If you're the owner of a cat, then you should be aware of FIP – Feline Infectious Peritonitis. FIP in cats is a severe and often deadly disease with multiple clinical symptoms. In this blog post, we'll tell you everything you need to know about FIP in cats, including what causes FIP, the signs, and how to treat it. So please keep reading for more information!

What is FIP in cats and what causes it?

FIP stands for Feline Infectious Peritonitis. FIP in cats is a fatal disease that affects multiple systems in the body and is caused by infection with a virulent form of the feline coronavirus called feline infectious peritonitis virus. The virus is highly contagious and can be found worldwide, although it most often affects young cats. The majority of cats (80-90%) test positive for coronavirus, but only a small percentage (5-10%) of them will ever develop FIP.

Feline coronavirus infection is very common and highly contagious. Many cats, almost 80-90% in a multi-cat household are infected. Feline coronavirus infects the intestinal lining and is excreted in feces. Infected cats usually don't have any symptoms or only develop mild, short-term diarrhea. Intestinal infections can cause a temporary viral infection of the blood and seroconversion (the development of antibodies).

FIP in cats

Cats infected with feline coronavirus may develop mutations that cause the feline coronavirus to become the feline infectious peritonitis virus virulent biotype, resulting in FIP. The feline infectious peritonitis virus replicates in white blood cells, which facilitates its ability to disseminate. The exact mutation that leads to the feline infectious peritonitis virus is unknown but may involve genetic mutations.

How is FIP transmitted in cats?

Cats usually get feline coronavirus by the fecal-oral route. This often happens when cats share litter pans with other infected cats. About 35% of cats with feline coronavirus infection excrete the virus in their feces. Some only do this for a few months, but approximately 15% of infected cats are carriers for life and constantly excrete the virus.

FIP in cats develops after feline coronavirus mutates, and rarely comes from direct infection with feline infectious peritonitis virus. There is very little shedding of feline infectious peritonitis virus in feces.

What are the clinical forms of FIP in cats?

Feline infectious peritonitis virus can cause two different clinical forms of FIP in cats: effusive and non-effusive.

Effusive FIP or the wet form of FIP is the more commonly seen form and accounts for approximately 80% of all FIP cases. Effusive FIP is characterized by the accumulation of fluid in the chest (pleural effusion) or abdomen (ascites). These fluids contain inflammatory cells and proteins. Effusive FIP often leads to death within a few days to weeks.

Non-effusive FIP, also called dry FIP, is less common and only accounts for approximately 20% of all FIP cases. Non-effusive FIP is characterized by the buildup of inflammatory cells in different organs, such as the liver, kidneys, and central nervous system. Non-effusive FIP often leads to death within a few months.

Which cats are at risk for FIP?

FIP is most commonly seen in young cats, less than 3 years of age. However, FIP can occur in any age, breed, or gender of cat. Feline coronavirus infection is widespread, and FIP can occur in any cat that becomes infected with the virus. There are breed predilections, however, where Bengals, Rex, Himalayan, and Ragdoll cats are at a higher risk. Male cats are more frequently affected compared to female cats.

What are the symptoms and clinical signs of FIP in cats?

The symptoms of FIP in cats depend on the form of FIP and which organs are affected.

Effusive FIP is characterized by the accumulation of fluid in the chest (pleural effusion) or abdomen (ascites). These fluids contain inflammatory cells and proteins. Clinical signs of the effusion form of FIP in cats may include:

  • Weight loss
  • Anorexia (loss of appetite)
  • Lethargy
  • Jaundice
  • Distended abdomen
  • Difficulty breathing, shortness of breath, or open-mouth breathing

Non-effusive FIP is characterized by the buildup of inflammatory cells in different organs, such as the liver, kidneys, and central nervous system. Clinical signs of the non-effusive form of FIP in cats may include:

  • Weight loss
  • Lethargy
  • Seizures
  • Blindness, or other ocular symptoms
  • Jaundice
  • Anorexia (loss of appetite)

How is FIP diagnosed in cats?

