Feline Infectious Peritonitis is a devastating viral disease of cats that occurs worldwide and can affect many systems of the body. It is a progressive disease and almost always fatal. FIP affects domestic cats, especially purebred kittens: 70% of FIP cases are in pedigree kittens and cats. It is also a plague in rescue shelters and can be a danger to big cats kept in zoo environments. FIP occurs when the cat mounts an overly inflammatory immune response to feline coronavirus infection.


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FIP is a complex disease, and we have an in-depth look here, but if you want a quick and concise primer, our FIP at-a-glance provides you with the basics of the disease.

What is Feline Infectious Peritonitis?

Feline Infectious Peritonitis (FIP) is the result of an excessive inflammatory response to infection with feline coronavirus (FCoV).
FCoV infection is ubiquitous and extremely common in multi-cat environments.
Only a small percentage (up to 12%) of infected cats develops FIP.
Stress (adoption, neutering, boarding, etc.) is a contributing factor to the development of FIP.
 Although cats of any age can develop FIP,  it mainly occurs in cats < 2 years old, and pedigree cats seem to be more affected.
FCoV can survive for up to 7 weeks in the environment.
FCoV is a fragile virus easy to inactivate by using cat-friendly detergents and disinfectants (1:32 solution of household bleach in hot water is ideal).

How do cats become infected with FCoV?

Feces of shedding cats are the primary source of FCoV infection.
FCoV can be transmitted indirectly (litter trays, shoes, brushes, vacuum cleaners, etc.).
Cats start shedding FCoV within one week after infection and continue for weeks or months and a small percentage of cats, for life.
Most FCoV infected cats stay healthy, showing no signs whatsoever while some may show mild enteritis.
The viral load and the cat’s immune response determine whether FIP will develop.
FIP is NOT contagious – FCoV IS!
Whenever FCoV is present in a cat, there is the potential for FIP to develop. On the other hand, no cat can develop FIP if not infected with FCoV. NO FCoV = NO FIP!

Clinical signs of FIP

Persistent and antibiotic-resistant fever, lethargy, anorexia, weight loss and overall malaise are common initial clinical signs of FIP.
If the disease develops – two forms of FIP are described, although one can morph into the other:
An effusive (wet) form, characterized by abdominal and/or thoracic effusions and vasculitis
A non-effusive (dry) form, characterized by granulomatous lesions in various organs
Although FIP is separated into two forms (wet and dry) there is really a gradient between these forms, and sometimes signs of both forms can be seen.
 The clinical presentation of FIP is highly variable, depending on the distribution of the vasculitis and the location of the pyogranulomatous lesions.
Neurological signs (seen in about 10% of cases) include ataxia (impaired balance or coordination), hyperesthesia (abnormal increase in sensitivity to stimulus), nystagmus (involuntary eye movements), seizures, paralysis, and behavioral changes.
Ocular involvement with uveitis is common in dry FIP cases, other signs include:
Changes in iris color
Dyscoria (any abnormality in the shape of the pupil of the eye)
Anisocoria (unequal size of the eye’s pupils) 
Iritis (inflammation of the iris of the eye)
Sudden loss of vision 
Hyphema (collection of blood in the front of the eye)

Cutaneous signs while not common, have been reported including nodular lesions, skin fragility, and vein inflammation.

How is FIP diagnosed?

The cat’s background, recent history, clinical signs, laboratory changes, FCoV antibody titers and FCoV RT-PCR testing should all be used as part of diagnostic procedures.
High FCoV antibody titers alone have NO diagnostic values. To be clear: A positive FCoV test result DOES NOT mean the cat has FIP!
There is no non-invasive confirmatory test available for dry FIP, but a fine needle aspirate is less invasive than a full biopsy and a positive FCoV RT-PCR test on a mesenteric lymph node biopsy is highly indicative of FIP.
Effusions suggestive of FIP first can be tested via Rivalta Test (easy and inexpensive) and then submit to a reliable laboratory for FCoV RT-PCR.
Blood samples should NOT be sent to a specialized laboratory for RT-PCR as negative results are NOT uncommon in cats with FIP and positive results can occur in cats without FIP.
Laboratory findings suggestive of FIP include:
Lymphopenia (low level of lymphocytes in the blood)
Non-regenerative anemia
Increased total serum protein
Hyperglobulinemia (a large amount of gamma globulins in the blood)
A low albumin/globulin ratio ( <0.8 FIP is extremely likely)
High alpha-1 acid glycoprotein (but AGP rises in any acute infection)
High FCoV antibody titers

When possible, fine needle aspirates from pyogranulomas or effusions should be sent to a specialist veterinary laboratory for FCoV RT-PCR, immunofluorescence, immunohistochemistry testing (biopsy) and results are almost 100% predictive of FIP.

What can you expect?

The prognosis for cats with FIP is extremely poor. Average survival time after diagnoses is 3 weeks in effusive FIP, longer in non-effusive FIP. However, there are several documented cases worldwide of cats surviving months, even years after diagnosis (generally cases of dry FIP – properly diagnosed and treated early on.)
Treatments are rarely curative. Long-term survival is possible in some cases, but in spite of recent claims, no treatment that eliminates the virus .
Supportive treatments are aimed at suppressing the inflammatory and detrimental immune response.
Euthanasia should be considered ONLY after every effort has been made to obtain a definitive diagnosis. 
In a single-cat household where a cat has died of FIP – it is recommended to wait at least seven weeks before bringing a new cat.
In multi-cat households, after a FIP death, the remaining cats are likely to be FCoV infected. Testing current and new cats (FCoV antibodies and FCoV RT-PCR on feces) before the introduction of a new cat or kitten is highly recommended.
Reduction of FCoV contamination can be achieved by strict hygienic protocol and by keeping cats in small groups with sufficient and frequently cleaned litter trays (1 per cat + 1) or outdoor access (if safe).

Watch Dr. Addie’s instructional videos to understand how cats become infected with FCoV, and how FCoV becomes FIP.

How cats become infected with FCoV.
Dr. Diane D. Addie

Pathogenesis of Feline Infectious Peritonitis (FIP) – the infection of the monocyte.
Dr. Diane D. Addie

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Are you looking for in-depth information about Feline Infectious Peritionitis? Our  FIP in-depth section is what you need. Please go to this page to get started.

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