All about FIP
(Feline Infectious Peritonitis)

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


Up to 9 out of 10 cats carry a harmless feline coronavirus FCoV.

Most cats are asymptomatic.

FCoV is spread easily between cats via faeces and the use of shared litter trays and grooming etc. FCoV can also be spread in saliva.

Most cats become infected in multi-cat setups.

Most kittens become infected at several weeks old when their maternal antibodies wane.

Most kittens have robust immune systems which eliminate FCoV.

Some cats can become chronic shedders of FCoV eg in faeces.
Due to the nature of the shedding and infection process, the cycle of having FCoV can be difficult to break.

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

A small percentage of FCoV infected cats get Feline Infectious Peritonitis (FIP.)

This occurs in cats commonly with a history of a perfect storm of stressors eg vaccines, neuter, rehome, specific breeds are more susceptible, male, pedigree, under 2 etc. We know stress impacts the immune system. Ultimately FIP is due to a compromised immune system.

In the process of a cat developing FIP, the enteric FCoV which lives in most cats’ guts (without issue,) escapes the bowel and enters the bloodstream.

A cat’s blood can be tested and show FCoV antibodies.
This does not mean the cat has FIP or will develop FIP.
In cats who develop FIP, the FCoV in the blood stream enters cells called macrophages. In a cat with a robust immune system these macrophages 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 (ie over-reaction with an inflammatory response) that determines FIP development.

In cats that develop FIP (where the cat’s immune system and its macrophages cannot overcome the FCoV to FIP mutation) the cat’s body responds with an inflammatory response.

This is evidenced in Wet FIP cats with fluid effusions accumulating in cavities e.g. chest and abdomen.
Dry FIP cats can get pyogranulomatous lesions (which have been viewed most commonly post-mortem prior to successful treatment existing) in organs eg liver and kidneys.
Other inflammatory responses include uveitis of the eyes and other ocular symptoms ie Ocular FIP and also neurological symptoms ie Neurological FIP.

Owners can test their cats for FCoV shedding in faeces at Glasgow University Vet Diagnostic Services. The result is neither prognostic or diagnostic of FIP. The results explain how much FCoV is being shed, if any.

By testing blood for FCoV antibodies the same applies in that it is neither diagnostic or prognostic of FIP but the test will confirm
if the cat has been infected with FCoV and if it is a recent infection.

Information about FCoV testing can be found on our Information Page

FIP Symptoms

FIP Symptom Videos

Neuro FIP Example

Wet FIP Example (Contributed by A. Lambrecht)

Abdominal fluid removal – must be done with extra caution as it removes lots of protein from the body suddenly (the Wet FIP cat may eat ravenously to replenish its proteins which are taken by the FIP effusion. It is vital they are fed high protein food to help them.)

Chest fluid removal – is essential when the cat has difficulty breathing.

Gilead Sciences and Explanation of Legal and Illegal FIP Treatments