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Summary
Feline infectious peritonitis, also known as FIP, is a deadly viral disease of cats. The virus that causes FIP is a mutated form of feline coronavirus. Feline coronavirus is not the same virus as the novel coronavirus, also known as COVID-19, that infects humans.
Feline coronavirus is a highly contagious virus, and up to 90% of cats in multi-cat households and 50% of cats in single-cat households become infected. However, most infected cats do not have symptoms or develop any issues from feline coronavirus infection. Occasionally, some cats develop short-term diarrhea or loose stools. The virus is spread mostly through sharing litter pans and accidental ingestion of feces.
In some infected cats, feline coronavirus will mutate in the cat's body, to become feline infectious peritonitis virus. This form of virus causes disease in many organs and the blood stream. It causes a widespread, overreactive immune system response, leading to inflammation and severe tissue damage. Almost all cats that develop FIP die. Fortunately, only about 5% of cats exposed to feline coronavirus develop FIP infection.
Symptoms and Identification
Two types of FIP occur, although sometimes they are seen together. The effusive or "wet" form and the noneffusive or "dry" form.
The wet form of FIP results in fluid retention, leakage of fluid from blood vessels, and associated symptoms. Fluid builds up in the belly, inside the chest cavity, and sometimes in the space surrounding the heart (i.e. pericardial sac). Symptoms include:
Acting very tired (lethargy)
Poor appetite
Fever
Weight loss
Trouble breathing
An unusually large belly
The dry form possibly occurs because the cat was able to fight the FIP virus to a degree. The vessel leakage and fluid retention does not occur, but inflammation throughout the body causes many of the organs to work improperly or fail. The kidneys, brain, lymph nodes, eyes, and gastrointestinal (GI) tract tend to be most affected. Symptoms of the dry form include:
Acting tired
Poor appetite
Fever
Weight loss
Trouble breathing
Blindness
Falling over and trouble walking
Tremors
Paralysis
Head tilt
Vomiting or throwing up
Loose stools
To diagnose FIP, veterinarians will run tests on a cat's blood to assess the immune system, the bone marrow response, and to see how the internal organs are handling the disease (complete blood count/CBC, chemistry panel).
If abdominal fluid is present, the vet will also run tests on the fluid. Sometimes X-rays and abdominal ultrasound are needed to determine how severe the disease is and to cross other potential diseases off the list of concerns.
While these tests give the veterinarian a strong suspicion for FIP, especially in wet form cases, the answer is not always clear. To officially diagnose FIP, a biopsy must be performed on tissues most affected by the disease. Fortunately, an official answer isn't always necessary if the symptoms and other tests indicate a strong diagnosis for FIP.
Affected Breeds
According to some scientific studies, FIP is more likely to occur in:
This does not mean that these breeds always develop FIP, it just means that cats of these particular breeds seem to develop FIP more often than other breeds. Male cats may have a slightly increased chance of infection over female cats, but again, this does not mean that only male cats develop FIP. The most consistent factor in FIP infections is age. A large majority of FIP-infected cats are young (under three years of age).
Treatment
Sadly, no FDA-approved, effective treatments exist for FIP. This means that treating FIP is largely based on treating the symptoms and keeping cats comfortable while they fight the virus. Hospitalization with intravenous fluids can help with dehydration. Feeding tube placement for cats not eating may be needed. Antiviral medications to decrease the speed of viral replication can be tried (although most have not been proven to work). Because inflammation is a major issue, anti-inflammatory or immunosuppressant medications such as prednisone may be helpful in some cases.
Cats with wet FIP, even with treatment, often only survive days to weeks. Dry form of FIP is slightly better, but often their survival only lasts for weeks to months. Average survival time from symptoms to passing away is 8-9 days in most cases.
Veterinary Cost
Average cost of veterinary care primarily includes methods of testing and diagnosis. Cost ranges from $150-500. Treatment is generally unsuccessful, so euthanasia may be discussed if quality of life is poor. Euthanasia cost varies greatly depending on region and whether home burial or cremation is requested. Average cost is likely $100-250.
Prevention
Vaccines have been tried but are mostly ineffective. Remember that the issue is mutation of a virus to which the majority of cats are exposed and won't develop symptoms. Potential other methods of prevention include excellent litterbox hygiene (daily cleaning) and avoiding other cats, especially prior to adulthood.
References
Lewis K, O'Brien RT: Abdominal ultrasonographic findings associated with feline infectious peritonitis: a retrospective review of 16 cases. J Am Anim Hosp Assoc 2010 Vol 46 (3) pp. 152-160.
Gibson C, Parry N: Feline Infectious Peritonitis: Typical Findings in a New PCR Test. Vet Med 2007 Vol 102 (6) pp. 375-379.
Richards JR, Elston TH, Ford RB, et al: The 2006 American Association of Feline Practitioner's Feline Vaccine Advisory Panel Report. J Am Anim Hosp Assoc. 2006 Vol 229 (9) pp. 1405-1441.
Wang H, Hirabayashi M, Chambers JK, et al: Immunohistochemical studies on meningoencephalitis in feline infectious peritonitis (FIP). J Vet Med Sci 2018 Vol 80 (12) pp. 1813-1817.
Felten S, Hartmann K, Doerfelt S, et al: Immunocytochemistry of mesenteric lymph node fine-needle aspirates in the diagnosis of feline infectious peritonitis. J Vet Diagn Invest 2019 Vol 31 (2) pp. 210-216.