Feline FIP:
Understanding a Deadly Cat Virus

I painfully learned about Feline FIP, feline infectious peritonitis, long before I became a veterinarian. In fact, this virus in cats is a major reason that I ended up becoming a feline veterinarian. I had never even heard of FIP the day my kitten suddenly had hazy eyes. All I knew was that something was very wrong with my kitty's ordinarily gorgeous cat eyes. They appeared very cloudy inside, and it didn't take long for me to realize that he couldn't see.

Despite having been in contact with my kitten's regular veterinarian, as I will explain more later, my gut told me I needed to do more right away. Very late that night, my husband and I jumped into our car and began a 2 1/2 hour drive to New York City, my precious scared kitty clinging to me all the way.

When we arrived, after a lot of tests and differential discussions, I received the devastating news: Noodles had feline FIP. At the time, I had no idea what that meant, except that his veterinarian was telling me he would die.

What is Feline FIP?

Feline FIP is a heartbreaking illness that primarily afflicts kittens, and is almost always fatal. It occurs due to a mutation of one particular strand of the feline coronavirus (FCoV), of which there are many strands that many cats are exposed to throughout their lifetimes and especially as young kittens. Usually, there are 2 primary factors that contribute to the likelihood that a cat will develop FIP.  The first factor is that the cat comes from a multicat environment, such as a shelter or a breeding facility. The second is that the cat has suffered some recent stress, such as moving to a new household or being neutered.

That said, however, not all cats will develop FIP even if they have had these two primary factors. Not only does the cat have to have been exposed to one particular strand out of hundreds of FCoV strands, but he also has to have what is believed to be some sort of genetic predisposition to cause the strand to mutate. For example, an entire litter of kittens from a cattery would be exposed to the feline enteric coronavirus strand yet only one kitten will develop cat FIP. I personally had this happen with one of my clients recently. He purchased two kittens from the same cattery, although they came from different litters, and both tested positive for the corona virus (more on this testing later). It is safe to assume that both kittens were exposed to the same strand, since they were born and raised in the same environment, but only one developed and ultimately died of feline FIP.

Unfortunately, there are many aspects of feline infectious peritonitis that we still don't fully understand, making it difficult to explain risk factors, to diagnose, and to treat. What we do know is that feline FIP often affects young, innocent kittens and takes their lives.

Symptoms of Cat FIP

gray and white cat with feline fip
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In my personal experience, I didn't know what could be responsible for the change in my kitten's vision. Just the day before, my kitten was playing with his kitten toys, eating his kitten food and acting, in every way, like a perfectly normal kitten. He had, however, just been seen by the local veterinarian for mild cat conjunctivitis and a mild feline upper respiratory infection for which I was giving him antibiotics by mouth and cat antibiotic eye drops.

The symptoms of FIP in cats were totally unknown to me. All I knew was that I was very frightened when I realized he couldn't see, so I called the veterinarian right away. Unfortunately, my veterinarian, whom I had great faith in, said to just continue the cat medication and that was all we could do. He didn't even want to re-examine my kitten again. I was in some sense relieved, and yet, I couldn't shake the feeling that there was something more serious going on. Never did I imagine that the serious mystery condition was one that would likely prove fatal for Noodles.

There are two types of feline FIP, which can have very different symptoms. The two forms are a wet (effusive) and a dry (noneffusive) type. Furthermore, unfortunately, the symptoms can be quite vague and can indicate a number of other cat health problems as well.

Cats with the noneffusive type of FIP may have weight loss, lethargy, fever, a poor hair coat, and anemia, but will not accumulate fluid in the abdomen or chest.

The wet, or effusive, type of FIP in cats can share the same symptoms as the dry form, such as fever, loss of appetite, weight loss, and lethargy, but is primarily identified by the collection of fluid in the abdomen and occasionally the chest. The amount of fluid may increase quickly and make it difficult for the cat to breathe.

