Feline Infectious Peritonitis

FIP, or Feline Infectious Peritonitis, is caused by Feline Coronavirus

Sadly, every year we see a few challenging cases of this severe, debilitating, and potentially fatal cat disease. 

FIP, or Feline Infectious Peritonitis, is caused by Feline Coronavirus.  

It is important to note that the coronaviruses affecting cats are very different from the coronavirus which causes COVID-19 in people. The coronaviruses that affect cats (called feline coronaviruses, or FCoV) are alpha-coronaviruses, and the current SARS-Cov-2 coronavirus which causes COVID-19 in people is a beta-coronavirus. These are different diseases, which occur in different species caused by different types of coronaviruses.  

The virus causing feline coronavirus does not affect people or dogs. 

Infection with Feline coronavirus is actually quite common in cats. Most of the time it does not cause any problems at all, other than perhaps a mild, self-limiting diarrhoea, as it replicates in the cells of the cat’s gut lining.  

Although infection can occur in cats of any age, it is most often seen in young cats, and young, pure-breed cats are definitely much more at risk, with some pure-breeds being more predilected.  Around 80% of cases diagnosed are in cats less than 2 years old, and many cases are kittens around 4-12 months old. 

About 25% of pet cats have been, or are exposed to this virus, however this number goes up to over 80% in any multi-cat households. and may reach 100% in any larger cat “colonies”. 

Sadly, young kittens may arrive at a new home already infected with this virus.

Most cats, once infected, are a bit quiet and have diarrhoea for a few days, but then they recover. In the meantime, however, they have already shed the virus, mainly in their faeces, to any other cat that may have been in contact with their faeces. The virus shed in faeces may survive in the environment for several days or weeks and infection is caused when another cat then ingests the virus, through cleaning faeces from their fur. 

Infected cats usually mount an immune response producing antibodies against the virus. This immune response means that these cats never develop the disease. 

In approximately 10 percent of cats though, one or more mutations of the virus can alter its biological behaviour, resulting in white blood cells, becoming infected with the virus, and then spreading it throughout the cat’s body. The virus then no longer replicates in the gut lining, but instead it then attacks the infected cat’s own immune system and blood vessels. This is then called Feline Infectious Peritonitis, FIP, and is now a much more concerning and serious disease. 

With FIP an intense inflammatory reaction occurs around vessels in the tissues where these infected cells locate, often in the abdomen, kidneys, or brain. It is the interaction between the body’s own immune system and the virus that is responsible for the development of this disease. 

Without a good immune response an infected cat will go on to develop the clinical signs of FIP.  These signs can be vague and non-specific, typically lethargy, loss of appetite and a persistent fever. If the cat’s immune system cannot clear the virus at this stage, the condition will progress to one of the two main forms of the disease:  

Wet FIP (also known as Effusive FIP). Characterised by damage to and severe inflammation of blood vessels, so that they leak fluid. This can cause fluid build-up and inflammation within body cavities. Sadly, these cases generally deteriorate rapidly. 

Or Dry FIP (also known as Non-Effusive FIP). This occurs when the immune system can slow down the replication of the virus, but not stop it completely. It is characterised by a chronic inflammation of blood vessels within the body organs causing inflammation of the eyes, brain, and other organs. The type of changes present is usually what is known as ‘pyogranulomatous’ inflammation. 

The best test to confirm a diagnosis of FIP is to collect a biopsy from any affected tissues. Typical FIP-type inflammation is usually seen, and the diagnosis can be confirmed using a Laboratory technique called ‘immunohistochemistry’ which will demonstrate the presence of the virus itself within the damaged tissues. If taking a tissue biopsy is not possible due to deteriorating health, the diagnosis must be made on a combination of other factors, including clinical signs and laboratory tests which can include blood tests and analysis of fluid samples, if the wet form is present. 

Sadly, as yet, there is no cure for FIP, and there is no vaccine available in the UK against the Feline Coronavirus.

Anti-inflammatory drugs and nursing may improve the cat’s quality of life during the chronic disease process.  

Good hygiene and avoiding overcrowding are essential strategies for minimising the risk of FIP. Sharing litter boxes is a major route of transmission of coronavirus between cats, but thankfully, the virus is readily destroyed by common, cat-friendly disinfectants. Have at least one litter box for every two cats in the home and locate these in easy to keep and clean areas. Keep all litterboxes away from food and water bowls, and disinfectant them thoroughly daily.  

The best prevention is to keep cats in much smaller, stable groups and practise good daily hygiene to minimise the spread of the virus.  Avoiding stress is also advised, maintaining a good nutrition with a suitable diet to promote a healthy, strong immune system, and regular ongoing preventive healthcare treatments for all cats in the household. 

If you are concerned about any of the symptoms described in your cat, please contact your Vet Practice for an appointment for a full clinical examination.


Alison M Laurie-Chalmers 

Senior Consultant, 

Crown Vets. 

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