 25, 2025
6 min read

Feline infectious peritonitis (FIP) is a viral disease caused by a feline coronavirus that affects wild and domestic cats. This type of coronavirus is different from the one that causes COVID-19 in people. FIP includes two forms: feline enteric coronavirus (FECV), which is common and usually mild, and feline infectious peritonitis virus (FIPV), which is much more dangerous.

Feline coronavirus is very common and usually doesn't cause any serious issues aside from mild diarrhea. But when the feline coronavirus changes to a specific strain of the coronavirus, it can cause FIP. The virus will multiply and mutate in about 10% of infected cats. The mutated form causes FIPV, leading to serious inflammation in the tissues around your cat's abdomen, including their kidneys or brain.

Although doctors don't believe FIP in cats is contagious, it's a serious disease. When a cat gets FIP, it gets worse and will likely kill them without treatment.

Feline enteric coronavirus, which causes FIP, mainly passes between cats through their environment and close contact. Here are the common ways it spreads:

From mother cat to kittens. This can happen through close contact between the mother cat and her kittens. It may be possible for the mother cat to spread FIP through her placenta to her unborn kittens, but more research is needed to confirm that. 

Poop. The virus spreads mainly through cat poop, especially when cats share the same litter box. 

Saliva. It can also spread through food bowls and when cats lick (groom) each other.

Sneezing. Though less common, sneezing might also spread the virus.

Short-term virus shedding. Most cats with the virus will shed it in their poop for a few months and then stop.

Long-term virus shedding. Some cats keep shedding the virus their entire lives.

Trisha Yarde, DVM, a hospitalist at CARE Veterinary Center in Frederick, Maryland, says FIP can happen to any cat, but some are more likely to get it. "It tends to be a little more common in purebred kitties," she explains. Yarde also says cats under age 2 and older than 13 have a higher chance of getting the disease. "The younger you are, the less efficient or complete the immune system. And the older we go, the immune system goes down. So the very young and the older tend to get it." 

Early signs of FIP in cats can vary but often include a rising and falling fever, loss of appetite, and energy loss. As time goes by, infected cats may have more FIP symptoms that depend on the form of FIP.

FIP has a "dry" and a "wet" form. Infected cats can have symptoms of only one form or a mix of both. 

Dry FIP. The dry form of FIP causes infections and inflammation. This can affect your cat's brain, eyes, liver, kidneys, lungs, and skin. Cats with this form often have seizures and may move in strange or uncoordinated ways. They might also drink and pee a lot, throw up, lose weight, and get jaundice.

Wet FIP. This form of the disease causes fluid to collect in the belly, giving the cat a pot-bellied look. Fluid can also gather in the chest, making it hard for the cat to breathe. Wet FIP harms the blood vessels, leading to inflammation and fluid leaking from the blood into the abdomen and chest.

Once a cat has FIP in either form, the symptoms tend to get worse with time. Without treatment, euthanasia (or putting the cat "to sleep") is often necessary in a matter of weeks or months.

FIP is hard to diagnose. Many of its symptoms could also be symptoms of other health issues in your cat. No single blood test is available to confirm FIP. Your veterinarian is more likely to assume FIP is present if your cat:

  • Has a low number of lymphocytes, a type of white blood cell
  • Has an unusually high number of neutrophils, a type of white blood cell
  • Has increased levels of protein in the blood
  • Shows yellowing of the gums or eyes
  • Belongs to a high-risk group (young cats or cats living in an overcrowded environment)

If there is a buildup of fluid in your cat's abdomen or chest, your veterinarian may collect a fluid sample for testing. Fluid with a high protein percentage indicates FIP and will frequently be yellow-tinged. If FIP is suspected, your veterinarian may take an X-ray or ultrasound of your cat.

A few other tests may help support an FIP diagnosis. The immunoperoxidase test can detect white blood cells infected with the virus. Vets also use polymerase chain reaction technology to test for the virus in tissue or body fluid. Sometimes, they may perform a biopsy of the infected tissue inside the abdominal cavity. 

Although these tests can help support a veterinarian’s diagnosis, none of them is 100% accurate.

FIP was long considered an untreatable disease until recently when the FDA approved drugs to help treat it.

GS-441524 for FIP

GS-441524 is a tablet or liquid oral antiviral drug that may cure FIP. The standard treatment lasts 84 days, but research shows a shorter 42-day treatment might work just as well. Ask your veterinarian which is best for your cat.

"We don't have long-term studies of this [drug] since it has recently become FDA-approved," Yarde says. "But 84% to 85% of these kitties are surviving at least the first six months, which is a complete turnaround from just a year ago when 95% of these cats were dying."

Other FIP treatments may include supportive care, such as drainage of built-up fluid and blood transfusions. Talk to your veterinarian to help you decide the best treatment option for your cat.

While a FIP vaccine is available, researchers aren't sure if it works, and the American Association of Feline Practitioners Feline Vaccine Advisory Panel doesn't suggest it. While the vaccine may be safe, you should carefully weigh the pros and cons. Before starting any new vaccine or treatment, talk with your veterinarian.

Because FIP forms after the feline intestinal coronavirus mutates, the best way to protect your cat from FIP is to avoid the coronavirus's initial infection. To help avoid infection, veterinarians suggest the following:

  • Keep your cat as healthy as possible.
  • Keep their litter boxes clean.
  • Keep their litter boxes away from food and water dishes.
  • If you own multiple cats, keep a maximum of three cats in each room to avoid overcrowded living conditions. 

But following these steps doesn't guarantee your cat won't get FIP. Dealing with a sick cat can be scary. A veterinarian can help you figure out the best steps to take care of your cat.

  • FIP is a disease that affects cats, but not dogs. It's caused by a feline coronavirus.
  • FIP is caused by a coronavirus that spreads through cat poop, saliva, and shared litter boxes.
  • Dry FIP causes your cat to have inflamed organs and possibly seizures. Wet FIP triggers a buildup of fluid in your cat's chest or abdomen. If the fluid buildup is in your cat's chest, they may have breathing problems.
  • There wasn't a legal option for treating FIP in the U.S. until the FDA recently approved an antiviral drug called GS-441524.

Is FIP contagious to other cats?

Experts don't think FIP is contagious. But feline enteric coronavirus, which can turn into FIP, is contagious.

How long do cats live with FIP?

Cats with untreated wet FIP typically pass away within two weeks of diagnosis, while cats diagnosed with dry FIP may live for a few months.

Can dogs get feline infectious peritonitis?

No. FIP doesn't affect dogs, just cats.