Feline Infectious Peritonitis

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What is it?

Feline infectious peritonitis (FIP) is an infectious disease caused by a mutation in the feline enteric coronavirus (FCoV) which changes it from a relatively harmless virus into a deadly one. This deadly virus then attacks the immune-system causing a fatal chain of events.

Why is it important?

Many cats are infected with FCoV and have no symptoms (except occasionally short-term diarrhoea which goes away) but despite this few develop FIP. Cats get FIP in one of two ways: the virus in their body changes to become the deadly version, or they are infected by other cats shedding the deadly version of the virus in their faeces (but this is thought to be quite rare).

What’s the risk?

Although any cat can develop FIP it is more common in cats under 2 years old or over 10 years old. It is also seen more often in pedigree breeds or multi-cat households. Stress (e.g. moving house, introducing new pets) is often associated with cats developing the infection as it lowers the immune system so the body doesn’t destroy the virus.

What happens to the cat?

There are two forms of FIP described, wet and dry, although it is common to get a combination of the two. Symptoms alone are not specific to the disease but can include:

  • General symptoms: fever, decreased appetite, lethargy, weight loss
  • Wet FIP: Fluid build up in the abdomen or chest making them look pot-bellied or have difficulty breathing. Fluid can also leak into the sack surrounding the heart making it more difficult to pump blood around the body.
  • Dry FIP: granulomatous lesions (lumps of inflammation) can form anywhere in the body but occur in the nervous system and the eye most often. This can result in neurological symptoms such as difficulty walking, blindness and bleeding within the eye.

  • How do you know what’s going on?

    Diagnosing FIP can be complicated but the age and symptoms of the cat may make your vet more suspicious. Different tests are used depending on the type of FIP suspected.

    Routine blood tests often show non-specific changes such as increased levels of immune proteins, changes in white blood cell numbers and anaemia. Blood tests to assess antibody levels to FCoV have limited use in most cases, as they just indicate virus exposure (which is common) and not a mutation. However, a negative cat is unlikely to have FIP.

    X-rays and Ultrasound scans can be used to check for the fluid found in wet FIP, which can then be sampled with a needle and syringe to use for testing. The fluid is usually yellow and thick but this is not specific to FIP. A negative “Rivalta test” on the fluid can rule out FIP. While a positive test does not guarantee a cat has FIP, it does increase the likelihood, especially in young cats. This test can be followed with PCR tests which look for DNA associated with the mutated virus. If this test is positive then FIP is likely, but again, a negative result does not completely rule out FIP because virus DNA is not always detected in the fluid.

    Cats showing neurological symptoms may require a cerebrospinal fluid tap to gather fluid for testing. Other dry forms of FIP may require a biopsy (tissue sampling) for testing.

    Currently, the definitive test to confirm FIP is immunostaining (fluid samples) and immunohistochemistry (tissue samples). Markers attach to the mutated virus within the samples so they can be seen under a microscope, like white items shining under a UV light.

    What can be done?

    Sadly, FIP is a fatal disease and the majority of cats die within a week of diagnosis. Anti-inflammatory and antiviral treatment may sometimes prolong life, especially with the dry form of the disease, sometimes for several months. For many years, euthanasia has been recommended to stop the cat from suffering.

    However, there are now new and experimental treatments available. Although very expensive and not licensed in the UK for use in cats, one of these can now be sourced in the UK by a qualified veterinary surgeon legally, and it appears to be highly effective.

    How can I protect my pet?

    The biggest concern for many cat owners is the risk of other cats in the same household developing FIP. Evidence shows that cats suffering from FIP rarely shed the mutated virus into the environment and so are not likely to pass on the disease. Cats that have been living with an FIP cat are likely to have already been exposed to the same strain of FCoV before it mutated and so should have a degree of immunity.

    New cats that have not been living with the FIP patient, however, will not have immunity and this situation should be avoided. Household cleaners (e.g. bleach) destroy the virus but it can live for 7 weeks in a dry environment. Therefore after the loss of a cat with FIP it is recommended that all bedding/toys etc be destroyed, the environment cleaned and a waiting period of at least 2 months occurs before another cat is introduced.