Feline Infectious Peritonitis (FIP)

Infectious peritonitis in cats

Feline Infectious Peritonitis or FIP is an invariably fatal viral disease that creates a lot of fear and confusion in shelters despite the fact that it is not very common in the general cat population. In fact, one estimate is that it only affects approximately 1% of cats seen by veterinarians for treatment. It is most prevalent amongst cats that are housed together, especially when overcrowding leads to stress. While it would seem that FIP would be disastrous for shelters, fortunately, it is not transmitted the same way many other contagious diseases are and therefore has less of an impact than might be expected. Although there is a vaccine available against the disease, there is still much research being conducted into how the disease is transmitted and how to diagnose and ultimately treat it.

Cause || Transmission || Symptoms || Diagnosis || Treatment || Comments || Disease Control Methods || Vaccination


FIP is caused by a corona virus (FCoV). The disease most frequently affects cats under 2 years of age, but cats of any age are susceptible. There are two FCoV strains seen in cats, one being FECV, which generally causes diarrhea or no symptoms, and the other, FIPV which causes FIP. Together, the two virus strains are known as FCoV. Diagnosis of FIP is easier said than done because differentiation between the two virus strains is extremely difficult, and it is currently believed that FCoV has the potential to develop into FIP from either strain, not just the FIPV strain.

FCoV is a fairly fragile virus. Although it can survive outside the cat's body in a dry environment for up to about 7 weeks (compared to parvo virus, which can survive upwards of a year), it is fairly easy to kill with routine disinfection. Household bleach diluted 1:32 with water is an inexpensive yet effective disinfectant.


FCoV is shed primarily in the feces. In the early stages of the disease, it may also be shed in urine, saliva and. respiratory secretions.

Cats become infected with FCoV primarily by ingesting or inhaling the virus. However, it is possible that it is spread through grooming and direct close contact between cats or through indirect contact with fomites, which are contaminated objects. The most common fomites found in shelters are litter trays, food bowls, hands and clothing.

According to Dr. Susan Little, of the Cat Fancier's Association Health Committee, "Transmission of FIP from cat to cat is considered rare." One theory about FIP is that cats become infected with FCoV, which then mutates in the cat's body into the deadly FIPV form to cause FIP. Pedigree kittens and certain large cats like cheetahs may be genetically predisposed to developing the disease. A cat with FIP will shed FCoV, not FIP. Kittens, older cats, or cats that have other diseases or are suffering from stress develop FIP because their immune systems are unable to fight the virus. Animals who are immune-compromised because of other diseases or infections like FIV or FeLV are most likely to develop FIP. In an ironic twist, it is believed that in some cats the immune system may actually contribute to the development of FIP by forming virus and antibody complexes that are harmful to the body rather than destructive to the virus.

FCoV is extremely contagious. Approximately 95-100% of cats that are exposed to FCoV will become infected with it. However, most will produce antibodies within two to three weeks of exposure (seroconvert) and the vast majority of them do not develop FIP. Although statistics vary, up to 75% of healthy cats that have been exposed to and naturally infected with FCoV will shed the virus either continuously or intermittently for up to one year after infection. Most healthy FCoV shedders stop shedding virus after that. According to Greene's text on Infectious Diseases of the Dog and Cat, "evidence of virus shedding is never a good reason to euthanize a cat because most FCoV shedders stop within a year and less than 10% develop FIP".

The incubation period (time from exposure to the virus until the development of clinical signs) of FIP can be a few days to months.


FCoV affects many different organ systems, creating a whole range of symptoms, or none at all. Early signs of FCoV exposure in some cats can be mild upper respiratory disease, including runny eyes, sneezing, watery nasal discharge or vomiting and diarrhea. This would be a result of FECV infection. FIP typically shows up as one of two forms, the wet (effusive) form and the dry (noneffusive) form.

The dry form usually has a slow onset. Signs include fever, weight loss, depression, loss of appetite, difficulty breathing, vomiting and diarrhea, anemia, eye problems (hemorrhage, eye color change, blindness), kidney and liver disease and neurological signs such as seizures, lameness and staggering gait.

The most characteristic symptom in the wet form is abdominal swelling due to fluid accumulation. Other signs include fever, weight loss, jaundice, rapid or difficult breathing, enlarged scrotum, pale mucus membranes, and muffled heart sounds. The appetite may or may not be normal, and the cat may or may not be depressed.

Regardless of the form it takes, once clinical signs of FIP appear, death is inevitable.


