Is My New Cat at Risk of FIP Carried by My Other Cats?


Here is a recent question I received from a reader.

I found a cat last night half frozen. I brought it inside and took care of it, but my issue is that I was told my two cats have the virus FIP (I lost two of my other cats four years ago from FIP and they are carriers) and can’t have any other cats in my house. I really would love to add this kitty to our family but I’m confused on the information I’m reading online about FIP.

Thank you,


I’m not surprised that Carrol is confused by the information she has found online about FIP. FIP is naturally confusing, and anyone who claims to understand it fully is either lying or fooling himself.

FIP is short for feline infectious peritonitis. It is, without a doubt, the most dreaded infectious disease of cats. It is also one of the most complicated diseases known to veterinary medicine.

Here is some of what is known. FIP is caused by a mutant form of a nearly ubiquitous pathogen called the feline coronavirus. I have read estimates that 50 percent of cats in single cat households are infected with coronavirus. It is furthermore estimated that 80 to 90 percent of cats living in multiple-cat households are infected. The overwhelming majority of cats infected with coronavirus do not develop FIP. Most cats live their entire lifetimes with the relatively benign form of the virus, and they rarely develop symptoms other than mild transient gastrointestinal upset.

FIP occurs when coronavirus mutates. Most experts believe that the majority of cases of FIP develop as unique mutations that occur in cats already infected with the relatively benign form of coronavirus. A cat who has never been exposed to coronavirus may be at risk of directly catching FIP. However, it is believed that a cat who is already infected with the benign form of coronavirus is unlikely to directly catch FIP.

The worst thing about FIP is that it is essentially untreatable and, in the overwhelming majority of cases that are diagnosed, fatal. A number of treatments have been proffered, but none has been shown to work. For instance, some studies have shown that treatment with steroids may slow the progression of the disease but does not cure it. Other ballyhooed treatments such as propentofylline and feline interferon omega have been shown in studies to have no impact on life expectancy or quality of life. A final proposed treatment, polyprenyl immunostimulant, is unproven, experimental, and not commercially available. In short, there is no known effective treatment for FIP.

FIP also is a bear to diagnose. The definitive way to diagnose it is to run DNA analysis of abdominal fluid in sick cats. However, there is no way to determine whether a healthy cat is an FIP carrier. Coronavirus titers can be run on healthy individuals, but the titers do not differentiate between the benign form of coronavirus and the deadly FIP.

Carrol, I am guessing that your two cats have tested positive for coronavirus. However, it is not clear that they harbor FIP. The mere fact that they are alive four years after the last two died is evidence that they harbor the benign form of the virus.

However, this situation remains dangerous for all cats in the house nonetheless. A leading contributor to the conversion of benign coronavirus to FIP is stress, and there currently are a lot of potentially stressful circumstances for all three cats in the house. Specifically, rehousing, adding a new cat to a house, and having more than two cats in a house are all famously stressful for cats. This places all three cats at risk.

You have already done the most important thing: You have quarantined the new addition. This quarantine should last at least one month, and much longer if possible. The new cat should see the vet, be dewormed and vaccinated (although you should note that the American Association of Feline Practitioners does not currently recommend the coronavirus vaccine), and tested for diseases such as FIV and FeLV, which could spread to your existing cats. The vet can also run a coronavirus titer on the new guy to get a better understanding of the situation.

Although this situation does pose potential risks for all three cats, it is not a foregone conclusion that adding the new individual will prove fatal for anyone. If you are cautious, it may be possible to expand your family of cats.

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