I found out that the cloudy appearance in my kitten's eyes was caused by a condition called anterior uveitis, or inflammation in the front chamber of the eye. This condition is one of the symptoms that you may see with fip in cats. It appeared that my kitten, Noodles, had the dry form of feline FIP in cats which was causing the inflammation in his eyes, along with his fever and his decreased appetite and lethargy.

Diagnosis of Feline FIP

The night I knew there was something seriously wrong with Noodles, we headed to the Animal Medical Center in Manhattan, a truly amazing place. At the time, I had never seen or imagined anything like it. It looked just like a hospital for people, but was for animals. It was there that I learned that the possible causes of my kitten's eye problems were Feline Infectious Peritonitis, Feline Leukemia, or Toxoplasmosis. FIP is a diagnosis that is made by ruling out these other conditions, among others, because there is no single test for feline infectious peritonitis.

FIP tests are unreliable in providing a definite diagnosis. FIP is diagnosed based on a variety of findings that help piece together parts of a puzzle. There is no single, definitive test for FIP except via a brain biopsy after the cat has died of FIP. On rare occasions, it can be diagnosed by an intestinal biopsy, but finding a positive result via this method is more hit-or-miss.

In most cases, we assemble pieces of a puzzle. The first two factors are those discussed earlier: the cat must have a history of coming from a multi-cat environment and have had a recent stress like surgery, moving to a new home or being introduced to other cats, or even a recent vaccination. Secondly, the cat often has weight loss or a failure to grow and a persistent fever for more than 4 days.

If your veterinarian suspects that your cat has feline FIP, tests include bloodwork including a full chemistry panel and CBC, testing for FeLV, FIV, and toxoplasmosis, and running a FCoV titer. Your veterinarian will be looking for a number of factors in your cat's chemistry and CBC panels, including anemia, low white cells, and abnormal enzyme levels. A cat with FIP will also have a high FCoV titer.

It should be noted that a high FCoV titer ALONE is not enough to support the diagnosis of feline FIP. As discussed earlier, there are many different strands of FCoV, and this test cannot differentiate between strands. All it tells you is whether a cat has been exposed to a coronavirus, not to whether she has been exposed to the feline enteric coronavirus AND not whether that strand had mutated into FIP into a given cat. If all of these factors are not present, but some are, there are additional specialized laboratory tests that can be conducted, including an alpha-1 glycoprotein test and protein electrophoresis. I highly recommend that any suspicion of FIP be further investigated with these tests.

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Cats with the effusive form of FIP can also have fluid drained from their abdomen or chest for analysis at a lab. Additionally, there is a test called the Rivalta test that can be conducted on the fluid sample if your veterinarian is willing to do so, although the test itself is considered non-scientific. For more information about this test, please see this website (opens in a new window).

The diagnosis of FIP is regrettably quite complicated, and it is important to request many, if not all, of these tests from your veterinarian. Unfortunately, feline infectious peritonitis is often misdiagnosed, and I have heard of far too many cases where a young cat with a fever has been given this death sentence with NO other indications of having FIP. If your vet is not familiar with these protocols, I highly recommend visiting Dr. Addie's site, the world's expert in FIP from Glasglow, where you can provide your vet with a flowchart for diagnosis and even worksheets to help support your cat's diagnosis.

Noodles was tested for all of the above, was negative for toxoplasmosis and leukemia, but the results of the feline FIP tests indicated he was positive. I was advised to euthanize my little kitten. I was told I needed to euthanize him so that he wouldn't be around my other cats and infect them. At the time, FIP in cats was thought to be highly contagious. Now, however, we understand that the virus needs to be shed in a cat's stool, ingested by feces to mouth of another cat, and then mutate within the new cat's body -- a process that doesn't make it as contagious as initially believed. That said, isolating a cat with FIP from other cats, especially the very young or very old, is still advised.

FIP Treatment

gray and white cat with feline fip
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When I received the diagnosis for Noodles, I refused to believe that my only option was to euthanize him, so I read everything I could get my hands on about cat FIP, and even started calling veterinary schools around the country in an attempt to find out anything I could about fip treatment. I was desperate to find someone who would tell me how to save my kitten's life.