FIP is very difficult to diagnose. There is no definitive blood test currently available that is specific enough to differentiate FECV from FIPV. In other words, although serology tests are commonly used to check for the presence of antibodies to the virus, a positive antibody titer is not diagnostic for FIP. A positive test simply means the animal has been exposed to FCoV and has produced antibodies against it. Healthy cats may be seropositive (meaning they have antibodies against FCoV), while cats with the wet form of FIP may be seronegative because the virus in their body binds with the antibodies, rendering the test inaccurate. To further complicate matters, test results must be interpreted cautiously because laboratories are notorious for producing inconsistent results when testing for this particular disease.

It was believed that a specialized test called the polymerase chain reaction (PCR) assay that checks for the virus rather than antibodies would be more specific for diagnosing FIP, but it is expensive, not widely available and it is still being debated as to whether it is specific and definitive for FIP. The most accurate method of diagnosing the disease is through tissue testing. There is an immunoperoxidase test that detects virus-infected cells in the tissues. It, like routine tissue testing, requires a biopsy to perform this test.

A diagnosis of FIP is made by carefully correlating all the test results with the history and clinical symptoms. Even then, the diagnoses are often considered to be presumptive. The most accurate, definitive diagnoses are made at necropsy (autopsy).


There is no treatment or cure for cats that are sick with the disease. The mortality rate is nearly 100%. Palliative measures exist that may make the cat more comfortable, but once clinical signs appear, most animals only live for a few weeks up to a year. Furthermore, there are no treatment or preventive measures to prevent cats that are infected with FCoV from developing FIP. Treatment of animals in the shelter is not advised.


Many of the measures that would be recommended to prevent FIP in catteries are inappropriate in shelters because of the open nature of admissions in shelters and the limited usefulness of testing. The temptation is to test all cats in the shelter for FCoV whenever a case of FIP is diagnosed, but the testing has little value for determining if cats are suitable for rehoming. Serology tests are not specific for FIP, and once FCoV is in the shelter, most cats will have been exposed, developed an antibody titer against it and thus test positive. The test has no predictive value for determining which healthy cats will develop the disease. It can be said that a cat that tests negative for FCoV cannot develop FIP, but that cat may actually be at greater risk than a healthy positive cat because he has no previous exposure and thus no immunity to it.

It must be remembered that a healthy cat that tests positive for FCoV has a less than 10% chance of developing FIP. Widespread or routine testing for FCoV in shelters is not recommended, and no healthy shelter cat should be euthanized for FIP because of a positive serology test. Cats in shelters that are seropositive can and should be rehomed.


In case of an outbreak of the disease, some of the following measures should be followed:

  1. Establish a good preventative health care program to minimize the presence of concurrent diseases that will render animals more susceptible to developing FIP.
  2. Isolate sick animals immediately.
  3. Pay meticulous attention to daily cleaning and disinfecting of the kennels and wards.
  4. Take special care of litter boxes. Use disposable trays or disinfect with bleach diluted 1:32 with water. Dispose of feces carefully, as they will be one of the main sources of the virus.
  5. Minimize fomite transmission of the disease by training all staff, volunteers and the public the importance of good sanitation and washing one's hands.
  6. Separate food as far away as possible from the litter box.
  7. Avoid overcrowding, as this leads to stress. Cats should be housed singly if possible.
  8. If testing is conducted and cats are housed together, they should be separated into seropositive and seronegative groups.
  9. Minimize stress.
    1. Establish and maintain routines for feeding and cleaning.
    2. Reduce noise levels.
    3. Maintain proper environmental conditions and ventilation.
    4. Provide toys and other items for behavioral enrichment.
  10. Segregate animals by age and litter.
  11. Feed properly, utilizing the most nutritious food available.
  12. Test for FeLV and FIV and isolate animals with positive test results.
  13. Separate seropositive queens from their kittens at 5-6 weeks of age to prevent the transmission of the virus to the kittens once their maternal antibodies have waned. This method has recently been challenged as a successful management technique, but is worth a try as one of several methods of controlling the problem.
  14. Although generalized testing is not recommended, if the shelter decides to test cats for FCoV:
    1. Try to adopt seropositive cats to adopters who have other seropositive cats or to single cat households.
    2. Try to avoid placing seronegative cats in seropositive households.
    3. Advise retesting of seropositive cats 6-12 months later to see if they have become seronegative.


There is an intranasal vaccine for FIP that has been available since 1991. Animals must be at least 16 weeks of age to be vaccinated, and two doses given 3 weeks apart are required. Cats will shed vaccine virus for 4 days from the nose and mouth after vaccination. While the vaccine is considered by most to be safe, its efficacy is in question. It has not been recommended for routine use in shelters. Vaccination will cause seroconversion and low antibody titers that will interfere with future FCoV testing. It is also not effective in animals that are incubating the disease, so FCoV antibody testing before vaccination would yield the most effective results.

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