🚨 THIS IS A MEDICAL EMERGENCY
Seek immediate veterinary attention. Do not wait or attempt home treatment. Every minute counts.
Feline Infectious Peritonitis (FIP)
Feline coronavirus mutation (FCoV → FIPV)
A once-fatal viral disease caused by a mutated feline coronavirus. Historically a death sentence, but now treatable with antiviral therapy (GS-441524/Remdesivir). Early detection is critical.
Last updated: 2026-05-10
Severity
severe
When to Act
🚨 Immediate Emergency Care
Symptoms & Signs
Persistent fever unresponsive to antibiotics
Waxing and waning fever that doesn't respond to standard treatments.
Weight loss and muscle wasting
Progressive loss of body condition, especially over the spine.
Lethargy and decreased appetite
Cats become increasingly withdrawn and stop eating.
Abdominal distension (wet form)
Fluid accumulation in the abdomen giving a pot-bellied appearance.
Difficulty breathing (wet form)
Fluid in the chest cavity compresses the lungs.
Neurological signs (dry form)
Seizures, ataxia, nystagmus, hind limb weakness — indicates brain/spinal cord involvement.
Ocular changes (dry form)
Uveitis (eye inflammation), color change, or cloudy appearance of the eyes.
Behavioral Changes to Watch For
Pets can't tell us what's wrong. These behavioral changes are often the first clues that something is wrong.
🐾 Profound lethargy and withdrawal
Cat loses interest in everything — food, play, interaction.
What You May Notice:
Your cat stops greeting you, hides constantly, and seems completely disconnected.
🐾 Kittens stop growing
In young cats, FIP causes a failure to thrive and cessation of growth.
What You May Notice:
Your kitten that was gaining weight well suddenly plateaus or loses weight.
Causes & Risk Factors
Causes
- •Mutation of common, usually harmless feline enteric coronavirus (FECV) to virulent FIPV
- •The mutation is spontaneous and unpredictable — it's not passed from cat to cat
- •Immune system's response to the virus causes the damage, not the virus itself
Risk Factors
- ⚠Young cats (highest incidence under 2 years, especially 3-16 months)
- ⚠Multi-cat households, shelters, catteries (higher coronavirus prevalence)
- ⚠Stress (adoption, surgery, vaccination, rehoming)
- ⚠Genetics — certain breeds and lines have higher susceptibility
- ⚠Immunocompromised cats (FeLV, FIV)
How It's Diagnosed
- 1Clinical signs and signalment (young cat, multi-cat origin, persistent fever)
- 2Blood work: elevated total protein, low albumin:globulin ratio (<0.4 strongly suggestive)
- 3Effusion analysis (wet form): straw-colored, sticky fluid with high protein
- 4Rivalta test on effusion fluid (high negative predictive value)
- 5PCR on effusion or tissue — NOT definitive alone; must correlate with clinical picture
- 6No single definitive antemortem test exists — diagnosis is based on cumulative evidence
Treatment Options
Antiviral Therapy (GS-441524 / Remdesivir)
Transformative treatment that has changed FIP from fatal to treatable.
Steps
- 1.GS-441524 (or Remdesivir) daily subcutaneous injections for 84 days
- 2.Dose based on form: wet FIP (lower), dry/ocular (medium), neurological (highest)
- 3.Supportive care: nutritional support, fluid therapy as needed
- 4.Monitor weight, temperature, and clinical signs throughout
- 5.84-day observation period after completing treatment
Expected Outcome
80-90%+ cure rate when treatment is started before end-stage disease.
Precautions
- !Treatment requires significant commitment: daily injections for 12 weeks
- !GS-441524 must be sourced through compounding pharmacies or specialized providers
- !Injectable form is painful (Remdesivir) to well-tolerated (GS-441524)
- !Oral GS-441524 now available in some regions for maintenance phase
Supportive Care
Essential while antiviral therapy takes effect.
Steps
- 1.Nutritional support — appetite stimulants (mirtazapine), feeding tube if needed
- 2.Drainage of effusion if causing respiratory distress
- 3.Pain management
- 4.Treatment of secondary infections
Expected Outcome
Maintains quality of life during the initial treatment phase.
Precautions
- !Effusion drainage provides only temporary relief and depletes protein
Common Medications Used
| Medication | Usage | Important Notes |
|---|---|---|
| GS-441524 | Direct-acting antiviral — the active metabolite of Remdesivir | Not FDA-approved for veterinary use but widely available through compounding. Has revolutionized FIP treatment. |
| Mirtazapine | Appetite stimulant | Applied as transdermal gel. Essential for maintaining nutrition during treatment. |
Prevention
- ✓Reduce coronavirus exposure: frequent litter box cleaning, minimize cat density
- ✓Reduce stress in multi-cat environments
- ✓Early weaning and isolation of kittens from coronavirus-positive queens (controversial and difficult)
- ✓No commercial vaccine available in North America
When to See a Veterinarian
- 🚨Persistent fever of unknown origin in a young cat
- 🚨Progressive weight loss + distended abdomen
- 🚨Neurological signs in a young cat
- 🚨Eye color changes or cloudiness
Frequently Asked Questions
Is FIP contagious to other cats?
Prognosis
Before 2019: 95%+ fatal within weeks to months. With GS-441524 treatment: 80-90% cure rate. Cats successfully completing treatment and observation period are considered cured. Lifelong immunity to FIP appears to develop after recovery.
References
- [1] FIP Warriors — Treatment Guidelines
- [2] UC Davis — FIP Diagnosis and Treatment
- [3] JVIM — GS-441524 Trials
Related Conditions
Feline Panleukopenia (Feline Distemper)
A highly contagious and often fatal viral disease — the feline equivalent of canine parvovirus. Causes severe destruction of white blood cells and intestinal lining. Vaccination is highly protective.
severeFeline Chronic Gingivostomatitis (FCGS)
A severely painful, chronic inflammatory condition of the mouth. Cats develop an exaggerated immune response to dental plaque. Often requires full-mouth tooth extraction for relief.
severeFeline Hepatic Lipidosis (Fatty Liver Disease)
The most common liver disease in cats. Occurs when an anorexic cat mobilizes excessive fat stores, overwhelming the liver. A potentially fatal consequence of a cat not eating. Aggressive nutritional support is lifesaving.
severeFeline Diabetes Mellitus
A common endocrine disorder where the body cannot properly regulate blood sugar. Most cats have Type 2-like diabetes associated with obesity. With proper management, many cats achieve diabetic remission.
moderate