Skip to main content

Feline Infectious Peritonitis (FIP) is a terrible diagnosis. Veterinarians don’t have much to offer cats with FIP other than symptomatic treatment that, at best, only keeps them comfortable for a relatively short period of time before death inevitably follows.

We may be on the verge of a big breakthrough in FIP treatment, however.

First a bit of background. FIP is caused by a coronavirus. This particular virus infects many kittens, usually only causing mild diarrhea from which the kitten recovers with little or no treatment. For most individuals, that’s the end, and the virus is never heard from again. But for other cats, the virus remains dormant in their bodies for a period of time before mutating and causing the disease we call FIP.

If cats can’t fight off the FIP virus, they develop a range of nonspecific symptoms like fever, lethargy, depression, poor appetite, and weight loss. In the “wet” form of FIP, fluid accumulates in the abdomen or chest. If no such fluid accumulations are found, a cat is said to have “dry” FIP. Neurologic abnormalities, difficulty breathing, and eye problems are all also possible with FIP.

Diagnosing cats with FIP is not easy. Immunological testing is available but is not good at differentiating between individuals who have been exposed to the “diarrhea-causing” form of the virus versus those who have current FIP infections.

In cats with wet FIP, the fluid is often fairly characteristic—you can stretch long strings of it out between your fingers because of its high protein content. This may be enough to lead to an FIP diagnosis when a cat’s symptoms also all point in that direction.

The dry form of FIP is usually a diagnosis of exclusion, meaning that a veterinarian has to rule out other potential causes of a cat’s symptoms and then is left saying “there’s not much else left to explain what’s going on; it’s probably FIP.” Tissue biopsies are an option when a definitive diagnosis is desired.

Once a cat has been diagnosed with FIP, owners have to choose between palliative care and euthanasia if a cat’s poor quality of life warrants it, but that might be changing if the results of a recently published paper hold.

Scientists gave FIP virus to eight cats. Once those cats reached a stage where their symptoms were bad enough that under normal circumstances they would inevitably die (some did receive medication and fluid therapy to keep them comfortable), treatment with an experimental, antiviral protease inhibitor called GC376 began. The cats received subcutaneous injections twice a day. Unfortunately, two cats were euthanized because their condition deteriorated to an unacceptable level, but the other six cats made near miraculous recoveries. According to the authors of the paper:

All six remaining cats showed rapid improvement in attitude and resolution of fever (Fig 3B). The profound absolute lymphopenia [low counts of a certain type of blood cell that fights infection] observed in all cats prior to antiviral treatment also returned to normal before the next blood testing one week later (Fig 3D) and weight losses were reversed and normal growth resumed (Fig 3C). Ascites [fluid buildup in the abdomen] and scrotal swelling indicative of peritonitis also gradually resolved after a week of antiviral treatment. All cats that received antiviral treatment for 14–20 days appeared normal by clinical observation and laboratory testing. The six recovered cats… have remained healthy showing no signs of relapse during an observation period up to 8 months. These experiments demonstrate that the protease inhibitor was able to reverse disease progression when treatment was initiated at advanced clinical stages of FIP.

If future studies go on to confirm that this potential drug is effective against naturally-occurring FIP, the disease may no longer be a death sentence for infected cats.


Reversal of the Progression of Fatal Coronavirus Infection in Cats by a Broad-Spectrum Coronavirus Protease Inhibitor. Kim Y, Liu H, Galasiti Kankanamalage AC, Weerasekara S, Hua DH, Groutas WC, Chang KO, Pedersen NC. PLoS Pathog. 2016 Mar 30;12(3):e1005531. 

Help us make PetMD better

Was this article helpful?