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..

Cause

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

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

Diagnosis
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.

Treatment
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.

Prevention
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.

Around 1 cat in 10 who is infected with FCoV develops FIP. Very often after one cat has died of FIP there is a second cat in the household which is known to be infected, but is perfectly healthy. There are currently no drugs which can prevent a FCoV infected cat developing FIP, but there are a number of other ways we can help our cats to deal with the infection:
 

Minimise the cat's stress

It has been shown that most cats who have developed FIP experienced stress before they developed FIP. Cats with wet (effusive) FIP are frequently stressed 2-4 weeks before they develop FIP, cats with dry (non-effusive) FIP experience the stress up to a year before they get sick. It is therefore wise not to stress cats which have FCoV antibodies if at all possible - for example, don't rehome them; delay having them neutered or any other operation which is not life-saving; if you have to leave them, get somebody to look after them in their home rather than putting them into a cattery.

Examples of situations which cats find stressful:

being rehomed
moving house
 new additions to house: baby, dog, cat, kitten
 too many cats in one house
 going into cattery
surgery (being neutered, getting a dental)
trauma (e.g. road accident)
intercurrent illness
pregnancy, parturition, lactation