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The many faces of Feline Infectious Peritonitis, part I
"Johnny was born the first part of November in 1998," says Christie Meyer, a behavior consultant and dog trainer in Fowlerville, Michigan. She'd volunteered to foster kittens and hand-raised the three littermates for the local humane society.
To protect her other pets, Meyer kept the kittens isolated from her adult white cat, Commit, until the babies tested negative for the most common killer cat diseases - feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV). After this health clearance, the litter mingled freely with the rest of Meyer's furry crew.
Meyer quickly fell in love with the smallest orange boy she named Johnny. Johnny purred all the time, and when he didn't sleep on Meyer's neck, he curled up with the dogs.
"Both dogs rolled onto their backs and the kittens would curl up between their legs on their belly," says Meyer.
While his two littermates appeared normal and eventually found new homes, Johnny never weighed more than a pound and a half. He began to run an intermittent fever, and when he also developed eye problems by the end of January, Meyer had little Johnny evaluated by the veterinarian where she worked. The doctor suspected Johnny the kitten had a deadly form of a common coronavirus. He was barely three months old.
Defining the disease
Feline Infectious Peritonitis (FIP) kills cats of all species, from house pets to cheetahs. It mostly affects young (under age 1) or very old domestic cats and experts estimate that up to 90 percent of pet cats are exposed to coronavirus during their lives.
Most commonly, cats catch coronavirus from contact with the infected stool from another cat. They may not get sick at all, or suffer only short-term diarrhea, then develop immunity, and recover. Immunity doesn't last very long, though, and cats continuously infect and re-infect each other particularly in multiple cat environments. For that reason, cats from shelters, catteries, feral colonies and the like are at highest risk.
According to FIP researcher Dr. Diane Addie, a senior lecturer in Veterinary Virology at the University of Glasgow, Scotland, about 10 percent of kittens and cats infected with coronavirus ultimately come down with FIP. Cats almost never get FIP from another FIP-infected cat. Instead, the harmless form of a coronavirus - the "good twin" - mutates into the "evil twin," the FIP form. While it sounds like bad science fiction, each FIP virus is unique to individual cats.
FIP virus targets and makes its home inside macrophages - specialized cells of the immune system. Once FIP virus passes through the intestinal wall into the bloodstream, these infected white blood cells turn into virus factories and carry their lethal cargo everywhere. That results in the cat's body attacking its own infected cells and tissues. A variety of symptoms develop, depending on which organ(s) become infected.
The effusive or "wet" form of FIP causes leakage of fluid into the abdomen so affected cats look like they have a beer belly. The "dry" form of the disease offers no specific outward sign. In either form of the disease, owners report the cats just don't "act right."
Not all cats develop every symptom but some of the more common ones include a fever that comes and goes; swollen belly and/or trouble breathing (wet FIP); loss of appetite; weight loss; eye problems (color changes, cloudiness, or spots); depression or loss of energy; seizures or balance problems. FIP has been called the purring disease, because these kitties seem to crave more attention and purr more, perhaps to help themselves feel better.
FIP frustrates and scares veterinarians and cat lovers alike because it not only kills cats. There's no easy way to diagnose the disease. The tests offered by some commercial laboratories are confusing at best and, at times, could be considered criminally misleading.
Tests gone wrong
Back in January 1999, Meyer's veterinarian relied on a commercial blood test which claimed to be able to tell the difference between the "evil twin" FIP-virus and the innocuous coronavirus. She was relieved when Johnny tested negative not once, but twice. So Meyer and her veterinarian looked for other causes for the kitten's illness. After describing Johnny's symptoms to specialists at Michigan State they decided to treat him for toxoplasmosis caused by a parasitic protozoan. Johnny's eye infection and transient fever were treated, but never went away.
"He ate like a maniac, but never gained, and never really acted sick," says Meyer. "Johnny was always happy, he was always social, and he always purred and interacted with me and the dogs."
But by early February, Johnny's appetite waned and he declined despite further treatment. The little orange boy died on Valentine's Day, before Meyer could keep the euthanasia appointment she'd made.
"I would have euthanized him at six weeks if he was a sick cat, but he never was," she says.
