Feline Infectious Peritonitis (FIP) is one of the most frustrating cat diseases that I have ever had to deal with. We usually can’t prevent it, we can’t really treat it (other than symptomatically), it’s relatively common (more so than we used to think), and it’s invariably fatal.

Don’t lose heart though, it looks like things may be about to change for the better.

First a bit of background. FIP is caused by a coronavirus. This particular virus infects a lot of kittens, usually causing some mild diarrhea, and then most often is never heard from again. In some cats, however, the immune system is unsuccessful at fighting it off and the virus mutates into a form that results in the disease FIP.

The most common symptoms of FIP are pretty nonspecific, including:

• fever
• lethargy
• depression
• loss of appetite and weight

Some cats develop eye infections, while others might have neurologic abnormalities or difficulty breathing.

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.

Diagnosing cats with FIP is not easy. Immunological testing is available but is not good at differentiating between individuals that have been exposed to the "diarrhea-causing" form of the virus versus those that 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 the cat’s symptoms also all point in that direction.

The dry form of FIP is often 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.

Now that I’ve thoroughly depressed you, let me give you the good news.

A new drug is currently under investigation that might help cats with the dry form of FIP. The drug is called polyprenyl immunostimulant (PI); it is a medication derived from plants that helps the body fight off viral diseases. The studies are ongoing, but some of the FIP kitties being treated with PI are doing surprisingly well. One cat has lived for five years and others have seen a dramatic decrease in their symptoms and seem to be thriving. Unfortunately, not every cat in the study responded so well to PI, and previous research did not show any benefit in treating cats suffering from wet FIP with the drug.

Still, any hope in the FIP arena is reason to celebrate.

PI should gain conditional licensure for treatment of rhinotracheitis in cats in the not too distant future. Once it is available, veterinarians will have the option of using it "off-label" for FIP cats when they feel it is in their patient’s best interest.

On a final note: This is my last post for The Daily Vet, but have no fear, I’m just moving "down the dial" here at petMD to take over Fully Vetted. Dr. Lorie Huston will be taking over these Monday cat blogs next week. I’m looking forward to hearing her take on all things feline.

Dr. Jennifer Coates

_{Pic of the day: "Taek mah hand, mastah." by stratman2 (Flickr backlog!)}