Causes and Types of Feline Infectious Peritonitis

Kelly Roper
Sick cat at vet

Feline infectious peritonitis (FIP) is a fatal, viral disease that currently has no cure. Depending on the form it takes, it affects the functions of a cat's vital organs, eventually leading to the animal's death. While nearly any cat is at risk of developing FIP, there are some common risk factors to be aware of.

Causes of FIP

According to the Cornell University College of Veterinary Medicine (CUCVM), feline infectious peritonitis is caused by feline coronavirus. For reasons that have yet to be determined, either the coronavirus mutates or something goes wrong with the typical immune response to the original coronavirus, resulting in production of the FIP virus. The virus is then transported throughout a cat's body via infected white cells.

FIP Forms and Symptoms

FIP takes one of two basic forms, wet or dry. Both forms produce general symptoms such as:

  • Persistent fever
  • Lethargy
  • Lack of appetite resulting in weight loss
  • A generally unkempt look

Beyond those signs, each form of the virus produces its own specific symptoms.

Wet Form

Potbelly cat

Wet FIP produces fluid in the abdomen and/or chest. Symptoms include:

  • The cat develops a swollen (fluid-filled) abdomen.
  • The animal displays labored breathing, which is caused by the fluid buildup.

Dry Form

Dry FIP produces granulomas which can form in various organs, so the symptoms shown depend on which organ(s) are affected. For example:

  • Kidneys: The cat is constantly thirsty and urinates a lot.
  • Liver: The cat develops jaundice.
  • Eyes: The eyes become inflamed.

Testing and Diagnosing the Virus

According to Wendy C. Brooks, DVM, DipABVP, diagnosing FIP can be particularly difficult because the outward symptoms are common to a number of diseases. There is no definitive test for FIP at this time, so veterinarians usually test an affected cat for prior exposure to coronavirus (FIP titer) to see if the results will support a diagnosis of FIP when combined with the cat's symptoms.

Other tests that may be used toward a cumulative diagnosis include, but are not limited to:

  • Albumin to globulin ratio: Globulin levels tend to go up with FIP, while albumin levels tend to go down.
  • Serum protein levels: These levels are typically high in cats that have FIP.
  • Tissue biopsy: This test is rarely used since most cats with FIP aren't good candidates for the procedure. A tissue sample is stained to look for the presence of coronavirus, and there will only be enough evidence of that virus if the cat has FIP.

Treating an FIP-Positive Cat

Recovering cat

There is no cure for FIP, so treatment usually consists of making an affected cat as comfortable as possible. This includes treating individual symptoms, but the disease worsens regardless, and the cat will either die on its own or be humanely euthanized.

According to CUCVM, veterinarians sometimes treat cats with:

  • Corticosteroids to repress the immune response and reduce inflammation
  • Cytotoxic (anti-cancer) drugs
  • Antibiotics to treat secondary infections

Supportive care may also include such measures as:

  • Providing excellent nutrition, as well as antioxidants
  • Administering IV fluid therapy to stave off dehydration
  • Draining fluid buildup caused by wet FIP
  • Blood transfusions if the cat develops anemia

Risk Factors for FIP

Dr. Pedersen lists several risk factors that increase a cat's chance of getting FIP.

  • Overcrowding cats, such as what sometimes happens in shelters, catteries, and multi-cat households, increases the risk for FIP due to the likely increased exposure to coronavirus.
  • Unclean conditions, which contribute to more coronavirus in the cats' environment and, therefore, greater risk that one or more cats will develop FIP.
  • Genetic inheritance is also a factor since the disease appears more frequently in certain breeds, such as Birman and Burmese cats, as well as certain bloodlines.

FIP Is Not Contagious

According to Dr. Brooks, even though coronavirus is contagious, the FIP virus that develops from the coronavirus is not contagious because cats don't shed it into their environments. The virus is also not contagious to humans or dogs.

Preventing FIP

The FIP Vaccine

According to the ASPCA, there is an intranasal vaccine for FIP, but it's not recommend by the American Association of Feline practitioners since it's only effective on cats that test negative for coronavirus antibodies at the time of vaccination. Since coronavirus is so common, many kittens are exposed to it before they are old enough to be vaccinated, which would render the vaccine useless.

Additional Preventative Measures

Currently, the best prevention is limiting a cat's exposure to coronavirus. CUCVM recommends:

  • Providing proper nutrition
  • Keeping vaccinations up to date
  • Scooping litter boxes frequently
  • Keeping litter boxes far away from food and water dishes
  • Avoiding overcrowding

The Search for a Cure

Although a cure has been elusive so far, ongoing research by UC Davis and other organizations may one day produce a more effective vaccine, as well as medications that could slow down the virus. With a lot of work and a little luck, FIP may one day become a threat of the past.

Causes and Types of Feline Infectious Peritonitis