Feline Infectious Peritonitis

What is feline infectious peritonitis?

Feline infectious peritonitis (FIP) is an uncommon but fatal disease of cats caused by a virus called a feline coronavirus (FECV). It is a particularly devastating disease because it is fatal, there is no known cure and it mainly affects young cats (less than 2 years old). FECV causes little or no clinical signs in cats and are spread easily; therefore most cats are infected at some stage in their lives. FIP is a disease where the FECV mutates in a particular cat and the cat’s immune system mounts a response that results in a severe inflammatory response that can be controlled. This results in inflammation of blood vessels and fluid build up in the abdomen or chest or ‘granulomas’ in organs that affects their function leading to organ failure.

How does a cat become infected with FECV?

Coronaviruses can be transmitted between cats through a faecal-oral route such as sharing litter trays, food bowls, and grooming each other. This commonly occurs during kittening and therefore many kittens become infected from the queen at a very early age. Some cats may develop FIP years after being infected with a FECV as the virus can lay dormant within the body.

What clinical signs does a cat infected with FIP develop?

The first signs of FIP may be very vague: dullness, lethargy, and inappetance are common findings. After a period of several days or a few weeks other signs will develop. Most commonly this involves the accumulation of fluid in the abdomen or chest leading to a swollen abdomen or difficulty breathing. In some cats, little or no fluid accumulates, but the virus may cause inflammation in the eye, brain, or other organs of the body leading to clinical signs depending where the virus has spread. Once clinical signs develop, most cats deteriorate rapidly, although some remain quite bright for several weeks. Sadly the disease always progresses and eventually results in death.

How can FIP be diagnosed?

Unfortunately, FIP is particularly difficult to diagnose and veterinarians have to rely on a variety of tests to confirm FIP. Although many tests can give us a good clue of a diagnosis of FIP the only test currently able to confirm this disease is a biopsy of the affected organ. Many cats are too ill to perform a biopsy and in these cases your veterinarian may only be able to give you a strong indication that your cat has FIP. Blood tests often show mild anaemia, subtle changes in white blood cell counts, and often a high ‘globulin’ or antibody reading.

Your veterinarian may suggest a radiography or ultrasound to check for fluid in the chest or abdomen and then obtain a sample of this fluid, which often has very specific characteristics of FIP or at least rules out other diseases that can cause fluid build up in these body cavities such as cancers and heart failure. Your veterinarian may suggest a test that looks for viral particles in the fluid (immunofluorescence) and whilst this is a useful test it is not always 100% definitive.

Another blood test that is commonly performed is to look for antibodies against FECV virus (‘coronavirus serology’). It is important to understand that this test has severe limitations, as a positive result only means that a cat has been exposed to a coronavirus and NOT necessarily the FIP specific form. The test is not able to provide a diagnosis of FIP - many perfectly healthy cats will have positive test results and never develop FIP.

Currently the only way to make sure of the diagnosis of FIP is by histological examination of affected tissue (or by post-mortem examination) by a pathologist at a laboratory. If there is any doubt about the diagnosis a biopsy may be suggested by the veterinarian so that FIP can be distinguished from another, perhaps treatable, disease. 

In the future more reliable diagnostic tests based on blood samples rather than the need for a biopsy may become available.

Is there any treatment for FIP?

FIP is a fatal illness, and essentially all cats that develop clinical signs will go on to die of the disease. At best veterinarians can offer only palliative care with medication to reduce the inflammatory response (corticosteroids and other drugs) or to stimulate the immune system to try to fight the infection more effectively, such as interferon. A cat specific interferon is available and is given by injection; it will sometimes give temporary remission of clinical signs but is relatively expensive and may not work in all cases. In many cats, once a diagnosis has been made euthanasia is often the most humane and appropriate course of action.

How can disease be prevented?

Control of FIP is very difficult. There is currently no vaccination available against FIP in Australia. There is a vaccination available in some countries, however it may not be effective in preventing the disease. In breeding situations, FIP has been effectively controlled by strict hygiene and early weaning practices thereby producing kittens free of coronavirus infection; however, if they have contact with other cats in their new environment they may contract the disease then.

If FIP is diagnosed in a multicat household, it is sensible not to introduce any new cats into the house for at least three months. Similarly if the cat came from a single-cat household, although the virus is not likely to survive long in the environment, it is probably sensible not to introduce a new cat into the house for a period of 1-2 months to try and avoid any potential exposure to the virus. Although one cat in a household may develop FIP, this fatal form of the FECV is not thought to be transmitted and therefore your other cats are very unlikely to develop FIP.