FIP In Cats Today: From a Once-Fatal Diagnosis to a Treatable Disease

Not long ago, a diagnosis of Feline Infectious Peritonitis (FIP) felt like the end of the road. Because it effectively was. Owners were often told there were no options, no treatments, and no realistic hope. It once was akin to a death sentence for our beloved feline friends.

That reputation has been slow to fade but the reality has changed dramatically.

In 2025, FIP is no longer an automatic death sentence. It is still serious. It still requires urgency. But it is now a treatable disease, and many cats go on to live completely normal lives after therapy.

Understanding what FIP is — and what it isn’t — matters more than ever.

What FIP actually is

FIP begins with something extremely common: feline coronavirus. This is not the same thing as COVID-19, and it is not rare or exotic. In fact, studies show that almost all cats who have ever lived in a multi-cat environment; shelters, breeding catteries, foster homes, or multi-cat households have been exposed to feline coronavirus at some point in their lives.

For the vast majority of cats, that’s where the story ends. It's more common than a cold....

In a small percentage of cats, however, the virus mutates inside the individual cat. When that mutation triggers an abnormal immune response, FIP develops.

That’s why you’ll hear FIP discussed in “types”:

• Effusive (“wet”) FIP (fluid build-up typically in the abdomen)

• Non-effusive (“dry”) FIP

• Ocular and/or neurological FIP (eyes/brain involvement)

  
  

The important point isn’t the label—it’s that FIP is treatable now, even in many complex cases, especially when therapy starts quickly.

Importantly, less than 5% of cats exposed to feline coronavirus will ever go on to develop FIP.

That distinction matters because it explains why FIP can feel so random, and why it can happen even when everything else is done “right.”

What FIP is not

This is where a lot of fear and misinformation still lives.

FIP is not contagious. Feline coronavirus can spread between cats, but the mutated form that causes FIP is not considered something that passes cat-to-cat. A cat develops FIP because of what happens inside their own body, not because they “caught FIP” from another cat. Even cats that need treatment for FIP do not need to be secluded from other cats in the home.

FIP is not proof of neglect or bad breeding. FIP does not discriminate. It appears in rescue kittens and well-planned litters, in excellent breeders and terrible ones, in shelters and even single-cat homes. It is not a reflection of love, effort, ethics, or care. It is a combination of biology, immune response, and chance.

Genetics may play a role, but they are not pre-determined destiny. There is evidence that some cats may have a genetic susceptibility that makes mutation more likely, I've heard of multiple cases of sibling cats getting FIP in their life, but this is not a simple inheritance pattern. A cat can also come from lines with no prior cases and still develop FIP, while many related cats may never be affected. It is risk, not inevitability.

Why FIP in Cats used to be considered fatal

For decades, there simply weren’t treatment options that had been invented/created/studied yet, let alone available through veterinarians. Supportive care could ease symptoms, but it could not stop the disease process. That reality shaped how FIP was taught in vet schools and discussed in clinics and it takes time for those narratives to catch up to science.

But just a few short years ago, everything changed with antiviral therapy.

The “black market” era — and why it existed

Before veterinarians in North America could legally prescribe effective treatment, desperate owners found another way.

Online support networks including groups like FIP Global Cats, helped families access antiviral medications, navigate dosing, and support each other through treatment. These groups saved thousands of cats at a time when there was no legitimate medical alternative.

Despite the "black market" moniker, that period wasn’t reckless it was necessity. Both for the cats it saved, but also so that more research could occur. It also allowed time to get the drugs formally legalized without sacrificing all the suffering cats during a multi year period to have the drugs reviewed by the FDA and the Canadian equivalents.

At the same time, black-market medication came with real risks: the possibility of inconsistent quality, unclear sourcing, and immense stress for owners who were already terrified. Everyone involved knew this was not how medicine should work but for many thousands of cats worldwide, it was the only reason they survived.

Where we are now: legal treatment options

Today, the landscape is very different.

• In Canada, veterinarians can legally access GS-441524 through approved pathways, allowing proper prescribing, monitoring, and support.

• In the United States, veterinarians now have access to compounded GS-441524 for oral use under current regulatory guidance.

This means many cats can now be treated openly, legally, and with veterinary oversight, rather than relying on more risky underground networks.

Why some vets still aren’t aware or are hesitant

Even now, some owners are surprised to hear outdated advice. This usually isn’t malice or indifference. It’s a mix of:

• years of being taught FIP was fatal,

• rapidly changing regulations and science

• For years, there truly wasn’t a straightforward legal prescribing route, and many clinicians were (appropriately) cautious about discussing unlicensed therapies. In some areas in North America, even discussing it without being legally approved could result in the possible forfeiture of their license/ability to practice Veterinary medication.

  
  

The key takeaway is this: it is reasonable to advocate for your cat. Asking about current antiviral options or seeking a referral is not being difficult. Vets are wonderful on the whole, but no one can be expected to know everything. If a diagnosis of FIP is found and your vet isn't willing to have this conversation, PLEASE find a new vet.

Speed matters more than anything else

If there is one factor that consistently separates successful outcomes from tragic ones, it is how quickly treatment begins.

FIP can progress fast. Starting antivirals early, sometimes even before absolute diagnostic certainty, can dramatically improve survival and recovery. Waiting “to be sure” can cost valuable time.

