Feline Infectious Peritonitis in Cats

Signs, Diagnosis and Treatment of FIP

Closeup of a cat's face
" Cat?" ( CC BY 2.0) by  aymen_bet

Feline infectious peritonitis is a viral disease of cats seen worldwide. Not all cats infected with the virus causing FIP will become ill, but cats who do develop signs of FIP will likely succumb to the disease eventually.


FIP is a complex disease. FIP is a result of infection with feline coronavirus -- but while large numbers of cats are infected with feline coronavirus, few will ever develop FIP.

FIP is thought to result from a mutation of the virus within the body, combined with the response of the immune system, leading to inflammation in various organ systems. The mutated virus is not shed by the cat, so FIP is not actually contagious, though the more benign feline coronavirus is contagious.

Risk Factors

FIP is most often seen in young cats, less than 3 years old, but it can be seen at any age. It is thought that the mutation in the virus that leads to FIP is more common in cats with immature or weakened immune systems.

The coronavirus is spread through direct contact via the nose and mouth with infected feces, so sharing litter boxes is a major route of transmission of coronavirus. However, as previously noted, FIP only develops in some cats who are infected with the coronavirus, so exposure does not automatically mean cats will get FIP.

Signs and Symptoms of FIP

There are two main categories of FIP: the wet form and the dry form, which have different characteristics.

These broad forms are not necessarily completely distinct, however, and some cats will have some of both.

Wet Form

  • distention of abdomen due to fluid build up
  • difficulty breathing due to lung involvement
  • fever (long term, unresponsive to treatment)
  • loss of appetite
  • weight loss
  • depression

Dry Form

  • fever (long term, unresponsive to treatment)
  • loss of appetite
  • depression
  • weight loss
  • variable other signs related to organ failure, depending on which organs are involved (commonly involves kidneys, liver, pancreas, nervous system, eyes)

Diagnosis of FIP

Confirming a diagnosis of FIP can actually be very difficult. The best method to confirm a diagnosis involved examining tissue samples from biopsies microscopically, including special tests to mark the presence of the virus in tissue samples.

If these tests are not possible, 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 sampled from the abdomen if the wet form is present.

Testing for antibodies to coronavirus is not helpful in the diagnosis of FIP but is useful in screening healthy cats before introducing them to a coronavirus-free cat or group. However, a positive result only indicates exposure to coronavirus and possible shedding of coronavirus but does not mean a cat has, or will develop FIP.

Treating FIP

There is no treatment for FIP. Some supportive measures, including draining excessive fluid build-ups can provide temporary relief. A variety of medications designed to reduce the abnormal immune response to the virus or reduce the ability of the virus to reproduce have been tried and may provide some relief from the disease.

Generally, cats with the wet form succumb to FIP sooner (days to weeks) than those with the dry form (few months), though survival for several months may be possible.

Preventing FIP

Preventing exposure to coronavirus is the best way to prevent FIP. Keeping cats indoors offers protection, as well as only bringing coronavirus-negative cats into the household.

There is a vaccine available, although its use is controversial. The vaccine is given in the nose and is designed to produce just a local response to prevent the virus from gaining access to the body. The vaccine is not 100 percent effective and must be given before natural exposure to coronavirus to be effective.

Because FIP is quite uncommon in the general cat population, the need for routine use of FIP vaccines is uncertain. Your vet can discuss the use of FIP vaccines in your cat.

The Multi-Cat Household

Housemates of a cat diagnosed with FIP do not have a greater risk of developing FIP, unless they are litter mates that share a genetic predisposition. They have also likely been exposed to coronavirus already, so no special precautions are usually necessary. Your vet can provide further advice regarding home care.

Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.