What Is Feline Infectious Peritonitis (FIP)?
Feline Infectious Peritonitis (FIP) is a fatal disease caused by mutation of the Feline Coronavirus (FCoV). According to a review in the Journal of Feline Medicine and Surgery (Pedersen, 2009), approximately 25–40% of domestic cats carry feline coronavirus, with infection rates in multi-cat environments reaching as high as 80–90%.
However, carrying feline coronavirus does not mean a cat will develop FIP. FIP only develops when the virus mutates within an individual cat and the cat's immune system is unable to effectively control the mutated virus. According to current research, approximately 5–12% of FCoV-infected cats ultimately develop FIP.
Two Forms of FIP
| Form | Alternative Name | Key Features |
|---|---|---|
| Wet (Effusive) | Effusive form | Fluid accumulation in the abdominal or thoracic cavity; abdominal distension or difficulty breathing. Faster progression |
| Dry (Non-effusive) | Granulomatous form | Granulomatous lesions in the eyes, brain, liver, kidneys, and other organs. Slower progression but more difficult to diagnose |
Some cases may exhibit features of both forms simultaneously (mixed form).
Common Symptoms
- Persistent Fever: Recurring fever unresponsive to antibiotic treatment
- Decreased Appetite and Weight Loss
- Lethargy: Gradually becoming sleepy and less active
- Abdominal Distension (wet form): Ascites causing the abdomen to enlarge
- Difficulty Breathing (wet form): Pleural effusion compressing the lungs
- Jaundice: Yellowing of the gums and inner ear flaps when the liver is affected
- Eye Abnormalities (dry form): Iris color changes, unequal pupil sizes, anterior chamber opacity
- Neurological Signs (dry form): Unsteady gait, head tilt, seizures
How Is It Diagnosed?
Definitive diagnosis of FIP in a living animal is very challenging. According to diagnostic guidelines in the Journal of Feline Medicine and Surgery(Tasker, 2018):
- Blood Tests: Hyperglobulinemia, low albumin-to-globulin ratio (A:G < 0.4 is highly suspicious), anemia
- Ascitic/Pleural Fluid Analysis (wet form): High-protein, low-cellularity exudate; positive Rivalta test
- FCoV Antibody Titer: A high titer is suggestive but cannot confirm diagnosis (it only indicates prior exposure to coronavirus and is non-specific)
- Immunohistochemistry: Detection of FCoV antigen in tissue or body fluid samples— the closest method to a definitive diagnosis
Important Reminder: A positive "coronavirus antibody" result alone cannot diagnose FIP. A positive coronavirus antibody simply means the cat has been exposed to feline coronavirus (which is very common) and does not indicate FIP. Definitive diagnosis requires a combination of clinical signs, blood tests, and fluid analysis.
Treatment Breakthrough: GS-441524
FIP was previously considered an almost universally fatal disease. However, a major treatment breakthrough has emerged in recent years. According to a study published in theJournal of Feline Medicine and Surgery (Pedersen et al., 2019), the antiviral drug GS-441524 demonstrated remarkable efficacy in clinical trials:
- Out of 31 cats with confirmed FIP, after 12 weeks of treatment,25 (81%) achieved long-term remission
- Wet form FIP typically responds faster and more dramatically to treatment than the dry form
- The earlier treatment begins, the higher the success rate
In 2024, the U.S. FDA conditionally approved the first feline GS-441524 product (a prodrug of Remdesivir). Treatment is now available at many veterinary hospitals, though costs are significant and the treatment course is lengthy (typically 84 days).
Preventive Measures
- Reduce Infection Risk in Multi-cat Environments: Maintain good hygiene; keep litter boxes away from food bowls (fecal-oral transmission)
- Reduce Stress: Stress can impair the immune system's ability to control the virus
- Quarantine New Cats: Newly introduced cats should be isolated and observed first
- Keep the Environment Clean: FCoV can survive in the environment for several weeks but is susceptible to common disinfectants (such as diluted bleach)
References
- Pedersen, N.C. (2009). A review of feline infectious peritonitis virus infection: 1963-2008. Journal of Feline Medicine and Surgery, 11(4), 225-258.
- Pedersen, N.C. et al. (2019). Efficacy and safety of the nucleoside analog GS-441524 for treatment of cats with naturally occurring feline infectious peritonitis. Journal of Feline Medicine and Surgery, 21(4), 271-281.
- Tasker, S. (2018). Diagnosis of feline infectious peritonitis: Update on evidence supporting available tests. Journal of Feline Medicine and Surgery, 20(3), 228-243.
- Addie, D.D. et al. (2009). Feline infectious peritonitis. ABCD guidelines on prevention and management. Journal of Feline Medicine and Surgery, 11(7), 594-604.