One of the veterinary schools I called, the College of Veterinary Medicine at Cornell University, was exceptionally helpful and I suddenly found myself talking to Dr. Johnny Hoskins, whom I have since come to know as one of the feline FIP experts of the world. I was so fortunate that a busy Cornell Professor with students to supervise, classes to teach, journal articles to write, lectures and traveling to do would get on the phone with me, a nobody in the world of veterinary medicine at the time, to talk about my kitten and Feline FIP.

In a nutshell, Dr. Hoskins confirmed that almost all cats with FIP die quickly, but also assured me that my other cats had already been exposed, so euthanizing Noodles to save them would not be the reason to do so. While it was a long shot, he let me know that there was feline infectious peritonitis treatment I could try. A handful of cats had survived FIP and I was determined to give my kitten, Noodles, the best chance possible to become one of those cats.

The standard protocol for treating cats with FIP is to give steroids by mouth and antibiotics to help control fever and/or prevent infections that can result from immunosuppressing a cat. In Noodles's case, because of his eye involvement, I also needed to give him steroid drops in his eyes. On my own conviction at the time, I also started Noodles on a Vitamin C powder supplement formulated for cats with viral diseases.

Since that time, additional treatments have emerged as ways of helping to prolong the lifespan of infected cats. Among those treatment options are feline interferon omega (Virbagen) or less ideally human interferon alpha. Both of these medications have shown some success in curing or at least significantly prolonging the lifespan of cats with non-effusive FIP. Unfortunately, most treatments available today seem to have little affect on the effusive or wet FIP cases.

Cats with FIP today are also often placed on a variety of vitamin supplements, including Vitamins A, B1, C, and E, as well as a B-complex vitamin.

Prognosis and Outcomes

For several months, Noodles received his steroids and Vitamin C and chicken baby food, which was all he would eat. FIP in cats causes a decrease in appetite so it was difficult to get him to eat. He was quiet, not playful like a kitten should be, but he ate, slept, cuddled and seemed content. Miraculously, over the next months, he slowly improved, his eyes cleared up completely and he had perfect vision and he began to play and eat better.

15 years later, Noodles had to be euthanized from an entirely unrelated condition, after living 15 glorious years as my best feline friend ever. There are those who will say he probably never had Feline FIP or he wouldn’t have lived. However, I feel strongly that he did especially after going on to Veterinary School myself and practicing for over 20 years now in my own feline only hospital. I have learned even more about FIP in cats and have had numerous patients with the disease.

Since Noodles, I have diagnosed and treated and, unfortunately, euthanized many cats with Feline FIP. I have attended numerous seminars on FIP in cats and read every new bit of information that comes along. I have consulted further with the cat FIP experts of the world, including Dr. Hoskins, who saved Noodle’s life by giving me hope and suggesting and encouraging treatment when no one else would.

Several years later, when I had become a feline veterinarian, Dr Hoskins again guided me through another FIP case that went on to live to the ripe old age of 18. That cat had all the signs of FIP as well as all the positive test results AND had an intestinal biopsy that confirmed the presence of the FIP-type lesion in the tissue. He was also treated with prednisolone and slowly recovered.

That said, it is still quite rare for cats to recover from FIP. However, there are reports of more and more cats who have done so. Most survival stories are for those cats with the dry form of the disease, but there are some indications that cats with even the wet form can overcome it. We have a long way to go before we have a cure, or even better treatments, but we are slowly moving forward.

You can hear more about research progress regarding FIP in cats in our radio show discussion with Steve Dale:

Most recently, I have worked with another cat with effusive FIP. He was treated oral prednisolone, the recommended vitamins, antibiotics, and Feline Interferon. The feline interferon is very expensive and had to be imported from Great Britain, but this kitty's loving owner was determined to do everything possible to save his cat's life. While he did exceed the length of time I originally thought he would live, and the length of time any cat with effusive FIP is expected to live, he was still, sadly, one of the many victims of FIP.

Additional Resources

The following resources and discussions may prove helpful in your search for information about feline FIP:

You may also read the questions and answers below from readers who have had experiences with cat FIP.

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