Introduction
Feline Infectious Peritonitis (FIP) was once considered one of the deadliest diseases in cats, leaving owners and veterinarians helpless. For decades, it carried an almost certain death sentence. However, the discovery of antiviral drugs such as GS-441524—marketed in some regions as Pronidesivir (NeoFipronis®)—has revolutionized FIP treatment. Today, thousands of cats are surviving and thriving after what was once a hopeless diagnosis. This article provides a comprehensive overview of FIP: what causes it, how it develops, its clinical signs, diagnosis, treatment, and prevention. The goal is to empower cat owners and veterinary professionals with accurate, science-based knowledge to fight FIP effectively.
1. What Is FIP?
FIP is caused by a mutation of the feline coronavirus (FCoV). While FCoV is common in cat populations and typically harmless—often causing only mild diarrhea—mutations can transform it into a virulent form capable of invading immune cells and spreading throughout the body. This triggers a severe inflammatory response that damages vital organs.
1.1 Epidemiology
Prevalence: In multi-cat households, catteries, and shelters, up to 80–90% of cats may be exposed to FCoV.
Incidence of FIP: Only 5–10% of cats infected with FCoV develop FIP.
Age Risk: FIP is most common in cats under two years of age but can occur at any age.
1.2 Pathogenesis
The disease develops when mutated FCoV infects macrophages (immune cells). Instead of being destroyed, the virus uses these cells to spread, leading to widespread immune-mediated inflammation.
2. Types and Symptoms of FIP
2.1 Wet (Effusive) FIP
Fluid accumulation in the abdomen or chest
Distended belly or difficulty breathing
Fever, weight loss, lethargy
2.2 Dry (Non-Effusive) FIP
Neurological symptoms: seizures, incoordination, paralysis
Ocular symptoms: uveitis, retinal lesions, vision loss
Chronic weight loss, anemia
2.3 Mixed Forms
Some cats exhibit both wet and dry characteristics, complicating diagnosis.
3. Diagnosis
3.1 Why FIP Is Hard to Diagnose
No single test can confirm FIP with 100% certainty. Diagnosis relies on clinical history, supportive evidence, and exclusion of other diseases.
3.2 Diagnostic Tools
Bloodwork: anemia, elevated globulins, low albumin-to-globulin ratio
Imaging: X-rays and ultrasound to detect fluid or organ lesions
Fluid analysis: straw-colored, viscous fluid with high protein content
PCR testing: detects coronavirus RNA; mutation-specific tests improve accuracy
Histopathology: biopsy with immunohistochemistry remains the gold standard
4. Treatment
4.1 Antiviral Therapy
For decades, supportive care was the only option. Now, nucleoside analogues such as GS-441524 have transformed FIP into a treatable disease by stopping viral replication.
4.2 Pronidesivir (NeoFipronis®)
Formulation: veterinary oral tablet
Benefits: avoids painful injections, convenient, increases owner compliance
Efficacy: clinical survival rates exceed 80–90% with proper treatment
4.3 Dosage and Duration
General guideline: ~15 mg/kg/day orally
Neurological/ocular cases may require higher doses
Standard course: 84 days (12 weeks)
Monitoring: routine bloodwork and clinical evaluation
4.4 Supportive Care
Balanced nutrition with taurine, omega-3s, antioxidants
Treat anemia, dehydration, and secondary infections
Use anti-inflammatories or appetite stimulants as needed
5. Prognosis
5.1 Survival Rates
With treatment: over 80% of cats survive, especially wet FIP cases treated early
Without treatment: median survival is weeks to months
5.2 Long-Term Outlook
Many cats achieve full remission. Relapse is possible if treatment is incomplete. Long-term monitoring is recommended.
6. Prevention
6.1 Reducing FCoV Transmission
Keep litter boxes clean and separated
Reduce overcrowding in shelters and catteries
Minimize stress to reduce viral shedding
6.2 Vaccination
An intranasal coronavirus vaccine exists, but effectiveness is controversial and not widely recommended.
6.3 Responsible Cat Care
Screen breeding colonies for high FCoV prevalence
Isolate kittens from infected groups
Maintain good overall health with vaccinations and parasite control
7. Living With and Beyond FIP
7.1 Owner Support
An FIP diagnosis is devastating. Owners face emotional, financial, and ethical challenges. Veterinary guidance and community support are essential.
7.2 Success Stories
Thousands of cats once given no hope are now living healthy lives thanks to GS-441524 treatments. These stories symbolize a turning point in feline medicine.
Conclusion
Feline Infectious Peritonitis is no longer the untreatable disease it once was. Scientific advances, particularly GS-441524-based oral treatments such as NeoFipronis® (Pronidesivir), have given cats worldwide a new chance at life. The key lies in early diagnosis, appropriate treatment, and ongoing monitoring. With continued research and medical progress, the future for cats with FIP is brighter than ever.