Home > Related Diseases > Feline Infectious Peritonitis
Overview
- Feline infectious peritonitis, or FIP, is a rare disease that may develop in some cats infected with the coronavirus.
- It is difficult to treat, though a recent new treatment, GS-441524, appears to be helping some cats.
- One of the main problems with FIP is that it is very difficult to diagnose definitively. This page explains about the possible methods of diagnosis (which tend to vary depending upon whether you are dealing with wet or dry FIP) and possible treatments.
What is Feline Infectious Peritonitis?
Feline infectious peritonitis is an illness that develops in a small number of cats after they have caught a type of virus known as the coronavirus, which then mutates into FIP.
The coronavirus itself (which, like other viruses, has many strains) is relatively common in cats, with about 80% exposed to it. What is important to grasp is that only certain strains of the coronavirus can mutate into FIP. Most cats with the coronavirus have been exposed to feline enteric coronavirus (FECV).
In theory, the coronavirus can mutate in any cat, but in practice most cats with coronavirus make a full recovery (though some may be carriers), with only about 5-10% of cats exposed to the coronavirus going on to develop FIP.
After the cat is exposed to a virus, the cat’s body attempts to develop antibodies to it to fight off the virus. In most cases, these antibodies will successfully fight off the virus, but if the cat develops FIP, this mechanism can actually work against the cat, with the FIP virus being carried around the body. Commonly affected areas include the brain, the kidneys or the abdomen (in Lily’s case, the abdomen was affected).
There are two forms of FIP:
- effusive (wet)
- non-effusive (dry)
Wet FIP used to be considered harder to treat, though a newer treatment is proving very promising (see below).
How Feline Infectious Peritonitis Is Transmitted
In principle, cats with feline coronavirus can infect other cats with the coronavirus. This does not necessarily mean the other cats will go on to develop FIP, but it is a possibility.
The corona virus may be transmitted via faeces or saliva while a cat is actively infected with the coronavirus.
However, the most common route of transmission is from a mother cat to her kittens, usually when the kittens are aged 5-8 weeks.
Risk Factors
Weaker Immune System
FIP commonly affects cats with weaker immune systems, including:
- kittens and young cats (most cats with FIP are under the age of two)
- mature cats
- cats who have feline leukaemia
Multicat Environments
FIP is more common in cats who live in catteries, shelters, or with a number of other cats. It is very rare in cats who live alone or who live outside.
Cat Virus is the website of Dr Addie, a lecturer in veterinary virology and an expert on FIP. Her site is available in a number of different languages.
Breed
Some breeds appear to be more susceptible to FIP
Cornell University College of Veterinary Medicine has a good overview.
The Winn Feline Foundation has information about FIP.
Newman Veterinary has information on FIP.
How FIP Develops
In a small number of cats, the particular strain of coronavirus which has infected the cat will mutate and develop into FIP. After the cat is exposed to a virus, the cat’s body attempts to develop antibodies to it to fight off the virus. In most cases, these antibodies will successfully fight off the virus, but if the cat develops FIP, this mechanism can actually work against the cat, with the FIP virus being carried around the body. Commonly affected areas include the brain, the kidneys or the abdomen (in Lily’s case, the abdomen was affected).
Very few cats on Tanya’s Feline CKD Support Group have FIP, but I’ve had three CKD cats and one PKD cat, and fate decided I needed to experience FIP too. I lost the most adorable kitten in the world, Lily (left) to dry FIP. You think CKD is bad? Well, FIP is worse, because there is so little you can do for it and so little hope, though there is a promising treatment for wet FIP now available.
Symptoms
Symptoms of FIP include poor growth in kittens (an affected kitten is often much smaller than his/her littermates, which was certainly the case for Lily). Cats with the wet form of FIP often have ascites (fluid build up in the abdomen). Cats with the dry form may develop other symptoms, depending upon the area affected in the body. Commonly affected areas are the eyes, brain, abdomen and kidneys. Cats whose kidneys are affected may develop enlarged kidneys and CKD.
Other possible symptoms include a chronic fever (and accompanying raised temperature) which does not respond to antibiotics, loss of appetite, weight loss and lethargy.
Cats with wet FIP usually have fluid build up (hence “wet”) so possible symptoms include ascites.
Diagnosis
Diagnosing FIP is notoriously difficult. There is no one test to diagnose it; instead, vets look at a variety of diagnostic tests and the cat’s symptoms in order to make a diagnosis.
Possible signs in bloodwork include elevated neutrophils and elevated total protein. You will usually see a low albumin:globulin ratio combined with very high globulin levels. An A:G ratio below 0.4 combined with elevated globulins, indicates that FIP is quite likely, assuming other causes of a low A:G ratio have been ruled out,
Although it is hard to diagnose FIP, it is worth noting that an A:G ratio over 0.8 rules out FIP.
Because FIP is so difficult to diagnose, many people use the extremely helpful algorithm created by Dr Diane Addie, an eminent virologist, which can be found here:
http://www.catvirus.com/downloads/FIPdiagnosisalgorithm.pdf
Treatments
This page last updated: 04 October 2025
Links on this page last checked: 12 December 2017