Feline Infectious Peritonitis in Cats

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

Feline infectious peritonitis is a viral disease of cats that is seen worldwide. Most cats infected with the virus causing FIP will never become ill, but cats who do develop signs of FIP will always succumb to the disease. There are two forms of the disease: wet form and dry form. They are equally tricky to diagnose.

What Is FIP?

FIP is a complex disease that is a result of infection with the feline coronavirus. 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 that combines with the response of the immune system. This combination leads to inflammation in various organ systems. The mutated virus is not shed by the cat, so while FIP is not actually contagious, the more benign feline coronavirus is contagious to other felines. It is not contagious to dogs or humans.

Signs and Symptoms of FIP

The two main categories of FIP, the wet form and the dry form, have different characteristics. These broad forms are not necessarily completely distinct and some cats will have some of both.

Common symptoms of the wet form of FIP include:

  • 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

Common symptoms of the dry form of FIP include:

  • 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, nervous system, eyes)

Causes of FIP

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. Most cats that develop FIP have been recently exposed to some sort of stressful experience such as boarding, rehoming, or surgery. The coronavirus is spread through direct contact via the nose and mouth with infected feces. Sharing litter boxes is a major route of transmission of coronavirus between cats. FIP only develops in some cats who are infected with the coronavirus, so exposure does not automatically mean cats will get FIP.

How Is FIP Diagnosed?

Confirming a diagnosis of FIP can actually be very difficult. The best method to confirm a diagnosis of FIP requires a veterinarian taking a biopsy. The tissue samples from the biopsy are examined microscopically and often include 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. A positive result only indicates exposure to coronavirus and possible shedding of coronavirus but does not mean a cat has or will develop FIP.

Treatment

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

How to Prevent FIP

Preventing exposure to coronavirus is the best way to prevent FIP, however this is very difficult to do as up to 80-90% of cats are infected with the virus.

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 efficacy of the vaccine is questionable and it 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 generally not recommended, although it can sometimes be used in shelters where the risk is highest. Your vet can discuss the use of FIP vaccines for 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.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.