What Is Feline Infectious Peritonitis(FIP)?
Feline infectious peritonitis (FIP) is the name given to an uncommon, but usually fatal, aberrant immune response to infection with the feline coronavirus (FCoV). Most strains of feline coronavirus are found in the gastrointestinal tract and do not cause significant disease. These are referred to as feline enteric coronavirus (FeCV). Cats infected with FeCV usually do not show any symptoms during the initial viral infection, but may occasionally experience brief bouts of diarrhea and/or mild upper respiratory signs from which they recover spontaneously. FeCV-infected cats usually mount an immune response through which antibodies against the virus are produced within 7-10 days of infection. In approximately 10 percent of cats infected with FeCV, one or more mutations of the virus can alter its biological behavior, resulting in white blood cells becoming infected with virus and spreading it throughout the cat’s body. When this occurs, the virus is referred to as the FIPV. An intense inflammatory reaction to FIPV occurs around vessels in the tissues where these infected cells locate, often in the abdomen, kidney, or brain. It is this interaction between the body’s own immune system and the virus that is responsible for the development of FIP. Once a cat develops clinical FIP, the disease is usually progressive and almost always fatal without therapy that has recently become available, but that has yet to be approved to treat FIP in cats by the Food and Drug Administration (FDA) (see below). To our knowledge, coronaviruses cannot be passed from infected cats to humans.
Is my cat at risk for developing FIP?
Any cat that carries FeCV is potentially at risk for developing FIP, but younger cats are at greater risk of developing FIP, with approximately 70% of cases diagnosed in cats less than 1 1/2 years of age and 50% of cases occurring in cats less than 7 months of age. The most common mode of transmission of FeCV is believed to occur when infected queens pass along the virus to their kittens, usually when the kittens are between five and eight weeks of age. Cats that are housed in high-density facilities (i.e. shelters, catteries) appear to be more susceptible to the development of FIP, as are pure bred cats, male cats, and geriatric cats, for reasons that remain unclear.
What Are the Symptoms of FIP?
Cats that have been initially exposed to FeCV usually show no obvious symptoms. Some cats may show mild upper respiratory symptoms such as sneezing, watery eyes, and nasal discharge, while others may experience mild gastrointestinal signs such as diarrhea. In most cases, these mild signs are self-limiting. Only a small percentage of cats that are exposed to the FeCV develop FIP, and this can occur weeks, months, or even years after initial exposure to FeCV.
There are two main forms of FIP: effusive (wet) and non-effusive (dry). While both types are fatal, the effusive form is more common (60–70% of all cases are wet) and progresses more rapidly than the non-effusive form.
Effusive (wet) FIP
The hallmark clinical sign of effusive FIP is the accumulation of fluid within the abdomen or chest, which can cause breathing difficulties. Other symptoms include lack of appetite, fever, weight loss, jaundice, and diarrhea.
Non-Effusive (dry) FIP
Dry FIP will also present with lack of appetite, fever, jaundice, diarrhea, and weight loss, but there will not be an accumulation of fluid. Typically a cat with dry FIP will show ocular or neurologicial signs including seizures and ataxia (abnormal or uncoordinated movements). For example, the cat may develop difficulty in standing up or walking, becoming functionally paralyzed over time. Loss of vision is another possible outcome of the disease.
How Is FIP Diagnosed?
Diagnosing FIP is challenging. Unfortunately, there is currently no definitive test to diagnose FIP. While antibody levels, or titers, to coronavirus can be measured, they cannot definitively distinguish between exposure to FeCV and FIPV.
Diagnosing effusive FIP
Diagnosis of effusive FIP has become more straightforward in recent years: detection of viral RNA in a sample of the effusion, by reverse-transcriptase polymerase chain reaction (RT-PCR) is diagnostic of effusive FIP. However, that does require that a sample be sent to an external veterinary laboratory. Within the veterinary hospital there are a number of tests which can rule out a diagnosis of effusive FIP within minutes:
- Measure the total protein in the effusion: if it is less than 35g/l, FIP is extremely unlikely.
- Measure the albumin to globulin ratio in the effusion: if it is over 0.8, FIP is ruled out, if it is less than 0.4, FIP is a possible—but not certain—diagnosis.
