Understanding Feline Infectious Peritonitis (FIP) in Cats

Author: K. Marie Altoby K Marie Alto Updated 13 min read


Words you never want to hear from your veterinarian, “it looks like FIP.” Many cat parents have never heard of this disease, and if you’re one of them, consider yourself lucky. While I was familiar with FIP, I was never expecting to have a kitten diagnosed with (until recently) a 100% fatal disease.

If you’re here because you’ve been given a firm or suspected FIP diagnosis, this post will give you a full understanding of what’s currently known about this terrible disease and what options you have for treatment.

Yes, I said treatment.

If your vet told you there is no treatment, they meant there is no FDA approved treatment, and we’ll get to that in a bit.

While this post will focus on educating you about the disease, I’m working on a post about my personal journey with my little Luca so you can read our first-hand experience.

If you’re a regular reader and here to learn, please share this knowledge with other cat parents so they can be familiar with this terrible disease. Use these links to share with one click and help educate others: Twitter, Facebook, and Pinterest.

If you are reading this after receiving a diagnosis, know that there is a community standing by to support you.

Okay, let’s dig in.

What is FIP?

At its core, Feline Infectious Peritonitis or FIP is a disease caused by the mutation of the common, highly contagious feline enteric coronavirus (FECV). Before we dig into FIP, it’s helpful to understand how the virus that can cause this disease is transmitted.

Feline Enteric Coronavirus

FECV is an omnipresent virus that lives in the digestive tract of an infected cat and is shed through their feces. The virus is commonly passed to other cats through shared litter boxes and communal grooming.

Some cats with FECV will manage to clear the infection but are still at risk of becoming reinfected, while others will continue to carry the virus indefinitely and will continue to shed FECV in their stool.

Once infected, FECV usually presents as mild diarrhea, but an infected feline may also have vomiting or show signs of a respiratory infection. The good news is, most FECV infected cats will overcome their symptoms without any veterinary intervention.

It’s estimated that up to 90% of multi-cat households have been exposed to FECV.

You might be asking yourself, if there are so many FECV infections, and FIP comes from these infections, why have I never heard of it? The fact is most cats infected with FECV will never go on to develop the life-threatening disease known as FIP.

“In approximately 10 percent of cats infected with FeCV, one or more mutations of the virus can alter its biological behavior, resulting in white blood cells becoming infected with virus and spreading it throughout the cat’s body. When this occurs, the virus is referred to as the FIPV.” – Cornell College of Veterinary Medicine

In the illustration below, you can see that while many cats can be infected with FECV, only a portion of those will go on to have the virus mutate into FIPV, and even then, only a portion of those cats will develop FIP. Cats and kittens that remain carriers of FECV will go on to infect other cats.

FECV to FIP Mutation in Cats

If the cat is unable to clear the FIP virus (FIPV), it begins to infect their white blood cells leading to the disease known as FIP. Left untreated there is no chance of recovery.

History of FIP

While FIP may not be commonly known, that doesn’t mean it’s new. Jean Holzworth, DVM was one of the first to document the disease in 1963.

Even with decades of research, FIP remained an incurable disease. Diagnosis was a death sentence.

And while there is still an enormous number of questions left to answer, much of what we do know about FIP is thanks to the dedication of Dr. Niels Peterson and his life-long affinity to understand the disease.

Among other advances, Dr. Pedersen was the first to use an existing antiviral medication to successfully treat cats with FIP. His findings, published in 2018, gave hope to those with FIP infected cats.

Dr. Pedersen continues his research today along with his colleagues at UC Davis and researchers at other universities are taking up their own investigations.

There are currently two FIP clinical trials available to join.

For a complete history on FIP (1963 – 2022), check out this comprehensive review put together by UC Davis.

What are the Symptoms of FIP?

Here’s the most frustrating part of this disease, the symptoms can overlap with a bunch of other conditions, so it’s difficult to identify.

There are two main types of FIP wet (effusive) and dry (non-effusive), each with some more hallmark symptoms. There is also what can be considered a third form of FIP, which is a combination of the two. It’s also worth noting that one type can morph into the other.

Common Symptoms Of Both Wet and Dry FIP

While there are some symptoms that are more common to the specific type of FIP, there are five common symptoms that are seen across both.

