Any cat that carries FeCV (the ubiquitous, usually benign intestinal form of feline coronavirus from which the FIP form of the virus is derived via mutation) 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, although it can also be passed from one cat to another via feces in more mature cats. 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.

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. Between 5 and 10% 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.

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.

In most cases, a combination of history, physical examination findings, and laboratory test such as those mentioned above are used in concert to arrive at a presumptive diagnosis of FIP.

Until recently, FIP was considered to be a non-treatable and almost routinely fatal disease. While there are still some uncertainties regarding recently-identified antiviral drugs to treat FIP (including their long term effectiveness, ideal minimum dose, potential for the development of drug resistance, and best drug mechanism of action to recommend/pursue), studies in both the laboratory and in client-owned cats with naturally occurring FIP suggest that the drug that has been most extensively studied, referred to as GS-441524, is a safe and effective treatment option for cats diagnosed with of FIP. This drug has been available in Australia and the UK for several years, and has only recently become available as an orally compounded formulation in the US. Prior to this recent US GS-441524 release (and continuing through today), a number of “black market” sources have been offering GS-441524 for sale. Importantly, some reports suggest that the products being provided by some of these sources vary widely in both accuracy of reported drug concentration and purity, making this recent release of a reliably produced oral formulation in the US that much more impactful.  It is very important to discuss the risks and benefits of GS-441524  with your veterinarian if you are considering pursuing therapy with this game-changing drug in a cat suffering from FIP, and a veterinary prescription is required to obtain it. Supportive care, including fluid therapy, drainage of accumulated fluids, and blood transfusions, is also indicated in some cases.

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, pending further research. Rather, FIP is believed to develop in individual cats after they are infected with FeCV and the virus undergoes mutations to become FIPV (FIPV itself is not believed to pass in the feces or other secretions, although ongoing studies may alter this belief). 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.