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FIP Is a Dreaded and Poorly Understood Disease in Cats

Feline infectious peritonitis is difficult to diagnose, even harder to treat, and almost always fatal.

 |  Oct 22nd 2013  |   8 Contributions


No three letters have more power to strike fear into the hearts of cat lovers than F, I, and P. Combined, they form an acronym for feline infectious peritonitis. FIP is the most dreaded disease in veterinary medicine and a big threat to a cat's health and survival.

FIP most frequently strikes young cats. It usually progresses insidiously and causes weight loss, poor appetite, and deterioration of body condition. There are no proven treatments for the condition. There is no definitive blood test for the condition, and diagnosing FIP can be challenging. Sadly, cats who show symptoms of FIP almost always die.

FIP is caused by a type of virus called coronavirus. There are two types of feline coronavirus. One, called feline enteric coronavirus, is extremely common. It causes mild, transient diarrhea, and it is endemic in many catteries, shelters, and rescue facilities. The second coronavirus is the one that causes FIP. The FIP virus appears to be a mutant form of the enteric coronavirus. Most experts believe that FIP occurs when enteric coronavirus already infecting a cat undergoes a mutation. Some cats appear to be able to suppress FIP if they mount a rapid immune response; others are not able to suppress the virus. It is not known why some cats are able to clear the virus while others are not. Those that cannot clear the virus generally suffer fatal results.

Photo of Dr. Eric Barchas by Liz Acosta

Cats with FIP develop one of two syndromes. Wet FIP is most common. Cats with this form of FIP usually develop effusions (fluid) in their abdomen or chest. The fluid may result in abdominal distention or difficulty breathing.

Cats with dry FIP develop focal areas of inflammation called granulomas. The granulomas can develop in the abdomen (creating a mass effect) or in other areas; I recently diagnosed a cat with FIP after a granuloma formed in his nasal cavity (causing nasal discharge and noisy breathing) and then spread into his brain (causing blindness and tremors). Both forms of FIP cause appetite suppression, weight loss, failure to thrive, and death. Affected cats are most often less than two years of age.

Diagnosing FIP is a challenge. The condition is often diagnosed based upon clinical suspicion when a young cat develops unexplained symptoms consistent with FIP. Cats with FIP may have alterations in blood cell lines and blood protein levels that are typical of but not exclusive to the condition. Blood tests for coronavirus antibodies may offer some insight into the diagnosis, but the blood tests cannot differentiate between the two forms of coronavirus. A cat with a positive coronavirus titer may only have been exposed to the enteric form of the virus.

The most reliable test involves DNA analysis of fluid collected from the abdomen or chest. This test generally cannot identify the dry form of FIP. Sadly, autopsy is one of the most common ways that dry FIP is diagnosed.

Tabby cat by Shutterstock.

Complicating matters further is the fact that there is no effective treatment for FIP (although there have been rare reports of cats in whom the disease resolved spontaneously). Steroids are sometimes administered for palliative effects; they may transiently increase appetite and decrease the severity of symptoms experienced. One study reported successful treatment of FIP with feline interferon omega. Sadly, a larger study with a similar agent negated those results. Other antiviral therapies have shown some promise in vitro, but have not yet been shown to offer clinical benefit to cats with FIP. Polyprenyl immunostimulant has shown promise in one small study, but its use is still highly experimental. In short, there is no proven treatment for FIP and the condition carries a grave prognosis. The overwhelming majority of cats with FIP die.

Prevention of FIP also is difficult. A coronavirus vaccine is available but its efficacy is dubious. The enteric form of coronavirus is endemic in most shelters and catteries and it is virtually impossible to eradicate. However, the incidence of FIP appears to be lower in facilities in which cats experience good hygiene, less stress, and less overcrowding.

There is one and only one bit of a silver lining on the dark cloud of FIP. Although the disease is technically contagious (and its name contains the word infectious), the disease does not frequently spread from cat to cat. The disease appears to develop most frequently as a unique mutation of the enteric coronavirus in individual cats. Also, the mutated virus that causes FIP usually is not shed by infected cats in significant quantities. Furthermore, previous exposure to the enteric form of coronavirus may offer protection against FIP to individual cats -- unless the enteric coronavirus mutates within them.

Orange and white cat by Shutterstock.

With that said, experts still recommend that no new cats be introduced into a home touched by FIP for at least three months. They also recommend that only mature cats (older than two years) be adopted into such homes because they are less susceptible to the condition.

In my 13-year career I have seen only one instance in which a client lost a cat to FIP, then adopted a new kitten, and subsequently lost the new cat to FIP as well. This is consistent with the low transmissibility of the disease among cats. That low transmissibility, however, is cold comfort to any person whose life has been touched by this terrible disease.

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