What is FIP and why does FIP happen in some cats?

FIP stands for Feline Infectious Peritonitis

FIP IS NOT CONTAGIOUS! Infectious means caused by an infection. Contagious means that it spreads from one individual to another. The disease FIP does not spread between cats.

Feline Coronavirus (FCoV) is very very common and mostly harmless. Up to 9 out of 10 cats carry a harmless feline coronavirus FCoV and they are mostly without any symptoms. Occasionally at first infection cats will get a mild episode of diarrhoea. FCoV is spread easily between cats via faeces and saliva and the use of shared litter trays, bowls and mutual grooming. Most cats become infected in multi-cat setups.

Kittens and FCoV

Most kittens become infected at several weeks old when their maternal antibodies wane but their immune systems eradicate the infection. Some cats can become chronic shedders of FCoV for example in their faeces. Due to the nature of the shedding and infection process, the cycle of having FCoV can be difficult to break especially in breeding households.

Control and Eradication

FCoV can be only be eradicated in multi-cat households by rigorous hygiene, monitoring tests to record which cat is shedding FCoV in faeces and ultimately by ensuring cats have robust immune systems.

FCoV testing

A cat’s blood can be tested and show FCoV antibodies.This does not mean the cat has FIP or will develop FIP. All it means is that the cat has been exposed to FCoV, like the majority of cats are. Faeces can also be tested for FCoV. Testing for FCoV is not really helpful in diagnosing FIP. Neither does it help predict outcome of FIP cases.
In cats which develop FIP, the FCoV mutates and enters the blood stream. In a cat with a robust immune system, macrophage cells in the blood and tissues would work to overcome the infection.
The FCoV is changing all the time and mutating in the cat. It is this process and the cat’s immune response to it (i.e. over-reaction with an inflammatory response) that determines FIP development.

From FCoV to FIP

A small percentage of FCoV infected cats get Feline Infectious Peritonitis (FIP.) For this to happen, the virus must mutate within the cat, escape the bowel and enter the cat’s bloodstream. Furthermore the cat’s immune system must react with this mutated virus to cause an inflammatory response and hence the disease. This can follow stressful events such as vaccination, neutering, transport, rehoming and surgery. Specific breeds are more susceptible as are younger and male cats.

FIP clinical signs

Some cats develop fluid effusions in the chest or abdomen, which can cause laboured breathing or a potbellied appearance. This is termed Wet FIP. Dry FIP cats can get pyogranulomatous lesions (which have been viewed most commonly post-mortem prior to successful treatment existing) in organs such as the liver, kidneys, eyes and brain. These can result in organ dysfunction, altered blood tests, nervous system dysfunction and visible changes in the eyes, such as uveitis (inflammation of the iris). These changes can be described as Ocular FIP (eye disease) and Neurological FIP (brain and spinal cord disease). In truth the reaction to the virus is not always so clear cut and in any one case there may be features of more than one or even all of these forms.

Reaching a diagnosis

There are a variety of testing methods to support a diagnosis of FIP and this can be very complicated. Helping you understand how the various tests are used and how they fit in with your cat’s history and clinical signs is part of our role at FIP Support UK. This is helpful prior to diagnosis as well as whilst monitoring treatment or prevention strategies.