These symptoms include:

  • Lethargy
  • Decreased appetite
  • Enlarged lymph nodes
  • Weight Loss
  • Fever
  • Unkempt coat


If you search the web for “wet FIP” you’re going to find cats and kittens with enormous bellies full of fluid. It’s quite dramatic, but wet FIP won’t always show up in such an obvious fashion.

Fluid accumulates over time and collects in the abdomen or chest. Fluid in the chest is unlikely to be visible to the naked eye.

Common symptoms of wet FIP include:

  • Anemia
  • Jaundice
  • Ascites - An enlarged abdomen filled with fluid
  • Difficulty breathing
  • Hyperglobulinemia and hypoalbuminemia


As the name implies, dry FIP doesn’t have the excess fluid surrounding the organs. The symptoms can often be vague and tend to progress less rapidly than wet FIP.

Symptoms of dry FIP include:

  • Anemia
  • Diarrhea
  • Granulomas in organs
  • Hyperglobulinemia and hypoalbuminemia
  • Neurological issues including, the inability or reluctance to jump, lameness, balance issues, poor litter box use, and seizures
  • Eye issues including, uveitis, changes to the color of the iris, cloudiness, and/or blood in the eye

FIP Risk Factors

Since FIP mutates from the feline enteric coronavirus, multi-cat households, shelters, and catteries are all breeding grounds for FECV to spread. You can interpret this to mean your cat has likely already been exposed to FECV but is unlikely to develop FIP.

Several studies have shown a several risk factors for developing FIP.


A study in Australia that was published in 2012 found that of the 382 cases of confirmed FIP, 80% occurred in cats under the age of 2 years, and 50% of the cases were in kittens under the age of 7 months.

A 2014 study showed kittens older than 6 months showed an increased resistance to FIP. This is good news for if you have an adult cat.

All of this is to say, if you bring a new kitten into your home, it’s an important time to monitor their growth and development. While FIP can occur at any age, kittens are particularly susceptible.


Several studies have shown that pure bred cats are more susceptible to FIP. And certain breeds have a higher incidence than others.

“Abyssinians, Bengals, Birmans, Himalayans, Ragdolls and Rexes had a significantly higher risk” – Journal of Feline Medicine and Surgery

If you decide to purchase one of these kittens, use a reputable breeder, and ask if they’ve had any cases of FIP in their kittens. If they say their queen has produced kittens that later went on to develop FIP, err on the side of caution and seek another breeder.


The same study found that there was no significant difference in the number of female versus male cats with FIP, but of these cats a significant number had not been neutered/spade.

This finding isn’t surprising given FIP is most commonly found in young kittens and it’s common practice to spay/neuter around 6 months of age.


There is some belief that there may also be a genetic component that may make a kitty more susceptible to developing FIP.

“It is still unknown which exact genes harbor the mutation(s) leading to FIPV development.” - Diagnosis of Feline Infectious Peritonitis: A Review of the Current Literature

How is FIP Diagnosed?

Sadly, in most cases there is no one test that can definitively say your cat has FIP, but there are some tests that point to the disease.

Physical Examination & History

Armed with the symptoms you’ve been seeing at home, head to your vet for a physical exam. Your vet will perform an overall check looking for things such as enlarged lymph nodes, swelling in the belly, fever, neurological issues, eye changes, etc.


Your vet will likely want to start with some basic bloodwork to check for abnormal values including, but not limited to high serum proteins and anemia.

They can also use a blood sample to rule out FeLV, FIV, and toxoplasmosis, which can have symptom overlap with FIP.

Your vet may also want to perform an ultrasound to check for fluid in the belly or chest. This is a hallmark symptom of wet FIP. If fluid is found your vet will recommend aspiration to take a small sample of the fluid.

NOTE: If your cat has fluid in the belly, DO NOT let your vet fully drain the fluid if you’re considering treatment. If there is too much pressure, ask your vet to remove no more 25% of the fluid. Fluid in the chest should be completely drained.

Diagnosis is often a case of elimination and looking at your kitty’s symptoms and lab values as a whole. Your doctor may not be comfortable giving you a definitive diagnosis of FIP and depending on their experience, they may have trouble recognizing the disease.