- Examine the cells in the effusion: if they are predominantly lymphocytes then FIP is excluded as a diagnosis.
Diagnosing non-effusive FIP
Non-effusive FIP is more difficult to diagnose than effusive FIP because the clinical signs tend to be more vague and varied: the list of differential diagnoses is therefore much longer. Non-effusive FIP diagnosis should be considered when the following criteria are met:
- History: the cat is young (under 2 years old) and purebred: over 70% of cases of FIP are in pedigree kittens.
- History: the cat experienced stress such as recent neutering or vaccination.
- History: the cat had an opportunity to become infected with FCoV, such as originating in a breeding or rescue cattery, or the recent introduction of a purebred kitten or cat into the household.
- Clinical signs: the cat has become anorexic or is eating less than usual; has lost weight or failed to gain weight; has pyrexia of unknown origin; intra-ocular signs; icterus.
- Biochemistry: hypergammaglobulinaemia; raised bilirubin without liver enzymes being raised.
- Hematology: lymphopenia; non-regenerative—usually mild—anaemia.
- Serology: the cat has a high antibody titre to FCoV: this parameter should be used with caution, because of the high prevalence of FCoV in breeding and rescue catteries.
Non-effusive FIP can be ruled out as a diagnosis if the cat is seronegative, provided the antibody test has excellent sensitivity. In a study which compared various commercially available in-house FCoV antibody tests, the FCoV Immunocomb (Biogal) was 100% sensitive; the Speed F-Corona rapid immuochromatographic (RIM) test (Virbac) was 92.4% sensitive and the FASTest feline infectious peritonitis (MegaCor Diagnostik) RIM test was 84.6% sensitive.
How Is FIP Treated?
Because FIP is an immune-mediated disease, treatment falls into two categories: direct action against the virus itself and modulation of the immune response.
Until recently, FIP was considered to be a non-treatable disease. While there are still some uncertainties regarding the long-term effectiveness of recently-identified antiviral drugs to treat FIP (most importantly regarding its effectiveness in treating the non-effusive form of FIP), studies in both the laboratory and in client-owned cats with naturally occurring FIP suggest that a drug currently referred to as GS-441524 may ultimately prove to be an effective treatment option for (minimally) the effusive form of FIP. While some cases of the non-effusive form of FIP responded to GS-441524 therapy in these trials, the responses in cases with this form of FIP were not as favorable as those seen in cases of the effusive form. This drug is currently not FDA-approved, however, and while there are a number of sources offering it for sale, anecdotal reports suggest that the products being provided by some of these sources vary widely in both accuracy of reported drug concentration and purity. It is very important to discuss the risks, benefits, and evolving acquisition and regulatory issues with your veterinarian if you are considering therapy with GS-441524. Supportive care, including fluid therapy, drainage of accumulated fluids, and blood transfusions, is also indicated in some cases.
Can I protect my cat from getting FIP?
The only way to definitively prevent FIP in cats is to prevent FeCV infection, which can be challenging given its ubiquitous nature. This is particularly true of cats that are housed in high density (shelters, catteries), and housing cats at a density at or below three per room is recommended to minimize stresses that can be associated with crowded living conditions. It is important to note that while FeCV is quite contagious (it is passed in the feces and saliva of infected cats and infects other cats primarily via the oral cavity), FIPV is not believed to be. Rather, FIP develops in individual cats after they are infected with FeCV and the virus undergoes mutations to become FIPV (FIPV itself is not passed in the feces). Keeping cats as healthy as possible, including preventing infection by other viruses such as feline leukemia virus and calicivirus by appropriate vaccination, where indicated, is likely to decrease the likelihood of FIP. Litter boxes should be kept clean and located away from food and water dishes. Some sources have suggested that newly acquired cats and any cats that are suspected of being infected with FeCV should be separated from other cats, although the usefulness of this management strategy is debatable.
There is only one licensed FIP vaccine available, but this vaccine has questionable effectiveness in preventing FIP, and it is not routinely recommended by the American Association of Feline Practitioners Feline Vaccine Advisory Panel. The vaccine appears to be safe, but the risks and benefits of vaccination should be weighed carefully. Cat owners should consult their veterinarian to help them decide if their cat should be vaccinated.