A Word About FIP

By Cris Bird, Dr.P.H.

When you look at cattery ads and websites, you often see, “We guarantee our kittens free of feline leukemia and FIV.” Sometimes you see guarantees that kittens are free of FIP, as well.

It is reasonable for a breeder to claim that her kittens are free of feline leukemia and feline immunodeficiency virus (FIV). There are good screening tests for those diseases. The tests are not perfect. No test is. But they are very, very good, about as good as screening tests can get. If a breeder tests all new cats for feline leukemia and FIV and does not allow the new cats to join her other cats until she is sure they are negative for those diseases, and if she never allows her cats to wander outdoors, she can be confident, and so can you, that her kittens are leukemia and FIV-free.

But FIP is quite another thing.

FIP should not be confused with FIV. They are two entirely different diseases. There is a good test for FIV, but there is no valid screening test for FIP and no cure for the disease. FIP is nearly always fatal once symptoms have appeared, so this is a huge concern.

Let me say it again.

Although some breeders advertise that they have tested their cats for FIP or that their catteries are “FIP negative,” those claims are meaningless. There is no laboratory test that can guarantee that any cat is free of FIP.There are several tests that have been developed for FIP, but so far none has proved to be even a moderately good screening test. In fact, the situation is so miserable that breeders can test every cat and get negative results even in the middle of an FIP epidemic in the cattery.* On the other hand, cats can have high coronavirus titers (the coronavirus titer is one of the “tests” for FIP) when they don’t have FIP at all but instead are only fighting a harmless coronavirus, something that could easily happen after a cat changes homes and encounters new but harmless family “bugs.” FIP testing is a complex area of veterinary medicine and not all vets adequately keep up with developments in that area. Due to occasional veterinary misinterpretation of “FIP tests,” some cats have been euthanized who had temporarily high but harmless coronavirus titers, cats who otherwise might have lived long healthy lives.

So how can you tell whether the risk of FIP is low in a cattery? Well, mainly by how clean it is, how happy the cats are, and how uncrowded the cattery is. Having an uncrowded cattery with happy, unstressed cats is very, very important. Breeders can use good cattery management to reduce the risk of FIP. A cattery that is at low risk for FIP is one that has only a few felines, especially young felines, on the premises at any given time. The fewer, the better. There are reputable breeders who breed more than a few litters per year and have excellent reasons for doing so, but the fact is, the more adult cats are housed together and the more litters are bred on the same premises in a given year, the higher the risk of FIP.**

The bug that causes FIP is one type of coronavirus from a family of hundreds of harmless coronaviruses. The harmless coronaviruses, the ones that do not cause FIP, are common as dirt, and research has shown that in a multi-cat home they are nearly always present. Unfortunately, it appears that at any given moment a harmless coronavirus may mutate into a dangerous FIP virus. Currently, it is not possible to eliminate all types of coronaviruses. That would be like trying to keep every mote of dust out of a home, just not practical. FIP can therefore develop in any cat in any home. In one published case, a pet cat living strictly indoors by himself for eleven years developed FIP.

Fortunately, FIP does not often develop in adult cats. FIP most often strikes at age 6 to 8 months, and it strikes somewhat often in kittens up to 1 1/2 years old. Kittens are much more likely to develop FIP than adults because kittens have immature immune systems (especially when they are less than a year old). No one knows for certain why the big older kittens develop FIP more often than the young babies, but it may be that FIP is a complex disease that takes a long time to develop. It starts in very young kittens, but the first symptoms are not seen until the kitten is much older.

According to one recent estimate, even very well run catteries and shelters may have something like 2 percent of their kittens develop FIP, and virtually all of them that do will die of the disease. To put it another way, it’s virtually impossible to rescue cats or breed cats for any length of time without eventually encountering FIP. Cases tend to occur in clusters. That is, the cattery or shelter may go for several years without a single case of FIP, then begin to have cases occur regularly, and finally FIP stops appearing for another few years.

Whether or not a kitten gets FIP seems to depend primarily on two things: (1) stress and (2) genetics.

To put it another way, the development of FIP depends on the strength of the feline immune system. Stress impairs the immune system in most animals and in humans. Very young cats under stress are more vulnerable to FIP than other cats. Veterinary researchers have noticed that FIP frequently strikes after a stressful event, such as changing homes, declaw surgery, or after a period when the cat’s beloved owner was out of town.

Cats that have inherited weak immune systems are also vulnerable to FIP. In fact, researchers estimate that genetic factors account for about 50 percent of the risk of FIP. Although the amount of inbreeding in a cat’s pedigree did not seem to predict FIP in one study, that may be because of the study’s limitations. In epidemiologic studies, the ability to detect the cause of a disease will in part depend on how much variation in exposure there is in the population studied. In plain English, if you study a group of pedigreed cats, all of whom are actually fairly inbred, they may not be different enough from each other for researchers to detect a significant genetic difference in their risk of FIP. It can appear as if genes don’t matter when in fact they do.

