Feline Infectious Peritonitis (FIP) in Cats | Pets Best

Getting the news that a beloved cat has feline infectious peritonitis (FIP) is heartbreaking. Recently there have been advancements in the treatment, but FIP is still nearly always fatal. A new, successful treatment approved in 2021 in the U.K.1 is currently undergoing trials in the United States.2 Even with treatment, FIP can be a long and arduous battle for cat parents and their precious felines. But now there’s hope.

What is FIP?

FIP stands for feline infectious peritonitis, which is caused by a feline coronavirus. This coronavirus is actually quite common among cats, and most have been exposed to it at some point in their lives.3 Cats usually just have mild diarrhea or no sickness at all from it.4 However, in a small percentage of cases, the coronavirus mutates into a more dangerous strain and spreads throughout the body, causing significant inflammation.

This feline coronavirus is in the same family as the COVID-19 coronavirus, but they are very different viruses, causing completely different diseases and infecting completely different species.3

So, can a cat get COVID? Yes, in some situations, but it’s not the same as the cat coronavirus that causes FIP. Feline coronavirus infects wild and domestic cats, but FIP isn’t contagious to humans or other animals. In fact, while coronavirus is contagious, FIP itself isn’t contagious to other cats.5

If one cat in a household has FIP, the other cat cannot catch it. Certainly, the coronavirus itself is contagious, but the virus responsible for FIP has to mutate in the patient’s body to cause this disease. This is a rare example of an infectious disease that really isn’t contagious in the usual sense.5

What are the risk factors of FIP?

The feline coronavirus that can lead to FIP lives in a cat’s intestinal system and is typically spread through contact with feces.3 Cats that share litter boxes are at an increased risk of becoming infected. Less often, FIP can also be transmitted through saliva, sneezing, sharing a food bowl or mutual grooming.6

Cats are at higher risk for feline infectious peritonitis if they are young, or if they have a compromised immune system or an underlying chronic disease. While outdoor and indoor cats of any age are at risk, FIP is more commonly seen in cats aged 6 months to 2 years, and in certain purebred breeds.6

Feline infectious peritonitis symptoms

As the cat’s body responds to the virus, inflammation from the immune response can affect just about any organ system. As a result, depending on the organ system affected, the symptoms of FIP can vary from nonspecific signs like lethargy and not eating to seizures, blindness and trouble breathing, to name a few.7

There are traditionally two forms of the disease: wet FIP and dry FIP.6 But often, infected cats have symptoms of both. Early clinical signs may include loss of appetite and energy or a fluctuating fever.After that, more serious FIP symptoms develop (depending on which organs are infected), including:6

  • Fluid buildup in the abdomen or chest6
  • Difficulty breathing4
  • Seizures and uncoordinated movement4
  • Weight loss, vomiting or diarrhea6
  • Excessive thirst or urination4
  • Lesions around blood vessels4
  • Changes in the eyes, like bleeding or pus in the globe6
  • Jaundice4

Diagnosing FIP

FIP is a very challenging disease to definitively diagnose since there is no one FIP-specific test.3 The diagnosis is best made using a combination of methods along with history and physical examination findings.

If a cat has the effusive (wet) form of FIP, a diagnosis is easier.3 A veterinarian can test a sample of the fluid in the abdomen or chest for the presence of high levels of protein, which is typical for FIP.

For cats with the non-effusive (dry) form of FIP, diagnosis is tougher since the symptoms are often vaguer and can mimic other diseases. Remember, there is no single blood test for FIP. Rather, a battery of tests may be run to rule out other causes.3 Veterinarians may also look for a pattern of changes in routine bloodwork that point to FIP.Other possible tests include brain MRIs, cerebrospinal fluid samples, tissue biopsies or looking for the virus in areas of inflammation.

However, your veterinarian may be wary of ordering a test that requires anesthesia in order to diagnose FIP. Any severely ill cat (from FIP or otherwise) may be at greater risk of death from anesthesia.9

FIP treatment

Currently, only traditional treatments aimed at reducing the immune response toward FIP and symptomatic therapies aimed at alleviating clinical signs are approved in the United States. FIP still carries a poor long-term prognosis for survival, but more successful treatments are currently being studied in clinical trials.2 These treatments are also already approved in some other countries and show some promise.1

So, how long can a cat live with FIP? Without treatment, most cats will only have a life expectancy of a few weeks or months.6 But newer FIP treatments are leading to remission, and thus longer life spans.

