Finally: Feline Infectious Peritonitis (FIP) is treatable!

Updated: Sep 16, 2020

Due to popular request -- and some exciting news -- we're going to start our blog series by talking about Feline Infectious Peritonitis (FIP).

Recently, members of the Nine Lives Foundation attended a symposium on FIP at UC Davis, and that is the source of most of the information presented here. I will also link to other sources of information at the end of this blog.

Theodore lost his life to FIP before there was an effective treatment.

This is a topic that is near and dear to many cat owners, including many of our Nine Lives community. For those who have visited our Adoption Center, you may have noticed a photo of a handsome cat near the reception desk -- that is Theodore, who was the Nine Lives "clinic cat" before being adopted. Sadly he succumbed to "wet" FIP last year.

There are few feline diseases that are scarier than FIP. For as long as it has been identified, it has been considered 100% fatal, without any way to treat or even prevent it. It snatched away mostly young cats and kittens, as well as some adult cats, often with little to no warning, leaving heartbroken owners helpless and traumatized with no options to help their beloved fur babies.

There is good news though, which is so exciting that I can't wait any longer to write it -- studies done at UC Davis have produced an amazing breakthrough: a cure for FIP! The overall consensus among experts at the recent FIP symposium was that finally FIP can be considered a treatable disease.

I am also excited to be able to say that despite the cost and the difficulty in procuring it, that Nine Lives has 8 cats currently being treated with great success so far. The treatment process is expensive however, costing from $1400-$4000 per cat, depending on their symptoms, size and rate of recovery. We need your financial support to give these cats lifesaving treatment, and we ask that you consider a donation, however small. Every dose matters!

Please consider a financial donation to help us give these cats a chance to live!

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Peanut is one of the kitties currently being treated for FIP. He is in foster care and receives his treatments at home, and his progress is regularly monitored by Dr. Rudiger. His transformation has been nothing short of amazing, as within days he went from death's door to a happy, playful, energetic kitten. Peanut will finish up his treatment at the beginning of March, but we need your support to continue his treatment, and to treat more cats and kittens like him.

What is FIP anyway?

So with all that exciting news out of the way let's back up and talk about FIP. FIP is a relatively new virus on the scene, which seems to have arrived on the scene only about 50 years ago. Before we can talk about FIP though, first we have to talk about FECV - Feline Enteric Coronavirus.

FIP starts out as FECV. FECV is a feline coronavirus, which is seemingly both innocuous and ubiquitous -- most of the time. It is spread through fecal-oral transmission, and while incidence of it is low in outdoor cat populations, it is estimated that as many as 90% of cats from multi-cat households, catteries, or shelters carry the virus. Since it usually produces little to no symptoms, there is rarely any indication that it is present, and it usually does not cause any problem for the cat.

In a small number of cats however, FECV mutates and may become the deadly FIPV virus. (There are actually two strains of FIPV: FCoV-1 which accounts for 85% of FIP cases, and FCoV-2 which accounts for the rest.) The virus usually replicates in intestinal epithelial cells, and can cause some mild symptoms such as diarrhea or other gastrointestinal distress. Sometimes however, the virus mutates in such a way that it is picked up by macrophages -- a type of white blood cell -- which then allows it to circulate and affect other parts of the body. This is when it becomes FIP.

Because the virus is able to subvert the immune system via the macrophages, it makes it very difficult for an cat to fight off the virus. In fact, it re-programs the infected cells in such a way that they bypass programmed cell death (apoptosis) which is one of the body's ways of limiting the spread of a virus by getting rid of infected cells. This results in zombie cells which continue churning out more copies of the virus.


Luckily however, FIP itself is not directly contagious. The virus is mostly confined to internal lesions and effusions, meaning that FIP is not (naturally) spread from cat to cat. The FIP virus mutates uniquely within each cat.

All of this raises the question: why do some cats develop FIP and not others? And what triggers the mutation? We don't have all the answers on this, but we know that there seems to be an element of genetic predisposition. Pedigreed cats seem to be three times as likely to develop FIP, and male cats are slightly more likely to develop FIP than females. The virus also seems to be opportunistic, and strikes cats with immature or weakened immune systems. This is why kittens and young cats with immature immune systems are most at risk. About 50% of FIP cases occur to kittens under 7 months, and 70% of FIP cases occur to cats 18 months or younger. Very often the advent of symptoms of FIP are tied to a stressful event -- for example surgery, change of environment, or another illness.


Once mutated, FIP takes several forms. The most recognizable form is effusive or "wet" FIP. In this form, the cat develops pockets of fluid in the lungs (pleural effusion) or around the belly (abdominal effusion). This form of FIP is the most rapidly progressing, and if untreated, can lead to death very quickly -- within days or weeks.

FIP can also manifest in a "dry" form, without any effusions. In many cases dry FIP will include neurological symptoms or ocular symptoms such as uveitis (an inflammation of the eye, which appears as color change, cloudiness or other ocular symptoms.) Dry FIP progresses more slowly, and cats may survive for months before succumbing. It is also more difficult to diagnose as symptoms tend to be more subtle. Neurological FIP is the hardest form to treat since the drug must cross the blood-brain barrier.

Most FIP cats of both types will have non-regenerative anemia, as well as a persistent fever.


Diagnosing FIP can be challenging in some cases. While some cats present textbook cases, many can present in unexpected ways. Typical FIP blood work will show low albumin, high globulin, high white blood cell count, low red blood cell count, high neutrophils, high protein, and high bilirubin. If an effusion is present, a sample can be taken and tested through RT-PCR -- a positive result confirms FIP diagnosis, however there is roughly a 30% chance of a false negative, so a negative result does not conclusively rule out FIP. A sample of fluid can also be tested via the Rivalta test, which can be done quickly and easily in private practice, and is highly predictive (although not conclusive) of FIP.


Until now, the only effective treatment was symptomatic treatment, which might allow management of symptoms for varying lengths of time. The most effective symptomatic treatment is with anti-inflammatories such as prednisolone, along with antibiotics to cover the depressive effect of steroids on the immune system. In some cases, non-steroidal anti-inflammatories may also be effective and avoid suppressing the immune system. Symptomatic treatment may be able to manage symptoms for as long as a year, but usually eventually fails due to complications from the weakened immune system. Treatment with anti-inflammatories is however useful in buying time, and can be used prior to pursuing curative treatment (as discussed below) if treatment is not immediately available.

In 2017, Dr Niels Pedersen from UC Davis published results from a trial that treated FIP cats with a protease inhibitor known as GC376. Protease inhibitors are drugs that inhibit the action of enzymes required for virus replication. Although this drug was effective in some cats with wet FIP, it was not effective for some forms of dry FIP. This is the first drug that showed any promise, and is currently being developed by Anivive Lifesciences with the intention to continue testing and seek FDA approval.

In 2019, even more promising results were published by Dr. Pedersen from a trial with a nucleoside analog known as GS-441524. Nucleoside analogues mimic natural nucleotide bases -- the building blocks of DNA and RNA -- and disrupt virus replication by replacing the normal bases with themselves, causing the virus to replicate something non-functional instead of a virus. Unfortunately this drug is currently not available in the United States, although it can be procured and is commonly used by vets in China.

A group of cat owners who have treated their cats for FIP has formed on Facebook, and people interested in learning more are encouraged to join the "FIP Warriors" group.

Links to additional information:

Efficacy and safety of the nucleoside analog GS-441524 for treatment of cats with naturally occurring feline infectious peritonitis

Feline infectious peritonitis: From fatal to treatable

Dr Niels Pederson: FIP Treatment

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