Feline Infectious Peritonitis

What is FIP?

Feline infectious peritonitis (FIP) is a viral disease of cats caused by certain strains of a virus called the feline coronavirus. 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 major forms of FIP, an effusive, or “wet” form and a noneffusive, or “dry” form. Regardless of which form they ultimately progress to develop, cats infected with FIPV usually first develop nonspecific signs of disease such as loss of appetite, weight loss, depression, and fever. It is also important to note that cases of the effusive form of FIP can evolve into the non-effusive form and vice-versa.

Generally speaking, the signs of the noneffusive form, which may include the non-specific signs listed above as well as neurologic signs including seizures and ataxia (abnormal or uncoordinated movements) develop more slowly than those of the effusive form.

The signs of effusive form of FIP usually develop and progress relatively rapidly and include development of the above-mentioned non-specific signs combined with the accumulation of fluid in body cavities, including the abdomen and the thorax (chest cavity). Affected cats may develop a pot-bellied appearance due to fluid accumulation in the abdomen, and if the fluid accumulation is excessive, it may become difficult for a cat to breathe normally.

Can my cat be tested for FIP?

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. A positive result means only that the cat has had a prior exposure to coronavirus, but not necessarily to FIPV. In spite of this limitation, however, young cats that experience a fever that is not responsive to antibiotics and that have high coronavirus titers are often presumptively diagnosed with FIP (appropriately in most cases). This is particularly true if characteristic fluid (yellow tinged with a high protein and white blood cell concentration) begins to accumulate within body cavities. A healthy cat with a high coronavirus titer (i.e. many antibodies against coronavirus), however, is not necessarily more likely to develop FIP or be a carrier of an FIPV than a cat with a low titer. In cats with suppressed immune systems, FIPV infections may not cause elevated coronavirus titers due to an inability of the immune system to produce sufficient antibodies against the virus.

Other available tests can, in theory, detect the presence of the virus itself. One of these tests, called the immunoperoxidase test, can detect viral proteins in virus-infected white blood cells in tissue, but a biopsy of affected tissue is necessary for evaluation. Another, called the immunofluorescence test, can detect viral proteins in virus-infected white blood cells in tissue or body fluids. More recently, a technology called polymerase chain reaction (PCR) has been used to detect viral genetic material in tissue or body fluid. Although these tests can be useful, none of them is 100% accurate, and each suffers from its own limitations that may lead to false negative or false positive results.

Can FIP be treated?

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.