FIP or Feline Infectious Peritonitis: THE DIAGNOSIS THAT USED TO BE A DEATH SENTENCE

If you've spent any time around cats, you may have heard the letters FIP and immediately thought, Oh no.

For a long time, that reaction would have been understandable. Feline Infectious Peritonitis was considered a devastating disease, and once a cat developed clinical FIP, it was generally considered fatal without treatment.

But things have changed.

And two young cats currently being fostered through Fresno TNR are proof of just how much has changed.

Meet Holler and Shilo.

Both are juvenile cats who developed FIP. Both became seriously ill. And both are now doing incredibly well on oral FIP medication.

In fact, if you watched the two of them playing, wrestling, snuggling and acting like completely normal young cats, you would never guess what they have been through.

SO, WHAT EXACTLY IS FIP?

FIP stands for Feline Infectious Peritonitis, and it is caused by certain forms of feline coronavirus.

This part can get a little confusing because feline coronavirus is actually very common in cats, especially where cats live in groups.

Most cats that encounter feline coronavirus never develop FIP. The virus usually lives in the gastrointestinal tract and causes little or no illness. Some cats may have mild diarrhea or mild respiratory symptoms and recover on their own.

In a small percentage of infected cats, however, the virus undergoes mutations that change its behavior. The mutated virus can infect white blood cells and travel throughout the body. The cat's immune response to that infection can then cause the severe inflammation associated with FIP.

According to the Cornell University College of Veterinary Medicine's Feline Health Center, only a small percentage of cats exposed to feline coronavirus go on to develop FIP.

And that is when things can become very serious.

THERE ARE TWO FORMS OF FIP

FIP generally appears in two forms: wet FIP and dry FIP.

Wet FIP is called the effusive form. In these cats, fluid can build up in the abdomen or chest. A cat may develop a swollen or "pot-bellied" appearance, and if enough fluid accumulates in the chest, breathing can become difficult.

Dry FIP is called the noneffusive form. This form can affect organs throughout the body and may cause neurological problems when the central nervous system is involved. Signs can include seizures, difficulty walking and poor coordination.

And just to make things more complicated, FIP doesn't always stay neatly in one category. A cat can progress from one form to the other.

WHAT DOES FIP LOOK LIKE?

The early signs can be frustratingly nonspecific.

A cat with FIP may stop eating, lose weight, become depressed or lethargic, and develop a fever. Depending on the form of FIP, other symptoms can develop as the disease progresses.

That is one reason FIP can be so difficult to diagnose.

There isn't currently one simple test that can say, Yes, this cat definitely has FIP.

Coronavirus antibody tests can't distinguish between ordinary feline coronavirus exposure and FIP. Other tests, including PCR and tests that look for viral proteins, can provide useful information, but none is 100 percent accurate.

Veterinarians therefore look at the whole picture — the cat's history, physical examination, symptoms and laboratory results — when making a presumptive diagnosis.

AND THEN THERE IS THE GOOD NEWS

This is the part I really want people to know.

FIP is treatable.

Not that long ago, FIP was considered essentially untreatable and almost always fatal. Today, antiviral treatment has completely changed the outlook for many cats.

One of the most extensively studied medications is GS-441524. According to the Cornell University College of Veterinary Medicine's Feline Health Center, studies in laboratory cats and naturally occurring cases have found GS-441524 to be a safe and effective treatment option. An oral compounded formulation is now available in the United States through a veterinary prescription.

That brings us back to Holler and Shilo.

MEET HOLLER

Holler is an adorable gray juvenile cat who came to Fresno TNR after one of our wonderful volunteers, Theresa, saw a post on Nextdoor.

The post suggested that a cat had possibly been hit by a car.

Theresa went to check on him, and Holler ended up coming into Fresno TNR's care.

As his condition was evaluated, it became clear that something much more complicated was going on.

Brandi suspected Holler was suffering from FIP.

Today, Holler is receiving oral FIP medication — and the difference is incredible.

He plays.

He wrestles.

He snuggles.

He acts like a young cat who has absolutely no idea that he was once facing a very serious disease.

And when he finishes his medication, he will be looking for his forever home.

THEN THERE'S SHILO

Shilo is a beautiful dilute calico who came to Fresno TNR through one of our Facebook followers.

Her story was especially scary.

She had developed neurological symptoms and had reached the point where she couldn't stand at all and was having seizures.

Imagine looking at a young cat who can't even stand and wondering what could possibly be done. Once again Brandi, with her innate sense of diagnosing cats, suspected FIP.

Shilo started on oral FIP medication and the transformation happened over a couple of weeks from not being able to stand at all to using her back legs, albeit wobbly.

And now?

You would never know.

Shilo plays. She wrestles with Holler. She snuggles. She acts like a normal, happy young cat.

The same kitten who couldn't stand is now running around and doing what young cats are supposed to do.

And once she completes her medication, she will also be ready for adoption.

FIP IS STILL SERIOUS — BUT THERE IS HOPE

It's important not to minimize FIP. It is a serious disease, and treatment can be complicated. The Cornell Feline Health Center notes there are still questions surrounding antiviral therapy, including long-term effectiveness, ideal dosing and the possibility of drug resistance.

There is another part of FIP treatment that isn't always talked about: the medication can be very expensive. GS-441524 has to be specially compounded, and the cost can add up quickly. But when you watch a kitten like Shilo go from being unable to stand to running around, wrestling and snuggling with her foster brother, you realize just how worthwhile that treatment is. The generous donations we receive through Fresno TNR help make it possible for us to say, “Yes, let's give this cat a chance.”

The word FIP no longer has to mean there is nothing you can do.

That is a huge change.

And Holler and Shilo are two very good reminders of that.

CAN I CATCH FIP FROM MY CAT?

No.

According to the Cornell University College of Veterinary Medicine's Feline Health Center, coronaviruses are not known to be transmissible from infected cats to humans.

Another important point is feline coronavirus can spread between cats, but FIP itself is not believed to spread from cat to cat in the same way. FIP is believed to develop when feline coronavirus infection mutates within an individual cat.

WHAT ABOUT THE OTHER CATS IN MY HOUSE?

Because feline coronavirus is common and can spread between cats, good hygiene and good cat husbandry are important.

Keep litter boxes clean and away from food and water dishes, and avoid overcrowding whenever possible. The Cornell Feline Health Center also notes keeping cats healthy and appropriately vaccinated against other illnesses may help decrease the likelihood of FIP developing.

If your cat is showing symptoms that concern you, or if you suspect FIP, talk to your veterinarian. FIP can be difficult to diagnose, and every cat is different. Your veterinarian can evaluate your cat's individual symptoms and medical history and discuss appropriate testing and treatment options.

A LITTLE HOPE GOES A LONG WAY

FIP used to be one of those diagnoses that made everyone involved feel helpless.

Today, we have something we didn't have before:

Hope.

Holler and Shilo aren't statistics to us. They're two cats who got very sick and were given a chance.

And now they're thriving.

Holler and Shilo are both still on their medication, but their futures look very different than they once did.

Soon, they'll finish treatment, find their forever homes and hopefully spend the rest of their lives doing what every young cat should be doing:

Playing, wrestling, snuggling and getting into a little bit of trouble.

And honestly, we're perfectly okay with that.

A NOTE ABOUT FIP

The information in this article is intended for general education and is not a substitute for veterinary advice. If you are concerned that your cat may have FIP, please consult your veterinarian. Diagnosis and treatment decisions should be made with a veterinary professional who can evaluate your individual cat.

Source: Cornell University College of Veterinary Medicine, Cornell Feline Health Center, Feline Infectious Peritonitis (FIP), updated 2024.