Peritonitis, Infectious (Feline)

by Petside Team

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Feline infectious peritonitis (FIP) is an often-fatal version of a feline enteric coronavirus (FECV). It is found primarily in cats less than 3 years of age. Despite recognizing its existence for decades, the complex pathogenesis of this disease has left many questions unanswered. As a result, testing for FIP is not simple, and treating it is often unrewarding.

Common name: FIP
Scientific name: Feline infectious peritonitis

Diagnosis

Signalment
FIP primarily affects cats under 3 years of age, cats housed in dense populations and cats under stress. A genetic predisposition may also exist. Purebred cats such as Birmans, Abyssinians and Himalayans, among others, may also be at increased risk. Kittens with littermates or mothers definitively diagnosed with FIP are also at higher risk.

Incidence/prevalence
Although the incidence of feline-coronavirus-positive cats is high in most populations, and particularly high-density ones, the incidence of clinical illness associated with the FIP version is low. Serologic studies performed in the United States have shown that between 75 percent and 100 percent of purebred cats in catteries have feline coronavirus antibodies. This compares with 30 percent of non-purebreds living in pet households.

Despite this high number of seropositive cats, only approximately 7 percent to 8 percent of those with antibodies will become ill with FIP. If outbreaks do occur in crowded environments, morbidity and mortality can be high, particularly in younger animals.

Geographic distribution
FIP is found worldwide, especially in dense populations such as in shelters and catteries.

Clinical signs (primary, most to least frequent, scientific term, synonyms)
Often nonspecific, Fever, Anorexia, Lethargy, Wet form (distended, fluid-filled abdomen), Dry form.

Clinical signs (secondary, most to least frequent, scientific term, synonyms)
Jaundice, Unthrifty/poor growth.

Cause (scientific, common term)
Mutation of common feline enteric coronavirus.

Organ systems affected (most to least affected)
Multisystemic (intra-abdominal structures/organs), Urinary , Ophthalmic, Nervous.

Diagnostic tests
Histopathologic evaluation of tissue samples from affected organs after death, Immunofluorescence assay on tissue samples from affected organs after death, Serologic tests/genetic tests (but no definitive test is currently available).

Differential Diagnosis
Feline leukemia virus, Lymphoma, Tumors of the central nervous system.

Overview

Feline infectious peritonitis originates from the family of coronaviruses. The feline coronavirus includes Type 1 and Type 2. There are two subtypes, the nonvirulent and the virulent forms of each type. The nonvirulent form leads to mild or subclinical illness with full recovery. The virulent form is actually a mutation of the virus and leads to clinical FIP. The disease does not have a direct mode of transmission.

For a cat to develop FIP, several factors must come into play. Stress plays a major role in development of the disease. Also, there may be an inherited component to susceptibility as well as other immunosuppressive factors (underlying illness, anesthetic procedure, etc.). The disease is almost always fatal, particularly in cats under 6 months of age.

There are two forms of FIP ‚Äì wet (effusive, fluid) form and dry form. The wet form leads to development of a characteristic fluid in the thoracic or abdominal cavities and is considered a more widespread type within the body. This is most often seen in cats under 1 year of age. The dry form is more difficult to diagnose, as the signs are often non-specific (fever, weight loss, anorexia) and the organ systems affected are difficult to sample (nervous, ophthalmic). The dry form tends to be isolated to specific organ systems. This version is more common in cats over 1 year of age.

Testing for the FIP form of coronavirus is difficult. This virus does not grow well in the lab. There are antigen tests that are relatively specific with effusions or tissue samples, but these samples can be difficult to obtain. There are other tests and assays available, yet none of these are proven to specifically detect FIP. Signalment, history and clinical presentation are all integral parts of the diagnostic process for this disease.

Treatment

There is no cure for feline infectious peritonitis. Mortality is high, close to 100 percent in some situations. Supportive care (hydration, nutrition, ensuring comfort) is vital in helping the patient overcome the virus. It is not impossible for a pet to survive FIP, but it is unlikely.

Home Care
There is no appropriate initial home care for cats diagnosed with Feline Infectious Peritonitis. Care must be initiated at a veterinary hospital.

Professional Care
Veterinary care is instrumental in the diagnostic workup of an FIP-afflicted cat. Baseline blood work and urinalysis are an important first step. Often, advanced imaging such as ultrasound is helpful in obtaining diagnostic information to help determine if a pet truly has FIP. Your vet may also elect to perform certain assays that can help support or deny these suspicions. Again, there is no single diagnostic test for this illness.

Action
Because FIP patients are often febrile, they become dehydrated and refuse food. Intravenous fluids, appetite stimulants and even feeding tubes can be used. Antibiotics may be given to prevent secondary infection during the course of illness. Antiviral agents such as interferon have been used, with low rates of success.

Outcome
Fortunately, relatively few cats in standard environments are at risk of developing FIP. A diagnosis of FIP carries a poor prognosis.

References/Additional Readings

Scott, F.W. Feline Infectious Peritonitis. In: Tilley, L.P., Smith, F.W.K. The 5-Minute Veterinary Consult, 2nd Ed. Baltimore. Lippincott, Williams & Wilkins, 2000; 696-697.

Kennedy, M. Clinical Rounds: Feline Infectious Peritonitis. Davis: American Association of Feline Practitioners/Veterinary Information Network. August 12, 2007.

Scherk, M. Clinical Rounds: Puzzled About FIP? Davis: Veterinary Information Network. November 23, 2003.

Author

Patricia A. Wagner, DVM, MS

Editor

Steven Hansen, DVM, MS, MBA

DABVT, DABT