🩺 Peritonitis in Cats – Vet Guide 2025

By Dr Duncan Houston BVSc – Ask A Vet Blog Writer

1. Introduction & Why It Matters

Peritonitis—an inflammation of the abdominal lining—is a serious, often life-threatening condition in cats. It may arise from infection (septic) or internal trauma, or occur as a component of Feline Infectious Peritonitis (FIP), a viral immune-mediated disease. Quick recognition and veterinary care make all the difference.

2. What Is Peritonitis?

Peritonitis involves inflammation of the peritoneum, the tissue lining the abdominal cavity and covering abdominal organs. It can be localized or widespread, septic (infectious) or aseptic (sterile) :contentReference[oaicite:3]{index=3}.

3. Common Causes

3.1 Septic Causes

• Bacterial entry from GI ruptures (e.g., foreign body, ulcer, or tumor) :contentReference[oaicite:4]{index=4}
• Urinary or bile leakage from ruptured bladder or gallbladder :contentReference[oaicite:5]{index=5}
• Post-surgical leakage or penetrating wounds :contentReference[oaicite:6]{index=6}
• Liver abscesses requiring drainage :contentReference[oaicite:7]{index=7}

3.2 Aseptic Causes

• Feline Infectious Peritonitis (FIP)—a mutated coronavirus causing effusion or granulomatous inflammation :contentReference[oaicite:8]{index=8}
• Pancreatitis inducing chemical peritonitis :contentReference[oaicite:9]{index=9}
• Ruptured neoplasia or sterile bile leakage :contentReference[oaicite:10]{index=10}

4. Recognizing the Signs

Clinical signs vary depending on cause:

• Abdominal pain—guarding, vocalisation, tense belly
• Distended abdomen due to fluid (ascites)
• Fever, lethargy, pale gums, rapid breathing, collapse :contentReference[oaicite:11]{index=11}
• Vomiting, diarrhea, and reduced appetite
• Signs of shock—weak pulse, pale mucous membranes

5. Feline Infectious Peritonitis (FIP)

FIP is an often-lethal immune reaction to mutated feline coronavirus. Not all peritonitis cases are FIP; however, it’s a common aseptic cause in young or multi-cat households.

5.1 Forms of FIP

• Wet (effusive): Abdominal or chest fluid accumulation, breathing issues, distended tummy :contentReference[oaicite:12]{index=12}
• Dry (non-effusive): Granulomas in organs—eye and neurologic signs like ataxia, seizures, jaundice :contentReference[oaicite:13]{index=13}
• Many cats show mixed features :contentReference[oaicite:14]{index=14}

5.2 Who's Affected?

• Young cats (3 months–2 years), especially from crowded conditions :contentReference[oaicite:15]{index=15}
• Purebreds, immunocompromised cats, stress-prone environments :contentReference[oaicite:16]{index=16}

5.3 Diagnosing FIP

• Abdominal fluid evaluation—high protein, straw-colored viscous fluid via Rivalta test and cytology :contentReference[oaicite:17]{index=17}
• PCR for viral RNA in effusion :contentReference[oaicite:18]{index=18}
• Blood tests—hyperglobulinemia, low albumin-to-globulin ratio, lymphopenia :contentReference[oaicite:19]{index=19}
• Imaging for organ lesions—ultrasound or CT scanning :contentReference[oaicite:20]{index=20}

5.4 Treating FIP

Until recently, FIP was nearly always fatal—but new antivirals offer hope:

• GS-441524/remdesivir: 80%+ remission in many studies; now legally available in some countries :contentReference[oaicite:21]{index=21}
• GC376: Protease inhibitor with promising but less durable remission :contentReference[oaicite:22]{index=22}
• Molnupiravir: Emerging studies show similar efficacy :contentReference[oaicite:23]{index=23}
• Immunomodulators like feline interferon omega in dry FIP :contentReference[oaicite:24]{index=24}
• Corticosteroids and supportive care—fluids, nutrition, antibiotics for secondary infections

6. Diagnosing Emergency Peritonitis (Septic/Aseptic)

Immediate veterinary attention is essential. Diagnostic steps usually include:

1. Physical exam: Pain, fluid wave, dehydration
2. Blood tests: CBC, biochemistry, electrolytes, coagulation :contentReference[oaicite:25]{index=25}
3. Imaging: X-ray or ultrasound for fluid, free gas, foreign bodies :contentReference[oaicite:26]{index=26}
4. Abdominocentesis: Drain and analyze fluid for appearance, bacteria, cytology, protein :contentReference[oaicite:27]{index=27}
5. Surgery: Exploratory laparotomy to locate and repair GI perforation, bladder/gallbladder rupture, trauma, or drain abscesses :contentReference[oaicite:28]{index=28}

7. Treatment of Non-FIP Peritonitis

Comprehensive treatment includes:

• Hospitalization: IV fluids to combat shock, support electrolytes
• Pain relief: Opioids, NSAIDs carefully monitored
• Antibiotics: Broad-spectrum IV and adjusted by culture results :contentReference[oaicite:29]{index=29}
• Surgery: Correct anatomical defects, remove foreign bodies or necrotic tissue :contentReference[oaicite:30]{index=30}
• Drainage: Abscesses or fluid collections may require drains or percutaneous tapping
• Veterinary ICU care: Monitor vitals, nutrition, wound care through critical phase

8. Recovery & Home Care

• Strict rest & cage confinement to allow healing
• Small frequent meals or feeding tubes if appetite poor
• Careful incision monitoring and cleaning
• Ongoing antibiotic and pain medication administration
• Gradual reintroduction to normal diet and activity as advised by your vet

9. The Role of Ask A Vet, Woopf & Purrz 🛠️

• Ask A Vet: At-home video/chat check-ins to monitor appetite, incision healing, fluid management or fluid wave concerns.
• Woopf: Recovery beds designed for post‑abdominal surgery comfort and cleanliness.
• Purrz: Provides palatable hydrolyzed diets and supplements during convalescence to ease GI stress and support healing.

10. Prognosis

• Septic peritonitis: Prognosis varies: 50–80% survive with prompt surgery and ICU care
• FIP: Once fatal, but antivirals now offer 80%+ recovery in treated cases :contentReference[oaicite:31]{index=31}
• Delayed diagnosis or underlying cancer/trauma worsens outlook

11. When to Contact the Vet Immediately 🚨

• Distended belly, pain, fever, lethargy
• Rapid breathing or shock signs
• Vomiting/diarrhea, blood in vomit or stool
• Appetite loss >24 hours after trauma or surgery

12. Prevention Strategies

• Avoid allowing cats to ingest dangerous foreign bodies
• Promptly treat urinary, GI disease to prevent perforation
• Reduce overcrowding & stress to limit FCoV spread :contentReference[oaicite:32]{index=32}
• Maintain hygiene in multi-cat environments

13. Summary Takeaways

• Peritonitis in cats can be septic (infection) or aseptic (FIP or sterile causes)
• Signs include abdominal pain, fluid, fever, and lethargy
• Diagnosis: fluid analysis, imaging, surgery if needed
• Treatment: fluids, pain control, surgery, antibiotics, antivirals for FIP
• Home care & monitoring are essential—use Ask A Vet, Woopf, Purrz as support

14. Final Thoughts ❤️

Peritonitis is serious—but veterinary advances offer hope for many cats. With swift intervention, targeted treatments, and compassionate home care, recovery is possible. If your cat shows concerning signs, don’t delay—contact your vet or reach out via Ask A Vet for guidance. Your quick action can save lives.