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Feline Infectious Peritonitis is an invariably fatal infectious disease of cats which is seen most often in multicat households or catteries, or following exposure to other cats for example at cat shows, or possibly visits to a veterinary premises.. It is rarely seen in cats kept by themselves with no contact with other cats..

The disease is caused by an immune complex formed by a coronavirus (or viral antigen), antibodies and complement. 

The cat becomes infected by the virus:

  • By contact with the virus in cat faeces - litter trays
  • By contact with saliva from infected cats - mutual grooming, shared food bowls
  • By inhalation of the virus
  • Across the placenta

Cats that do not have antibodies to the virus do not develop the disease.

Breed Occurrence
Pedigree kittens and Cheetahs may be genetically more susceptible to develop FIP. IN one survey 80% of cats attending a cat show in the UK had a positive blood test for exposure to FIP.

The disease most often occurs in cats with some form of depressed immune system activity - eg it can occur secondary to infection with Feline Leukaemia Virus, or  Feline Immunodeficiency Virus

The clinical signs result from damage in different tissues caused by the immune complexes that are formed (see above) and inclu
de :

  • The peritoneum - leading to peritonitis and free fluid in the abdominal cavity 
  • Kidney
  • Liver
  • Uvea - causes inflammation in the eye (uveitis, or iritis)

Two basic forms of disease are described and these have different signs associated with them :

  • Effusive FIP
    • Abdominal swelling due to free fluid in the abdominal cavity (called "ascites")
    • Weight loss
    • Hard/firm masses can be felt in the abdomen
    • Slight increase body temperature
    • If free chest fluid as well - get dyspnoea, tachypnoea, muffled heart sounds on auscultation, pale mucous membranes
    • May have jaundice
    • Cat may be dull
    • Cat may be off it's food
  • Non-effusive FIP
    • Weight loss
    • Increased body temperature
    • Cat may be dull
    • Cat may be off it's food
    • Some cats have iritis - iris colour changes to brown, or to green from blue.
    • The retina is involved in some cases - cuffing of the retinal vessels - appearing as fuzzy grey lines alongside the blood vessels
    • About 12% of cats have neurological signs including ataxia, lameness, paresis, tremors, hyperaesthesia, behavioural changes, nystagmus, blindness, cranial nerve deficits and seizures. 75% of cats with neurological signs have hydrocephalus - which can be identified on CT-scan.

Two other forms of disease occur occasionally :

  • Intestinal FIP
    • Lesions (granulomas) occur in the intestine or colon.- feel thickened on examination
    • Signs include constipation, diarrhoea or vomiting
  • Post-natal Death
    • FIP can cause death in 7-8 week old kittens. This occurs presumably when they produce antibodies to infection that they contracted soon after birth, or in utero

Cats can carry the virus for many months or years before the disease develops.

There is no single test for FIP. 

Ideally intestinal or other tissue samples are needed to confirm the presence of the virus by immunofluorescence techniques.

Non-specific laboratory findings in FIP include :

  • Serum albumin:globulin ratio decreases because globulin concentrations increase
  • Total serum protein is high
  • There is a neutrophilia with a shift to the left
  • Non-regenerative anaemia in some cats
  • Heinz bodies  are present
  • High bilurubin - if liver necrosis present
  • High CSF protein if showing neurological signs

The effusion is a modified transudate and may be 

  • Colourless
  • Straw coloured
  • Pink
  • Sticky (viscous)
  • Occasionally white (chylous)

Serological testing for antibodies is widely used and is useful if interpretation is done carefully. The presence of a positive titre only means the cat has been in contact with a coronavirus - it does not necessarily mean that the cat has the disease FIP which requires immune-complex formation.

There is a specialized ELISA test which detects the immune-complexes and this is specific for the disease - but it is not generally available yet.


There is no specific treatment against FIP virus.

There is no need to treat cats that have a positive blood test, but which do not have evidence of the disease However, they should not be subjected to stress or be given any immune-suppressant drugs as these can precipitate the disease in carriers.

Treatment of cats with signs of the disease is invariably fruitless as death usually occurs within a matter of months. When it is given treatment is aimed at reducing immune-complex formation and remission and rarely total recovery have been reported following the use immunosuppressive and anti-inflammatory drugs (often in combination)  including :

An intranasal vaccine has been developed and it is available in many countries. It's efficacy is believed to be 50-75% . The vaccine will not be as effective if it is given to cats that have already been exposed to the virus - so blood testing for the presence of antibodies pre-vaccination is recommended.

The prognosis is poor for cats showing signs of the disease


Updated October 2013