This kind of research limitation is particularly likely if a genetic predisposition to FIP is the result of dozens of genes (polygenes).

Experimental evidence points to the importance of  genes in designing the feline immune system and thereby affecting vulnerability to FIP. In one study, for example, the ability of each cat to produce interferon gamma seemed to determine whether the cat did or did not come down with FIP symptoms and die. Interferon gamma is one of the tools the immune system needs to fight certain types of disease.

I think the evidence is strong enough to take seriously. In my cattery, I have apparently had a very low incidence of FIP. As this article was written, we had never had a case of FIP occur in cats or kittens living with us, including no unexplained deaths of cats or kittens, and we only once had ever had a kitten develop FIP after leaving us. That particular kitten developed FIP about 8 months after he left, at age 11 months old. He was from the only litter we had ever produced that had somewhat closely related parents. The mother of the kitten was the half niece of the father; that is, the maternal grandmother of the kitten was the half sister of the kitten’s father. Perhaps that was just bad luck, just random chance. Or perhaps it was the shared genes the parents had that caused their kitten, just the one kitten out of a litter of five, to have a weaker immune system and be more vulnerable to FIP than our other kittens.

I will never know for sure. I neutered the father of the kitten; he never sired another litter. The mother of the kitten had many litters with other studs and never had any other offspring come down with FIP.

But it is just one more reason, out of hundreds of other reasons, to avoid breeding closely related cats and, indeed, to actively search for and import fresh bloodlines to expand the gene pool of our cattery and of the breed as a whole.

For those of you who are looking for a purebred kitten or cat to join your family, the bottom line is simple. If a breeder breeds long enough, sooner or later that breeder will encounter a case of FIP in the cattery. It’s not a question of if; it’s a question of when. Good breeders can’t completely prevent FIP. There is no such thing as an “FIP-negative cattery.” But breeders can make FIP a rare event via wise cattery management.

Remember: There is no reliable test for FIP. However, you can evaluate risk by looking at cattery conditions. Breeders with multiple litters perpetually present and large numbers of cats crowded together have a high-risk situation. A breeder with very few adult cats, who raises only a few litters per year, and who keeps the premises immaculate and the cats well fed and uncrowded andhappy, has the lowest possible risk of FIP. §

For more information about FIP, we encourage you to visit the SOCKFIP website (click logo below), where you can learn about the latest research at the University of California at Davis and the war the cat fancy is waging against FIP. You may also want to consult the excellent article by Dr. Susan Little, a veterinarian who specializes in cats and who also had breeding experience when she was younger. She knows more than most vets about the theory and practical issues surrounding prevention of FIP .


* Epidemics of FIP are rare. FIP does not usually behave like an infectious disease. However, epidemics do occur on rare occasions. Researchers speculate that epidemics may be caused by many closely related cats that are genetically susceptible to FIP all living in the same cattery. Or epidemics may be the result of extraordinarily virulent, rare strains of coronavirus that have a very high conversion rate to FIP or special properties that most FIP strains do not have. Or epidemics conceivably may be the result of an entire group of cats being subjected to extremely stressful conditions.

** Yes, I am aware, veterinary research data show that risk increases up to a point, but does not increase significantly after that. That is, if breeders have a very small number of cats they have a low FIP risk, but as they get beyond  a handful of cats, the risk increases dramatically and then plateaus. Bear in mind that that is the AVERAGE scenario. With the limited funding available for veterinary medical research, very rough estimates of average risk are usually the best they can achieve.

However, as a famous biostatistician, Stephen Jay Gould, once said, “The mean is not the message.” If you change the average behavior of the average breeder, the curve plotting risk per cat is likely to change, also. To put it another way, what good individual breeders do will always count for something. Stress is a factor and genes are a factor. If a breeder has a fairly large number of cats, but is able to keep them all quite happy and uncrowded and genetically immunologically sound, it is plausible (though admittedly we do not yet know for sure) that the risk of FIP in that breeder’s cattery will be much lower than the average usually seen with large numbers of cats. That breeder would be an outlier on the curve, but the results would be real.

On the other hand, the more cats a breeder owns, the harder it gets to keep them all happy and unstressed. Thus, as the number of cats rises, a breeder eventually, no matter how skilled she is, gets closer and closer to having more cats than she can care for. If nothing else, she will inevitably have to farm out some of the work to hirelings or relatives. Without individual attention, you can’t be certain a cat is doing well.

Copyright © 1996-2014 by Dr. Cris Bird of Sarsenstone Cattery. You may not redistribute it in any form without the express written consent of the copyright holder.

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