FIP (Feline Infectious Peritonitis)

FIP (Feline Infectious Peritonitis)

Animals Affected



Feline infectious peritonitis, or FIP, is a poorly understood and extremely dangerous disease of cats.  The disease is resistant to treatment and very difficult to diagnose. Almost all cats that contract FIP die from the disease.

FIP is caused by a mutated form of coronavirus.  The non-mutated form of feline coronavirus is extremely common and causes mild gastrointestinal symptoms (such as diarrhea) or respiratory symptoms (such as sneezing or coughing).  Rarely, feline coronavirus mutates, or changes, into an extremely aggressive virus that causes FIP.  The FIP virus causes inflammation (irritation) of multiple organ systems, and is nearly 100% fatal.

As its name implies, FIP is theoretically contagious.  However, outside of cattery and shelter environments FIP does not frequently spread among cats living within a household.  Many experts believe that, rather than spreading contagiously among cats, most cases of FIP are the result of unique mutations of the normally mild feline coronavirus within the affected cats.


Symptoms of FIP often are vague.  There are no symptoms that are unique to the syndrome, and there are no symptoms that occur in 100% of cats with FIP.

  • Weight loss is the most consistent symptom of FIP.   A noticeably poor appetite may be present.
  • Cats suffering from FIP may be lethargic.  However, lethargy is not universal in the syndrome.
  • Kittens with FIP usually fail to grow as they should.
  • FIP may cause respiratory problems including sneezing, coughing, nasal discharge, or difficulty breathing.
  • An unkempt hair coat may occur in cats with FIP.
  • FIP may cause the affected cat’s abdomen to become swollen and distended.
  • Vomiting or diarrhea may occur in cats with FIP.
  • Cats with FIP may develop a yellow coloration to their eyes, skin, and gums known as jaundice.
  • Rarely, neurological symptoms including personality changes, confusion, staggering, or seizures may occur.

Risk Factors and Prevention

  • FIP occurs most often in cats less than five years of age.  Kittens less than a year old are at the highest risk.
  • FIP is most common in catteries, shelters, and other environments in which multiple cats are housed.
  • Stress may contribute to the development of FIP.  Stress due to overcrowding of cats appears to be especially dangerous.
  • Cats and kittens that recently have been adopted from shelters or catteries are at increased risk of developing FIP.
  • Poor nutrition and poor hygiene contribute to the development and spread of the syndrome.  Failure to keep litter boxes clean is considered to be a leading risk factor for spread of the disease among cats.
  • Cats that are infected with other diseases, such as feline leukemia, are at increased risk of developing FIP.
  • Purebred cats appear to be at higher risk for FIP than cats that are not purebred. This may be due to inbreeding, or due to the fact that most purebred cats come from catteries.
  • A vaccine for FIP (Primucell®, made by Pfizer) is available.  The efficacy of the vaccine is debated among experts, and the vaccine is not widely used.


  • The vast majority of cats that develop FIP die from the disease.
  • FIP may spread from cat to cat.  However, this is not common outside of catteries, shelters, and households in which more than 6 cats live.


Definitively diagnosing FIP is challenging.  No simple or readily available blood test or assay can diagnose the syndrome with 100% certainty.   Most diagnoses are not conclusive and are based upon a combination of symptoms and multiple irregularities in a wide variety of blood tests, urine tests, diagnostic imaging evaluations (X-rays and ultrasound), and tests of other bodily fluids.

  • Blood tests for antibodies to coronavirus are available.  These tests, called titers, are of very limited usefulness in diagnosing FIP because they do not differentiate between FIP and the more benign and common non-mutated form of coronavirus.
  • Biopsy of affected organs, combined with special microscopic evaluation of the tissues (called immunoperoxidase staining), is considered the most definitive method of diagnosing FIP.  This form of testing is rarely performed in practice because it is invasive and expensive.
  • FIP also can be diagnosed by testing a specific type of body fluid (called effusion) with an analytical method known as PCR.  This is not possible in all cases of FIP, because effusion is not always present.


Treatment options for FIP are limited.  Although a very wide variety of treatments have been explored and evaluated, none can cure the disease.  Most treatments are aimed at extending lifespan and improving quality of life.   These treatments do not consistently prevent a fatal outcome.

The most commonly used treatments include medications related to prednisone, in combination with nursing care and nutritional support.  Compounds that modulate the response of the immune system may help to palliate the effects of the disease.  Of these, alpha-interferon appears to be one of the most promising.


Although spread of the virus is not common in most household situations, owners of cats that have died from FIP should take steps to prevent spread of the disease to other cats in the house.  The house should be thoroughly cleansed, and special attention should be paid to litter boxes.  Most household cleansers inactivate the virus.

Experts estimate that coronaviruses can survive for seven weeks outside of the body. Households that have lost a cat to FIP should wait a minimum of seven weeks before adopting a new cat.


Coronaviruses are very common in many different species.   In people, sudden acute respiratory syndrome, or SARS, is caused by a coronavirus.  In dogs, a coronavirus is a common cause of diarrhea.  However, coronaviruses do not appear to spread between cats, dogs, and humans.  FIP does not appear to pose a health threat to dogs or people.

Many sources provide detailed and complicated methods for diagnosing FIP based on coronavirus titers.  Most experts agree that these methods are not reliable, and that coronavirus titers are of very limited use in the diagnosis of FIP.

Copyright © Eric Barchas, DVM. All rights reserved.
The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.