Traditional FIP treatment

Traditional FIP treatment focuses on easing symptoms, but it doesn’t cure the devastating illness.4 Sometimes this supportive care can extend the cat’s life by a few months, especially if started early while your cat is still in relatively good condition and not in the final stages of FIP.6 It involves treatments to help your cat feel better, such as appetite stimulants, antibiotics for secondary bacterial infections, and even draining fluid from around the lungs to ease breathing or giving blood transfusions in the case of severe anemia.4

Newer FIP treatments

In recent years, the treatment for FIP has changed drastically. Some antivirals have been shown to have the potential to cure FIP through a long dosing regimen. In fact, veterinarians in the U.K. and Australia have been able to prescribe these medications since 2021.10 However, they aren’t yet approved by the FDA in the United States.As a result, some U.S. cat owners may try to purchase them on the black market. However, it’s impossible to test the quality of medicine bought this way, and the medicine itself can be very expensive.3

The antivirals are GS-441524 (oral tablets) and remdesivir (IV or subcutaneous injection). In the U.K., veterinarians prescribe these with a minimum course of 12 weeks. So far, more than 85% of treated cats have achieved long-term remission, which is amazing considering the disease was previously almost always fatal. In a few cases, some cats may relapse and need repeat treatment.1

In the U.S., clinical trials are underway for testing GS-441524 and remdesivir in cats.2 A Bengal cat named Lily is in remission after participating in one of those trials at the UC Davis veterinary hospital.2 A kitten named Gridley is also in remission after getting 92 days of treatment from UC Davis.11

Here’s what you can do to help prevent FIP

While there is a vaccine for FIP, the American Association of Feline Practitioners doesn’t recommend it.3 The vaccine can only be used starting when a kitten is 16 weeks old. But the feline infectious peritonitis virus is so common that by the time a cat can get the vaccine, he’s likely already been exposed to the virus.

Without a vaccine, the next best course is to do all you can to prevent FIP from developing. This can include preventing overcrowding of cats and keeping litter boxes clean and away from food and water dishes.4 Because stress can play a role in diminishing the immune system—leaving it vulnerable to developing FIP—it’s a good idea to keep your cat as healthy and stress-free as possible.8

Final thoughts

Feline infectious peritonitis is a devastating disease that can develop from what is usually a benign coronavirus infection. You’ll want to do what you can to try to prevent this illness, including keeping your cats healthy, happy and living in a hygienic environment. If your precious kitty does develop FIP and you’re in the United States, you may want to talk to your veterinarian about enrolling in a clinical trial for one of the antivirals that are approved in the U.K. and Australia.

From Pets Best

Pets Best insurance plans can help you prepare for the unexpected, including testing and treatments for your cat if you’re worried your pet may have a coronavirus infection or FIP. Pets Best policyholders can also speak to a veterinary expert anytime through a 24/7 Pet Helpline if they have concerns.


1Sorrell, Dr. Stephanie et al. (2022, May.) Feline Infectious Peritonitis (FIP) Information for Cat Owners. International Cat Care. Retrieved from https://icatcare.org/app/uploads/2022/05/FIP-pet-owner-brochure-FINAL-V2-1.pdf.

2Warren, Rob. (2022, December 29.) Clinical Trial Places Cat’s FIP in Remission. UC Davis Veterinary Medicine. Retrieved from https://www.vetmed.ucdavis.edu/news/clinical-trial-places-cats-fip-remission.

3Mitchell, Sandra C., DVM, DABVP. (2022, January 24.) Feline Infectious Peritonitis (FIP) in Cats. PetMD. Retrieved from https://www.petmd.com/cat/conditions/infectious-parasitic/c_ct_feline_infectious_peritonitis.

4(2021, February 12.) Cat FIP (Feline Infectious Peritonitis): Symptoms, Causes, and Treatments. Fetch by WebMD. Retrieved from https://pets.webmd.com/cats/cat-fip-feline-infectious-peritonitis.

5Addie DD, Jarrett O. Feline Coronavirus Infections. Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis. Elsevier Saunders. 2006. pp. 88-102.

6Levy, Julie K., DVM, PhD, DACVIM et al. (2022, October.) Feline Infectious Peritonitis (FIP.) Merck Veterinary Manual. Retrieved from https://www.merckvetmanual.com/cat-owners/disorders-affecting-multiple-body-systems-of-cats/feline-infectious-peritonitis-fip.

7Little, Susan, DVM, DABVP. (2017, October 7.) FIP: Update on Diagnostics and Treatment Options. 22nd Annual ABVP Symposium.

8(2022, May 17.) Feline Infectious Peritonitis (FIP) (feline coronavirus.) International Cat Care. Retrieved from https://icatcare.org/advice/feline-infectious-peritonitis-fip/.

9Pedersen, Niels C., DVM, PhD. (2021, June 1.) The Neurological Form of Feline Infectious Peritonitis and GS-441524 Treatment. UC Davis. Retrieved from https://ccah.vetmed.ucdavis.edu/sites/g/files/dgvnsk4586/files/inline-files/The%20neurological%20form%20of%20FIP%20and%20GS%20treatment%20June%202021_0.pdf.

10Imrie, Paul. (2022, April 29.) Vet Help Sought for FIP Treatments Study. VetTimes. Retrieved from https://www.vettimes.co.uk/news/vet-help-sought-for-fip-treatments-study/.

11Serrin, Greta. (2022, March 20.) Miracle Kitten: Placer County Veterinarians Successfully Treat Cat for Type of Deadly Feline Coronavirus. KCRA 3. Retrieved from https://www.kcra.com/article/placer-county-veterinarians-successfully-treat-deadly-feline-coronavirus/39479223.

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