group of kittens on the grass

Feline Coronavirus (FCoV) and Feline Infectious Peritonitis (FIP)

What is feline infectious peritonitis?


  • Feline infectious peritonitis (FIP) is an infectious disease that can be deadly to cats.
  • Feline Coronoavirus (FCoV) is a common viral infection in cats that most often causes mild gastrointestinal clinical signs.
  • FCoV can undergo mutations and transform into FIP virus, which allow it to spread beyond the gastrointestinal tract.
  • While FCoV is contagious, FIP is rarely transmitted between cats.
  • FIP causes systemic inflammation, resulting in a variety of clinical signs, which can make diagnosis challenging.
  • There is no FDA-approved therapeutic for the treatment of FIP in the United States.

Feline infectious peritonitis, or FIP, is a feline coronavirus variant that can be deadly to cats. It occurs when feline coronavirus (FCoV), commonly found in the feline gastrointestinal tract of cats, undergoes genetic mutations that alter its specificity from affecting intestinal cells to impacting cells of the immune system. The virus then spreads through the cat’s body, causing systemic inflammation.

Feline coronavirus and FIP are found worldwide in domestic and wild cats. Whereas 50-90% of cats test positive for FCoV-specific antibodies, less than 5% of FCoV-infected cats develop FIP. A consistent mutation in FCoV that leads to FIP has not been identified. Rather, FIP develops sporadically within each individual cat that becomes affected. A number of factors likely play roles in the development of FIP, including viral genetics, dosage, and virulence, as well as host immunity, age, breed predisposition, stress, and environmental factors.

Since some cat breeds appear to be more susceptible, a genetic component to susceptibility has been suggested, with inbreeding being a risk factor for disease development. Males also appear to be more prone to FIP than females. FIP is usually diagnosed in cats younger than three years-of-age, although cats of any age can develop the disease.

Feline infectious peritonitis generally presents in two forms, wet (effusive) and dry (non-effusive), based on the immune system response. In the wet form, fluid is produced in the abdomen and/or chest. Wet FIP reportedly accounts for approximately 80% of cases and is more common in young cats. Inflammation in organs affected by the dry form does not produce excess fluids. In some cases, affected cats can show signs of both forms.

The most common route of FCoV infection is fecal-oral transmission. It is a significant problem in households with multiple cats, with shared litter boxes being a primary source of transmission.

What are the clinical signs of feline infectious peritonitis?

Clinical signs of FIP vary depending on which organs are involved. Regardless of which form of FIP is present, the most common clinical signs are lethargy, fever, enlarged lymph nodes, inappetence, weight loss, and a deteriorating hair coat. Cats affected with the wet form of FIP can exhibit a swollen abdomen, or difficulty breathing, depending on whether fluid has accumulated in the abdomen or chest, respectively. Cats with the dry form can show a variety of clinical signs, depending on which organ(s) are involved. Approximately 5-10% of FIP cases with the dry form include neurologic signs such as ataxia, involuntary movement of the eyes (nystagmus), and seizures. Ocular signs such as uveitis can also occur in cats with FIP.

How is feline infectious peritonitis diagnosed?

Diagnosing FIP can be challenging. Patient history, clinical signs, levels of FCoV antibodies, PCR to look for FCoV genetic material, or special stains to look for viral antigen may be used for FIP diagnosis. Diagnostic imaging, including X-rays, ultrasound, or MRI may be performed depending on the site of infection.

Cats affected with FIP often exhibit high protein levels in the blood due to increased globulins, proteins that have important roles in immune function. In particular, the albumin to globulin ratio is used to distinguish FIP from other diseases. If the blood serum albumin to globulin ratio is less than 0.8, there is an increased chance that the cat has FIP; however, this is not seen in all cats with FIP.

Protein and cell counts in abdominal or thoracic fluid may also be used for FIP diagnosis. Fluid with high protein and low cell counts are consistent with wet FIP.

It is important to note that changes to the albumin to globulin ratio, as well as positive Rivalta tests can occur with other diseases as well, so they should be used in context with other information and not as sole indicators of FIP.

How is feline infectious peritonitis treated?

There is no effective long-term management or successful treatment approved for veterinary use in the United States. Previous research conducted at UC Davis indicated promising treatments, including the antiviral drug GS-441524 which is closely related to remdesivir. Remdesivir currently has emergency use authorization from the FDA to treat COVID-19 in people. If it becomes fully licensed, veterinarians could prescribe it to cats affected with FIP.

The antiviral drug GS-441524 is closely related to remdesivir and research has shown that it is safe and effective for treating cats affected with FIP. However, veterinarians in the U.S. currently cannot legally prescribe this drug. This treatment is expensive and requires proper monitoring.  Recent studies indicate that multiple other anitivirals shown to be effective against SARS CoV-2 in human patients effectively block replication of feline infectious peritonitis virus.

Prior to attempting any treatment, owners should consult with a veterinarian that is knowledgeable about FIP. It is important to confirm that the patient suffers from FIP and not another disease. It is also important for a veterinarian to aid in proper monitoring of cats being treated for FIP.

Supportive treatment may include fluids, nutritional support, and medications to suppress immune overreaction.

UC Davis researchers are conducting clinical trials aimed at assessing antiviral drug treatments in cats with FIP. Enrollment is currently open for the following clinical trials. Please visit the study pages for additional information.

What is the prognosis for feline infectious peritonitis?

The prognosis is poor for cats with FIP. Up to 95% of cats diagnosed with FIP die without treatment. Longevity and quality of life may be improved with supportive care.

How can feline infectious peritonitis be prevented?

The best way to prevent FIP is to reduce the number of cats in the environment, especially the number of young cats. In multi-cat environments, keep possibly contaminated surfaces clean.

There are currently no treatments for healthy FCoV-positive cats that have been shown to prevent development of FIP and antiviral therapy is not recommended.

For more information

UC Davis General Feline Infectious Peritonitis Resources

UC Davis Launches Clinical Trials to Treat a Deadly Coronavirus Disease in Cats

Feline Infectious Peritonitis Therapeutics/Clinical Trials Team

UC Davis Veterinary Clinical Trials

UC Davis has long history of studying feline infectious peritonitis

*This article may not be reproduced without the written consent of the UC Davis School of Veterinary Medicine.

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