What are the Treatment Options for FIP?

As of the end of 2023, there is still no FDA approved treatment option for FIP in cats, so vets will typically offer palliative care options or euthanasia.

There is a light in all this darkness thanks to Dr. Pedersen’s research, but let’s start with how your vet can help.

Palliative Care

In the event you’re not familiar with the term, palliative care is treatment that’s used to help alleviate symptoms of a disease, and it’s used most often in cases where a disease has no cure. The goal is to make the patient as comfortable as possible in the time they have left.

The only tools your vet has in their arsenal are anti-inflammatory medications and immunosuppressants. In combination these drugs may help to prolong your kitty’s life.

If your cat has wet FIP, your vet can also drain the fluid to allow your kitty to be more comfortable, however with the underlying disease remaining, the fluid will return.

In cases where a cat has severe anemia, a blood transfusion may be recommended.

While the above medications and procedures can help alleviate symptoms and may give your kitty a boost making them appear to be on the mend, the sad fact is the meds are doing nothing to address the underlying disease.

Palliative treatments will not save your kitty.

Anti-viral Treatment

A study conducted by Dr. Pedersen and colleagues at UC Davis (published in 2018) showed there was hope in GS-441524:

“In an experimental FIPV infection of cats, GS-441524 treatment caused a rapid reversal of disease signs and return to normality with as little as two weeks of treatment in 10/10 cats and with no apparent toxicity.”

With such promising results from the 2018 study, additional research was performed using GS-441524 and similar molecules to treat FIP in cats.

One such study published in 2021 showed a cure rate of 90% when using GS-441524 to treat FIP. Amazing right?!

Sadly, unless you live in the UK or Australia, your vet will not have access to this life-saving drug. GS-441524 metabolizes to Remdesivir (GS-5734) in the body.

Does the name Remdesivir sound familiar? It’s the drug that is provisionally approved to treat COVID-19 infections in humans.

Here’s the problem, the owner of the medicines, Gilead Sciences, doesn't seem to be onboard with allowing GS-441524 for veterinary use… at least not in the US.

“The fear was that performing the studies to secure FDA approval for GS-441524 in cats might hamper efforts to approve GS-5734 (now remdesivir) in humans because if studies using GS-441524 to treat cats had any adverse effects or undesirable results, this could influence the analysis of remdesivir for human use.” – American Animal Hospital Association

So how do we get access to this life saving drug?

A group of volunteers looking to help save lives by connecting devastated pet parents with the medication they so desperately need.

How Do I Get Started with FIP Treatment?

First and foremost, always discuss any options with your vet. To get started with GS treatment, visit the FIP Warriors® website or facebook group. There are volunteers working around the clock to connect you with the resources you’ll need to treat your kitty.

I spoke with Robin Kintz, the founder of FIP Warriors®, and here's a message of hope she shared for all cat parents with newly diagnosed FIP cats and kittens:

“FIP is no longer a death sentence! With proper guidance and supportive veterinary care, 90% of FIP kitties can now be cured!” - Robin Kintz

You’ll get an estimate up front on what the cost will be for treatment, and you can buy the medication as you go, allowing you to spread the cost out over the course of treatment.

The FIP Warriors® will connect you with a pet parent in your area that is treating their own kitty that will supply started meds and supplies.

Full disclosure, other than the wonderful and caring life-saving work FIP Warriors® did for my Luca, I have no business relationship with or financial incentive to recommend this group.

What Can I Expect During GS Treatment for FIP?

There are two distinct phases of FIP treatment, on average each lasting 84 days. You’ll be assigned an FIP Warriors® administrator that will guide you through the process from start to finish.

Your administrator will be a wealth of information having treated many FIP cats of their own and supported hundreds of pet parents through the years.

FIP Treatment Phases

The first 84 days of treatment is when you administer the GS medication. Many pet parents will start with an injectable medication and will continue with injections for all 84 days.

The dosage and brand are determined by the type of FIP, and the dose will increase as your kitty gains weight.

Injections are typically recommended to start because they are better absorbed through the subcutaneous injection rather than relying on the digestive tract, which may be compromised by the disease.

Some pet parents will be given the option to switch to pills further into treatment. Treatment with pills is more expensive, but typically much easier to administer.

