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The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.


Feline infectious peritonitis, or FIP, is a particularly heartbreaking disease. It occurs most often in kittens and is considered an incurable and fatal disease. We’ve talked before about how FIP develops and even about a drug (polyprenyl immunostimulant, PI) that has prolonged the life of some cats with the dry form of the disease.

To recap what we know about FIP, the disease is believed to be caused by a mutation in a ubiquitous and usually relatively benign virus known as the feline enteric coronavirus (FECV). This non-mutated virus has an affinity for intestinal cells and usually causes only mild gastro-intestinal symptoms, if it causes any symptoms at all in infected cats. However, the mutated virus (known as the feline infectious peritonitis virus, or FIPV) has an affinity for macrophages instead. (Macrophages, a specific type of white blood cell, play an important role in immunity.)

Currently, we can test for the coronavirus in cats but we do not have a test that can differentiate between the feline enteric coronavirus and its mutated form, the feline infectious peritonitis virus. This means that confirming a diagnosis of FIP is sometimes difficult.

Until very recently, we knew that a mutation occurred that transformed the non-virulent virus into its virulent form. However, we did not know what the mutation was nor where it occurred in the viral genetic makeup. Researchers at Cornell University’s College of Veterinary Medicine believe that has now changed. These researchers believe they have discovered what changes the feline enteric coronavirus into the feline infectious peritonitis virus in the form of a mutation in a spike protein cleavage site.

The details of this new discovery are somewhat complex. Suffice it to say that this specific mutation, according to the researchers, appears to be the reason the coronavirus is transformed from a benign occupant of the feline intestinal tract to a virulent virus that spreads rapidly through the cat’s entire body, almost always resulting in the death of the unfortunate infected cat.

This new discovery has many implications. Assuming this discovery proves to be valid, the next step is likely the development of a test that would be able to differentiate between the non-virulent coronavirus and the lethal mutant coronavirus. Obviously, a test like this would be valuable to veterinarians and cat owners struggling to establish a diagnosis and prognosis for these kittens.

It’s also possible that an effective and safe vaccine could be engineered based on the knowledge of this mutation and its effect on the virus. It’s likely that any vaccine will take time to become widely available but still the potential is there and offers some hope that eventually we may be able to prevent this awful disease.

Treatment options for cats suffering from FIP are currently limited and we have no treatment options that qualify as a real cure for the disease. The discovery of this mutation could potentially change that as well. As a veterinarian, it would be wonderful to be able to offer some hope to cat owners whose kittens are diagnosed with FIP.

On a broader scale, the discovery of this mutation could also have implications pertaining to coronavirus infections in other species, including people.

Obviously, there’s a lot that's still up in the air in regards to the significance of this discovery and any forthcoming developments resulting from it. Time will tell, but we’ll keep you informed.

Dr. Lorie Huston

Image: Levent Konuk / Shutterstock

Comments  3

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  • 07/08/2013 05:40pm

    Fortunately, I've never had a cat get this awful disease. I'm glad so much more is being learned about it.

    What about the genetics of the cat? Is it known, or being researched, if there is a genetic marker that would indicate that a cat's immune system would allow, or not allow, this mutation of the FECV?

  • FIP
    07/08/2013 07:00pm

    Once the virus has mutated, can't it be passed to other cats? Or do they think it always begins as a benign virus that mutates?

    It would be so wonderful to think that they might be able to come up with a vaccine so no kitty ever had to go through this again.

  • Update? Please Help!
    03/27/2014 10:10pm

    My cat was recently diagnosed with effusive FIP. He is considered "geriatric" since he is almost 13. This little guy is a big part of our family and if there is anything we can do to help him we want to do it! Please let me know if there are any updates on treatment for this awful disease!!!

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