Feline Infectious Peritonitis (FIP) in Cats 🐱🧬

By Dr Duncan Houston, BVSc

Feline Infectious Peritonitis (FIP) is a serious and historically fatal disease caused by a mutated feline coronavirus. It progresses quickly, often in young cats, and affects multiple organs. But in 2025, there’s renewed hope: new antiviral treatments are saving lives. 🧪

🔍 What Causes FIP?

FIP begins as a common feline coronavirus (FCoV) infection. Most cats experience only mild gastrointestinal upset or no symptoms at all. However, in rare cases, the virus mutates inside the cat’s body and becomes FIP virus (FIPV), a deadly form that targets internal organs. 🦠

Important:

• 😺 Feline coronavirus is extremely common, especially in multi-cat households
• 🔬 FIP mutation is rare and not directly contagious
• 🚫 FIPV is not easily spread between cats

⚠️ Two Forms of FIP

1. 💧 Effusive (Wet FIP)

• 🫁 Fluid in chest, abdomen, or around the heart
• 🐱 Enlarged belly, breathing issues
• 🌡️ Fever, weight loss, poor appetite

2. 🌪️ Non-effusive (Dry FIP)

• 🧠 Neurological signs—wobbly walking, seizures
• 👁️ Eye issues—vision loss, inflammation
• 🧫 Granulomas in organs like liver, kidneys

Some cats may shift between wet and dry forms. Early detection is key. 🧠

🧪 How Is FIP Diagnosed?

FIP diagnosis is tricky—there’s no single definitive test. Instead, veterinarians use a combination of:

• 💉 Bloodwork for inflammation or organ damage
• 💧 Fluid analysis from chest or abdomen
• 🧬 PCR or antibody testing (may be false positive if cat has regular coronavirus)
• 📸 X-rays or ultrasound for fluid or masses

Often, diagnosis is presumptive—based on symptoms and rule-outs. Some confirmed cases are only diagnosed post-mortem. 😢

💊 Breakthrough Treatments

Great news: FIP is no longer a guaranteed death sentence. Two antiviral medications have shown strong promise:

1. 💉 GS-441524

• 🔬 A nucleoside analog that stops viral replication
• 🧪 Derived from research on Remdesivir
• 🧴 Available via compounding pharmacies in the U.S.
• 📈 Many cats show dramatic improvement within days

2. 💊 Remdesivir

• 💉 Antiviral drug used in COVID-19 treatment
• 🧬 Converted into GS-441524 in feline bodies
• 💲 Often used where GS is hard to obtain

⚠️ Important Notes:

• 💵 Treatment is expensive—can run into thousands
• 📆 Full course usually 12–16 weeks
• 🧪 Not FDA-approved but permitted for vet use due to lack of alternatives

Ask your vet about treatment access, costs, and support programs. Early treatment improves success. ❤️

🩺 Supportive Care

• 💧 IV fluids for dehydration
• 🍲 Nutritional support
• 🧼 Periodic draining of abdominal/chest fluid
• 💊 Corticosteroids like prednisolone (not curative)

Without antivirals, comfort care and humane euthanasia may be the kindest choice. 😿

🛡️ Can FIP Be Prevented?

Since the mutation from FCoV to FIPV is spontaneous, it can’t be fully prevented—but you can reduce risk:

• 🚽 Clean litterboxes daily
• 🧼 Minimize fecal contamination in multi-cat homes
• 😺 Reduce stress and crowding
• 🔍 Test & isolate high-shedding cats

💉 A vaccine exists but is largely ineffective and not routinely recommended.

📱 Ask A Vet App Support

Think your cat may have FIP? The Ask A Vet app can help you take action fast:

• 📸 Upload symptoms and videos for triage
• 💬 Get help discussing GS-441524 or Remdesivir access
• 🧾 Receive personalized treatment plans
• 📊 Track weight, energy levels & medication dosing

🏁 Final Takeaway

FIP is serious—but not always fatal. New antivirals are changing outcomes. If your cat shows signs, don’t wait. Early treatment matters. Consult your vet, and use Ask A Vet for quick answers, access, and support. 🐱🧬❤️