Overview and Prevalence
Feline Infectious Peritonitis (FIP) is a severe, often fatal viral disease caused by a mutation of the feline enteric coronavirus (FECV). While the enteric form is common and usually mild, the mutated virus (FIPV) can trigger an intense inflammatory response. FIP affects cats worldwide, with higher incidence in multi-cat households, shelters, and catteries. Approximately 5-10% of cats infected with FECV develop FIP, and it is most common in cats under 2 years old or over 10 years old. Due to recent advances in antiviral therapy, the prognosis has improved, but traditional treatments remain limited.
Early Warning Signs and Symptoms
FIP presents in two forms: wet (effusive) and dry (non-effusive). Early signs are vague and may include persistent fever (unresponsive to antibiotics), lethargy, decreased appetite, weight loss, and stunted growth in kittens. As the disease progresses, symptoms become more specific:
- Wet form: Accumulation of fluid in the abdomen (distended belly) or chest (difficulty breathing). The fluid is typically straw-colored and thick with high protein content.
- Dry form: Granulomatous lesions in organs (eyes, brain, liver, kidneys). Ocular signs: uveitis (cloudy eyes), vision loss. Neurologic signs: ataxia, seizures, behavioral changes. Jaundice may also occur.
Other signs include diarrhea, vomiting, and in some cases, chronic upper respiratory infections.
Common Causes and Risk Factors
FIP develops from a mutation of feline coronavirus (FCoV). The virus is shed in feces and transmitted via fecal-oral route. Risk factors include:
- Age: Kittens (especially 2-12 months) and older cats are more susceptible.
- Genetics: Purebred cats (e.g., Abyssinian, Bengal, Persian) show increased susceptibility.
- Stress: Overcrowding, rehoming, surgery, or any stressor can trigger mutation.
- Immunosuppression: Concurrent infections (FeLV, FIV) or corticosteroid use increase risk.
- High viral load: Environments with high FCoV shedding (e.g., shelters, catteries).
Not all cats exposed to FCoV develop FIP; the mutation is random and influenced by host immune response.
Prevention Strategies
1. Vaccination: A vaccine exists (intranasal, modified live) but is not routinely recommended due to limited efficacy and short duration. It may be considered for high-risk kittens in endemic areas.
2. Hygiene and Environment: Minimize exposure to FCoV by reducing population density. Use separate litter boxes (one per cat + one extra), clean with bleach solutions (1:32 dilution), and provide proper ventilation.
3. Stress Reduction: Provide hiding spots, vertical space, and stable routines. Avoid sudden changes in environment or diet.
4. Diet and Health: High-quality nutrition supports immune function. Regular deworming and vaccination against other viruses (FeLV, FIV) lower risk.
5. Regular Check-ups: Annual veterinary exams, fecal tests for FCoV, and blood work for at-risk cats can help monitor health.
Diagnostic Process
Diagnosing FIP is challenging due to its variable presentation. A veterinarian will perform:
- Physical exam: Check for fever, abdominal distension, jaundice, ocular changes.
- Blood work: Elevated globulins, low albumin, increased protein, and non-regenerative anemia. A/G ratio <0.8 is suggestive.
- Rivalta test: On effusion fluid (abdomen/chest). A positive result (fluid drops form gel) strongly supports FIP.
- RT-PCR: Detects FCoV RNA in effusion or tissue. A positive result in fluid is diagnostic.
- Immunohistochemistry (IHC): Gold standard on tissue biopsies (but invasive).
- Imaging: X-rays or ultrasound may reveal effusion or organ enlargement.
No single test is definitive; a combination of signs and results from effusion analysis, bloodwork, and PCR is used.
Treatment Options
Historically, FIP was considered fatal. However, recent developments in antiviral drugs have changed the outlook. Treatment includes:
Veterinary Treatment
- Antiviral therapy: GS-441524 (nucleotide analog) and Remdesivir are experimental treatments available through some clinics or clinical trials. They are highly effective (80-90% remission) but require daily injections for 12 weeks and are not FDA-approved.
- Supportive care: Fluid therapy, nutritional support, anti-inflammatory drugs (prednisolone to control inflammation short-term), and appetite stimulants.
Home Care
- Provide a calm, low-stress environment.
- Ensure easy access to food, water, and litter box.
- Monitor weight, temperature, and appetite daily.
- Administer prescribed medications and keep a treatment log.
Common Medications and Treatment
| Drug | Route | Dose | Duration |
|---|---|---|---|
| GS-441524 | Subcutaneous injection | 4-8 mg/kg twice daily (adjust based on response) | 12 weeks minimum |
| Remdesivir | Intravenous (in clinic) | 10 mg/kg loading, then 5 mg/kg daily | 12 weeks |
| Prednisolone | Oral | 1-2 mg/kg twice daily | Short-term (2-4 weeks) to control inflammation |
Note: Antivirals must be prescribed by a veterinarian, often with owner consent for off-label use. Side effects may include injection site reactions and gastrointestinal upset.
When to Seek Emergency Care
Immediate veterinary attention is needed if your cat shows:
- Difficulty breathing (rapid, open-mouth breathing, blue gums).
- Sudden abdominal swelling causing pain or distress.
- Seizures or paralysis (neurologic form).
- Loss of consciousness or collapse.
- Severe depression or inability to eat/drink for more than 24 hours.
These could signal advanced disease or complications.
Prognosis, Recovery, and Long-term Management
Without antiviral treatment, FIP is almost always fatal within weeks to months. With GS-441524 or Remdesivir, about 80% of cats achieve remission. Recovery involves gradual improvement over 2-4 weeks, but full treatment is 12 weeks. Relapse can occur (10-20%), requiring retreatment or dose adjustment. Long-term management includes:
- Regular vet check-ups (every 3-6 months) with blood work and imaging.
- Maintain stress-free environment; avoid boarding or new cats.
- Continue high-quality nutrition and probiotics to support gut health.
- Monitor for signs of recurrence (fever, lethargy, fluid buildup).
Some cats may become long-term carriers of FCoV but never develop FIP again. Others may have residual neurologic deficits or vision loss. Overall, with prompt antiviral therapy, many cats can enjoy a good quality of life for years.