There Is No Test For FIP
Published February 2014

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Feline Infectious Peritonitis (FIP) is a fatal viral disease of cats. There is no such thing currently as a definitive test for FIP, yet occasionally people will say that their cat has tested positive for FIP.

Mostly likely, such statements are the result of confusion regarding the details of the relationship between the feline coronavirus and the FIP virus.

The Relationship Between The Coronavirus and FIP

There are many different strains of feline coronaviruses and the majority of cats in a cattery are exposed to coronavirus as kittens.

Most strains of coronavirus do not cause any disease symptoms. During the initial viral infection, the cat's immune system produces antibodies against the virus, but does not eliminate it, and the virus continues to reside in the intestinal tract, causing no problems. 

Strains that cause a mild intestinal disease (diarrhea) are called Feline Enteric Coronavirus (FECV).

A relatively small percentage of the cats that have been infected with coronavirus develop fatal FIP. It is suspected that FIP develops when the relatively harmless coronavirus MUTATES in the individual cat and the infection progresses into clinical FIP. The mutated virus is then referred to as feline infectious peritonitis virus (FIPV).

FECV and FIPV are connected only because cats that have FIP also have the coronavirus. The opposite is not true.

Most cats that develop FIP are under two years of age.

Cats with weak immune systems are most likely to develop FIP,
including kittens, cats already infected with feline leukemia virus (FeLV), and geriatric cats.

Testing For Coronavirus

There are two tests that can confirm that a cat has been exposed to coronavirus:

  • The Coronavirus Antibody Titer Test: measures the cat's response (antibody titer) to the coronavirus. Titers greater than 1:8 are considered corona virus positive. Positive values range from 9 to greater than 2000. These titers are not a good predictor of a cat developing FIP.
  • PCR & DNA testing: More recently, a DNA-based PCR test has been developed that identifies the actual presence of the coronavirus itself, as opposed to identifying the cat's response (antibody titer) to the virus. This PCR test also can not distinguish the benign coronavirus from the FIP virus.

The High Incidence Of Coronavirus In Cats

If, as scientists believe, FIP occurs when the coronavirus mutates, it means that any cat that carries any coronavirus has the potential to develop FIP. Unfortunately, the number of cats that carry coronavirus is very high:

  • As many as 40% of cats in the general population test positive for coronavirus.
  • Up to 90% of cats in catteries or multi-cat households carry coronavirus.
  • Kittens are usually infected with coronavirus by 10 weeks of age.
  • Only 5-10% of coronavirus-infected cats develop FIP in a cattery setting, and the incidence is much less in a single-cat household. 

The presence of coronavirus or its antibodies in the blood stream DOES NOT mean that the cat has FIP. Because so many cats test positive for coronavirus yet never develop FIP, testing for coronavirus alone is not helpful in confirming a diagnosis FIP or predicting which cats have a greater risk of developing FIP.

There Is No "FIP titer test" or "FIP test"

There is no such thing as an test for FIP. There is only a test for coronavirus.

  • Most perfectly health cats from a multiple cat situation will test positive for the coronavirus.
  • A positive coronavirus test or titer DOES NOT mean the cat has FIP.
  • We are not able to differentiate between FIP-causing strains of coronavirus and those that cause little or no disease.

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