Feline Infectious Peritonitis (FIP)

Revised August 25, 2019

FIP is a particularly nasty disease—one that causes great confusion and distress. The name itself is misleading; the only absolutely true point about the name is the “feline,” since it is not terribly infectious, nor is it always peritonitis (inflammation in the abdominal cavity). Unfortunately, the disease is nearly 100% fatal in its active form.

As a rule, FIP develops primarily in young cats under 2 years of age, or in older cats age 10 and up. It is fairly rare in the middle years. A study of more than 800 cats in Great Britain found that in homes where a cat had died of FIP, the transmission rate to other cats in the home was less than 5%. Since these other cats continued to go outside where they could also have been re-exposed to another source, it is clear that FIP does not easily pass from one cat to another.

However, purebred cats and kittens seem more susceptible, and crowded catteries seem to be the most problematic sitaution for the developmetn of FIP.

FIP is considered to be caused by a virulent form of an otherwise harmless bug called Coronavirus. This virus causes mild diarrhea in very young puppies and kittens, but is generally self-limiting and doesn’t cause much of a problem. However, the virus is also found in cats who do ultimately contract FIP, in which it is thought to have mutated to a virulent form (though this has never been proven).

Saying that Coronavirus causes FIP might be a little like saying “flies cause garbage” just because the two are usually found together. Whether or not coronavirus is the real trigger is unknown. Many perfectly normal cats who will never develop FIP will test positive for Coronavirus; in my experience, about 40% of normal cats will have a positive test. This is only a reflection of the cat’s having been exposed to the virus at some time in its life, and doesn’t mean very much otherwise.

FIP is very difficult to diagnose correctly, at least while the cat is still alive. Most confirmed cases are recognized at necropsy (the technical term for an autopsy on a non-human animal). The early symptoms are vague, and commonly found with many other conditions, not just FIP. Symptoms include poor appetite, failure to thrive (in kittens), weight loss, ratty-looking fur, eye problems such as uveitis (inflammation), fever, anemia, lethargy, jaundice, neurological symptoms, and what vets refer to simply as “ADR”—which stands for “ain’t doin’ right.” FIP is typically diagnosed when a symptomatic cat has a positive test for Coronavirus along with other typical laboratory abnormalities that support the diagnosis.

The actual FIP disease symptoms are actually caused by the cat’s own immune system. For some reason, the immune system over-reacts and creates many patches of white blood cells that produce tons of antibodies. In some cats, this results in chronic inflammation, usually without clear symptoms; this is called “dry” FIP and is very hard to diagnose correctly. In the “wet” or “effusive” form of FIP, the body also produces large amounts of fluid—usually in the abdomen but sometimes in the chest instead. The fluid is characteristically yellow and sticky; its high protein content is diagnostic for FIP. Both forms of FIP usually cause rapid deterioration and death.

There is a vaccine for FIP, but most experts do not recommend it. The vaccine is not very effective, and it can actually cause worse problems than it purports to solve. In challenge trials, vaccinated cats got sicker and died sooner than unvaccinated cats.

Treatment for FIP has been difficult. Studies have shown variable results with interferon, a drug called Trental (pentoxifylline, a blood thinner), along with prednisolone (a steroid) to suppress the immune system’s over-reaction and inflammation. These drugs may reduce symptoms and prolong the cat’s life, but there is little evidence that they provide a true cure for FIP.

However, in the last few years, two promising drugs have been developed: GS-441524 (GS) and GC374 (GC). They have been shown to reverse the progression of FIP in clinical trials at the University of California at Davis  involving several dozen infected cats. The drugs are not (yet) FDA approved, although that process is ongoing. However, the Chinese black market has been quick to capitalize on the desperation of people whose cats are sick right now. Lead researcher Dr. Neils Pedersen posted this article to explain the situation. For the most current information, check out the Facebook group FIP Warriors.

It’s  hard to recommend specific preventive measures for such an elusive disease. However, a nutritious diet, minimal vaccination, and appropriate immune-supporting supplements are always the best bet to create optimal health for your cat. We recommend a primarily wet food diet (raw, canned or homemade) along with four specific supplements: digestive enzymes, probiotics, antioxidants, and omega-3 fatty acids.

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