After Johnny's death, the University of North Carolina conducted extensive tests and confirmed he died from FIP.
"We never had a definitive diagnosis until he died. It was good to finally know," says Meyer.
Meyer has since learned that there is no test available to prove your cat has FIP or that he doesn't have the disease. In fact, an even more devastating and heart-breaking scenario has played out over the years when cats determined to be "positive" with so-called definitive FIP-tests are euthanized and yet are perfectly healthy.
Building a diagnostic wall
Niels Pedersen, DVM, Ph.D., of the University of California-Davis, is an expert on viral diseases and developed a blood test for antibodies to the enteric corona virus more than two decades ago. He hates the fact that this test has ended up killing healthy cats.
"The test is only one tool, but should not be used as a primary means of diagnosis," says Dr. Pedersen.
The confusion arises because common tests measure the "titer" (levels of immune components) in the cat's bloodstream. A cat exposed to and infected with a coronavirus (and there are several kinds) may test positive for the "good twin." But a positive titer simply means exposure took place and the virus left a fingerprint (antibody) behind.
"You don't get FIP unless you have antibody," says Susan Little, DVM, a feline specialist practicing in Ottawa, Canada, and vice president of the WINN Feline Foundation. However, the presence of antibodies alone does not mean your cat has FIP, nor does it predict a cat will get sick.
To complicate matters further, different labs offer variable interpretations of what constitutes a "negative" or "positive" corona titer level. Your kitty may test positive from one lab, and negative from another using the same sample. False positives and false negatives can result from contamination, too.
So, what can be done?
"Build a diagnostic wall," says Melissa Kennedy, DVM, PhD, an assistant professor and board-certified veterinary microbiologist at the University of Tennessee.
While a single test or symptom may mean nothing by itself, taken together, brick by brick,they can build a strong presumptive diagnosis, sort of a smoking gun that points to the disease.
"If everything else looks like FIP and the serology [tests] doesn't, then ignore the serology," says Kennedy.
The feline coronavirus (good twin) can be detected by a variety of tests that evaluate blood values, detect antibodies to the virus, or find the virus itself in the cat's plasma, whole blood, sometimes the feces, or even the straw-colored fluid commonly found in wet FIP. In addition, blood changes typical of FIP infection such as anemia and elevated protein levels can be strong evidence.
But the only definitive test for FIP must be performed on tissue samples usually only available after the cat has died. In rare cases these samples can be obtained while the cat's alive. That involves ultrasound-guided "true cut" biopsies of the typical FIP lesions on a living cat, but only when the feline remains healthy enough to withstand the anesthetic procedure.
Pederson and others believe environmental influences and genetics share equal blame for the disease. Eliminating the virus from the environment may be next to impossible-. Yu'll learn more about that in the next article. But researchers suspect some cats inherit a susceptibility to FIP that allows mutation to take place, while others inherit resistance.
The notion is supported by an interesting mouse study that showed when a particular gene (interferon-gama) was absent or deficient, the mice developed peritonitis that paralleled FIP. Researchers now investigate to see if FIP-resistance might be linked to interferon-gama response, or to some other mechanism. UC-Davis seeks to develop a genetic test to help identify those cats that are more or less likely to develop FIP.
"You can genetically define cats that are resistant or susceptible," says Pederson.
Why is that important?
If susceptibility and resistance can be predicted, responsible cat fanciers may be able breed FIP-resistant kittens and perhaps ultimately reduce incidence of this deadly disease.
"We're still five years away, but we do it in other species," says Pedersen. "We'll do it in cats."
This article recaps information presented by a panel of experts at the 2005 Western Veterinary Conference FIP Symposium. Watch for the conclusion in "Part 2: FIP HOPE FOR THE FUTURE," covering experimental treatments and management issue.
Amy D. Shoja is a nationally-known pet care specialist, and author of more than a dozen pet books. She can be reached through her website www.shojai.com. © 2005 Amy D. Shojai
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Very informative article, and one I'll be saving to print out for those who rely on that useless test. 
I hate to think of how many cats are needlessly killed because people jump at the 'positive' diagnosis! 
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