Labs are typically recommended every 4 weeks during treatment to track progress.

Depending on the severity of the disease and how your kitty is responding to treatment, you may need to extend treatment past the minimum 84 days.

What you need to know for treating your cat at home.

A pet parent with a geriatric cat may have more experience and be better prepared for the requirements of at home treatment. This includes weighing your kitty, taking their temperature, giving them pills and injections, and in some cases subcutaneous fluids.

Every kitty is different and additional medications may be needed to support their recovery. It’s important to have a vet that will provide supportive care should you decide to begin treatment. While they won’t be able to advise you on the GS medication, they can provide supportive care for other symptoms your kitty is experiencing.

The GS medication itself is viscous, think pushing honey vs water through a syringe. It’s also very acidic, making it quite painful for many kitties to receive and if the medication leaks onto their skin it can result in sores.

While many parents do treatment alone, it tends to be much easier when you have an extra set of hands, one person to hold your kitty, one person to inject.

Treatment can be emotionally draining and there will be good days and bad. What helps parents continue with the process is the improvement they see in their kitty and the support they receive from other parents in the same situation.

If you’re familiar with the Kitten Lady, Hannah Shaw, she treated her cat Coco for FIP, and Coco is now cured! Check out this video where she talks about her experience:

FIP Observation Phase

This milestone begins when you’ve been given the green light to stop administering the GS medication.

During this period, you’ll watch your kitty to ensure none of their original symptoms return. You’ll monitor their weight, their activity level, their appetite, etc.

You’ll also have bloodwork checkpoints during the observation period.

If your kitty backslides and begins to show symptoms, you’ll begin treating with the GS medication again, oftentimes at a higher dosage. If the observation period is uneventful, your kitty will be considered cured.

Coping with an FIP Diagnosis

You may have left your vet’s office being told your kitty has a terminal illness and euthanasia is your only option. Or perhaps your vet puts their veterinary license at risk by telling you about a treatment plan that you’ll have to pursue on your own. Either way, you’re leaving their office gutted and scared for your fur baby. I get it.

Maybe you are like me, waiting for additional labs to come back desperately hoping there is some other cause of your cat’s symptoms, but still diving into FIP research to understand what the diagnosis might really mean.

One thing I can confidently tell you is the FIP Warriors® are a community that will support you whether you decide to try treatment or not. They will answer all of your questions, encourage you when you are down, and will share their vast experience to help you through the process.

FIP Frequently Asked Questions

No, FIP is not contagious. There is often confusion around this topic because the virus (FECV) that has the potential to mutate into the FIP virus is highly contagious.

No. Odds are your other kitties have already been infected with FECV, but that does not mean they will go on to develop FIP.

Yes, it is. On a positive note, many cat parents create fundraisers to help with the cost, and in a community facing the same fight, small donations add up to make a significant difference.

Contact FIP Warriors® at https://fipwarriors.com/ or on their facebook page to connect with volunteers that will connect you with the resources you’ll need for treatment.

Sadly, there are people in this world that are looking to take advantage of others. These people often try to pass off fake medications or use medications from sellers that are not reputable. Ensuring your kitty gets enough medication is imperative to their success. The FIP Warriors® do batch testing to ensure the brands they use are of the highest quality available. Do not trust anyone that guarantees a cure. While GS treatment has a high success rate, it does not cure every cat.

sockFIP.org is a non-profit organization that consolidates a wealth of research information related to FIP. You can learn more about research that is taking place globally to better understand this horrible disease.

Have you ever had a cat or kitten diagnosed with FIP? If so, what type, wet/dry? What treatment method(s) if any did you try? Share the story of your warrior in the comments below. While we love stories with happy outcomes, we also know that’s not the ending to every story. Don’t let that stop you from honoring your warrior.

K Marie Alto
K Marie Alto

K. Marie is an animal lover, wife, kitty mom, dog auntie, writer, and co-founder of Toe Beans, a proud American family-owned online boutique pet supplies store focused on the improvement of the life of furry family members via pet parent education, better products, and advocacy. She has over 20 years of experience as a pet momma. She loves sharing her personal journey and experience as a pet parent via her blog and Facebook page where she currently has more than 50K followers (@furrytoebeans) and counting :-). Read more

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