There is not one test that can alone give an accurate diagnosis of FIP in cats. The best way to diagnose it is by using a combination of different methods, as well as taking the cat's history and physical examination into account. Tests that are available that can aid in the diagnosis of FIP in cats include:

  • Bloodwork including a complete blood count (CBC) and biochemical profile: Hyperproteinemia, or an abnormal increase in proteins in the blood, is one of the most consistent abnormalities found in FIP infections in cats. This is due to the increase in gammaglobulins as a result of FIP infection.
  • Fluid analysis: It's helpful to know that analyzing effusions has a higher diagnostic value than blood tests in cases of wet FIP. The fluid is usually straw-colored, viscous, and high in protein content.
  • Viral testing: Viral testing is often unrewarding as there is not currently a way to test for the specific genetic sequence of the FIP virus, so PCR tests cannot tell the difference between mutated and non-mutated coronavirus.

What are the treatment options for FIP in cats?

There is currently no known cure or specific therapy for FIP. Although some experimental therapies show promise, there is a lack of large-scale clinical studies.

Some therapies that are currently being investigated include:

  • Antiprotease Inhibitors
  • Nucleoside Analogs: GS-441524 and GC376 are nucleoside analogs currently being studied as antiviral agents in cats with FIP. Using nucleoside analogs is currently the best chance at curing FIP in cats, although the use is considered off-label and very difficult to source in North America.
  • Recombinant Feline Interferon

Some cats with FIP may benefit from therapy with immunosuppressants since FIP has an immune-mediated component. Common immunosuppressants include prednisolone and cyclophosphamide. Although propentofylline was once thought to be a possible treatment for FIP, a study of cats affected by the disease found that it did not affect either survival time or quality of life.

What is the prognosis for cats with FIP?

The prognosis for cats with FIP is generally poor. The disease is fatal in the vast majority of cases, and most cats do not live longer than 6 months after diagnosis. There are some reports of cats surviving for up to 2 years with FIP, but these cases are very rare.

Frequently asked questions about FIP in cats

Is FIP in cats contagious to other cats

No, the mutated FIP virus is not contagious to other cats. The original, unmutated coronavirus however is very contagious. It is most commonly spread through close contact between infected and uninfected cats, such as sharing food, water bowls, or litter boxes. The virus can also be spread indirectly, for example, if an infected cat sheds the virus in its saliva onto a toy or bedding that is then used by another cat.

How can I prevent my cat from getting FIP?

A modified live virus intranasal vaccine is available to use against feline coronavirus. Studies have revealed however that the efficacy of this vaccine is low and therefore, most veterinarians do recommend vaccination.

You should avoid or minimize stress for your cat by maintaining good husbandry, enriching their environment, and keeping them healthy. You can reduce fecal contamination of the environment by providing adequate numbers of litter trays and cleaning them daily. This will help minimize exposure and spread. When disinfection is required, coronaviruses are susceptible to disinfectants like diluted bleach.

What ocular symptoms of FIP exist?

Ocular FIP is relatively rare, occurring in only about 10% of FIP cases. The most common symptom is a sudden onset of unilateral or bilateral uveitis (inflammation of the eye). Other ocular symptoms include increased tearing, squinting, redness, and apparent cloudiness of the eye. FIP can also cause retinal detachment and hemorrhage, which can lead to blindness.

Can FIP in cats be cured?

There are so-called "black market" therapies available that show excellent promise in achieving a cure for cats with FIP. These are experimental therapies that are not yet approved for use in North America, and as such, are very difficult to source. The most promising of these therapies is the use of nucleoside analogs, which are thought to block the replication of the FIP virus. Before purchasing these products, make sure your veterinarian is comfortable in assisting you throughout the process as there can be side effects and frequent blood tests are often required.

FIP in cats is a serious and often fatal disease caused by the Feline Infectious Peritonitis virus. Symptoms of FIP can vary depending on the form of the disease but may include weight loss, lethargy, anorexia, jaundice, and difficulty breathing. There is no known cure for FIP, but there are some experimental therapies that show promise. Treatment options include antiprotease inhibitors, nucleoside analogs and immunosuppressants. The prognosis for cats with FIP is unfortunately generally poor. We hope this information helps and if you have any questions or concerns, please contact your veterinarian.