Injections vs pills — and side effects

Treatment can involve injections, oral medication, or a combination, depending on the cat’s condition.

• Injections are sometimes used early, especially in very sick cats, but they can be painful and may cause local reactions/open sores though it is not very common.

• Oral medication is now widely used and far easier for many families to manage long-term.

Side effects do happen in some cats: gastrointestinal upset, lethargy, injection-site irritation. Which can be disturbing to witness in a cat that is already suffering, but it’s important to keep perspective. A few weeks of side effects (for the cats who experience them) is vastly preferable to guaranteed death without treatment.

Most cats tolerate treatment remarkably well, especially when supported properly.

What We Do at Our Cattery to Reduce Risk (Because Elimination Isn’t Realistic)

No breeder, shelter, or multi-cat home can promise zero risk of FIP. Anyone who says otherwise is at best misunderstanding the disease and at worst deliberately unwilling to learn. What can be done is thoughtful risk reduction, grounded in veterinary science rather than fear or marketing claims.

At our cattery, we focus on the factors that are actually within human control:

• Small, stable social groups We avoid overcrowding and unnecessary mixing. Stress and viral load are known contributors to feline coronavirus replication, so limiting density matters.

• Excellent hygiene without chasing sterility Litter boxes and shared spaces are managed carefully, with consistent cleaning practices that reduce exposure without attempting an unrealistic “virus-free” environment.

• Stress reduction during critical life stages Extra care is taken around weaning, growth periods, rehoming transitions, and social changes, all times when a kitten’s immune system can be under increased pressure.

• Close health monitoring Subtle changes in appetite, weight, or behaviour are taken seriously. Early veterinary involvement is encouraged rather than delayed.

• Conservative, data-aware breeding decisions While genetics are not destiny, trends over time are observed carefully, and transparency guides our breeding choices.

• Age-appropriate placement (16 weeks) Kittens are not rushed into new homes. Immune maturity matters, and patience is part of responsible care.

• Education and openness with kitten families We believe informed owners are safer owners. FIP is discussed accurately and calmly, with emphasis on early action rather than fear.

  
  

Our track record at PureX

In over 11 years of breeding, we have not had a single confirmed case of FIP in either our adults or our kittens. Statistically, given the prevalence of feline coronavirus in multi-cat environments, we would reasonably expect to have seen two to three cases by now.

We are careful to say this plainly: part of that is luck — because FIP can happen even when everything is done right. But we also believe it reflects that our risk-reduction practices are working as intended.

This history is not a guarantee, and it is not a promise that FIP can never occur. It is simply evidence that lower stress, lower density, thoughtful management, and early vigilance do matter.

The most important thing to remember

FIP today is not the same disease in 2025 that it was even five years ago.

It is still frightening. It is still urgent. But it is treatable, and many cats go on to live long, healthy lives after therapy.

If FIP ever touches your world, know this: It is not a reflection of failure. It is not a death sentence. And it is no longer something that must be faced without hope.

References

Cornell University College of Veterinary Medicine. (n.d.). Feline infectious peritonitis (FIP). Cornell Feline Health Center.https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/feline-infectious-peritonitis

Cornell University College of Veterinary Medicine. (2024). FIP treatment with GS-441524 now available in the United States. Cornell Feline Health Center.https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/fip-treatment-gs-441524-now-available-us

VCA Animal Hospitals. (n.d.). Feline infectious peritonitis.https://vcahospitals.com/know-your-pet/feline-infectious-peritonitis

Pedersen, N. C., Perron, M., Bannasch, M., Montgomery, E., Murakami, E., Liepnieks, M., & Liu, H. (2019). Efficacy and safety of the nucleoside analog GS-441524 for treatment of cats with naturally occurring feline infectious peritonitis. Journal of Feline Medicine and Surgery, 21(4), 271–281.https://pmc.ncbi.nlm.nih.gov/articles/PMC6435921/

Dickinson, P. J., Bannasch, M., Thomasy, S. M., Murthy, V. D., Vernau, K. M., Liepnieks, M., Montgomery, E., & Pedersen, N. C. (2020). Antiviral treatment using GS-441524 in cats with neurologic feline infectious peritonitis. Journal of Veterinary Internal Medicine, 34(4), 1587–1593.https://pmc.ncbi.nlm.nih.gov/articles/PMC7403484/

International Cat Care. (2023). Feline infectious peritonitis: An update on diagnosis and treatment.https://icatcare.org/resources/feline-infectious-peritonitis/

Government of Canada. (2024). Emergency drug release (EDR) program for veterinary drugs. Health Canada.https://www.canada.ca/en/health-canada/services/drugs-health-products/veterinary-drugs/emergency-drug-release.html

Weese, J. S. (2024). Access to FIP drugs in Canada. Worms & Germs Blog.https://www.wormsandgermsblog.com/2024/02/articles/animals/cats/fip-drug-access-canada/

U.S. Food and Drug Administration. (2024). FDA announces position on use of compounded GS-441524 to treat feline infectious peritonitis.https://www.fda.gov/animal-veterinary/cvm-updates/fda-announces-position-use-compounded-gs-441524-treat-fip

Stokes Pharmacy. (2024). GS-441524 for treatment of feline infectious peritonitis.https://www.stokespharmacy.com/fip/