Multisystem Diseases: feline infectious peritonitis


Feline infectious peritonitis (FIP) is a viral disease of cats that is almost invariably fatal. FIP is caused by a coronavirus, which can invade certain white blood cells called macrophages and other body tissues. This virus is similar to other members of the same virus family that infect pigs, dogs, and humans, but the FIP virus itself can cause disease only in cats. It does so only under certain specific circumstances. Problems with FIP are found primarily in cats who live in or grew up in multicat environments.

Many catteries raising purebreds produce kittens who later develop FIP, and it is a more frequent problem among cats who live in crowded, stressful surroundings where there are concurrent problems with other infections (e.g., respiratory infections, Feline leukemia infection) than in more well-managed environments. Some genetic strains of cats may even be more susceptible than others to disease caused by FIP virus.


FIP infection is transmitted from cat to cat by close contact. Virus is shed (excreted) in oral and respiratory secretions, stool (feces), and urine so it may contaminate food and water bowls, litter pans, clothing, and bedding. Spread via the feces is most common. Virus does not, however, survive longer than a few weeks in the environment and it is easily killed by common household detergents, disinfectants, and bleach. Therefore, problems with FIP infections only persist in households with actively infected cats. In some cases, queens (female cats) transmit the virus to their kittens while they are still in the uterus. This can result in disease that occurs within a few days of birth.


A cat may develop symptoms within a few weeks after or many years after infection with FIP virus. Why there is so much variation in the onset of symptoms is not understood. One theory is that related but harmless coronaviruses that infect the bowel (feline enteric coronaviruses) must mutate to the illness-causing FIP form in an infected cat. It is known, however, that most often affected cats are between six months to two years of age. The most characteristic sign of infection is a persistent fever that does not respond to antibiotic treatment. Some cats lose weight, have poor appetites, and become lethargic and depressed. They may also be anemic. Some cats remain alert and eat well until more specific signs of illness appear and become severe, but all cats sick with FIP have a fever that may fluctuate from just slightly above normal to very high.

Other signs of FIP are classically grouped and used to categorize the illness into “wet” (effusive) or “dry” (noneffusive) forms. In effusive FIP fluid accumulates in the abdomen and/or chest cavities resulting in abdominal distention and/or respiratory distress. In noneffusive FIP signs of almost any organ involvement may be seen. Common symptoms include those caused by kidney failure (increased water drinking and urination), liver disease (jaundice, loss of appetite, vomiting), or pancreatic disease (diarrhea, vomiting, signs of diabetes mellitus). Eye inflammations that may lead to blindness and involvement of the nervous system causing a wide variety of signs ranging from hindleg weakness, loss of balance, to seizures and behavior changes may all be seen. Some cats may have signs found in both wet and dry FIP at once. All these signs are caused by antibody- mediated damage to the small blood vessels (vasculitis) as the body’s own immune system tries to eliminate the virus.


Since signs of FIP can be so wide ranging and thereby mimic other diseases, a veterinarian’s aid is necessary for diagnosis. Analysis of fluids from the chest and/or abdomen, biopsy of affected organs, and blood and other laboratory tests are all used to aid diagnosis. Because FIP antibodies in the blood cross-react with other common but harmless coronaviruses found in healthy cats, and because cats not made ill by FIP virus may still harbor antibodies formed during previous exposure, it is not possible to diagnose FIP on the basis of blood tests alone. Many cats have been euthanized unnecessarily on the basis of inaccurately interpreted blood tests. Lab tests that can detect the damage caused by the virus or the FIP virus itself will make diagnosis easier. Currently veterinarians are able to avoid problems in diagnosis only by thoroughly understanding the disease and by carefully evaluating all available information before making any treatment decisions for their patients.


There is no specific treatment for FIP. Cats who have not become too debilitated or who have signs limited to one organ system (e.g., the eyes) may live comfortably for weeks or months when various kinds of supportive care, such as fluids, vitamins, antibiotics to treat secondary infection, antiviral drugs, and drainage of excessive fluid, are given. A very rare cat may even recover. It is up to you and your veterinarian to decide together what treatment plan is best to follow if your cat is diagnosed as having FIP.

A vaccine against FIP was introduced in 1991. It was designed to help solve the problem of recurrent FIP in multicat environments but has been found to be less effective and more dangerous than originally anticipated.

Cats at low risk of infection should not receive FIP vaccination. Most household pets fall into this category. Ask your veterinarian for information about FIP vaccination if you have a household where FIP is an ongoing problem.