FIP in Cats: How the Disease Progresses from Infection to Symptoms

Feline Infectious Peritonitis (FIP) is a devastating disease—for both cats and the people who love them.

FIP develops when a common virus known as FCoV (Feline Coronavirus) mutates inside the cat’s body. While most FCoV infections are harmless and symptom-free, trouble begins when this virus changes into its dangerous form.

To protect your cat from this mutation and its life-threatening consequences, it’s crucial to understand how the virus behaves, the symptoms to watch for, and how to respond if you suspect something is wrong.

Here’s the full guide from CureFIP Oceania to help you stay informed and ready.

What Is FIP—and How It Develops from Feline Coronavirus (FCoV)

FIP doesn’t start with a new virus. It’s actually a fatal mutation of the common Feline Coronavirus (FCoV).

This virus is extremely common, especially in:

• Young kittens under two years old

• Cats in shelters, catteries, or multi-cat households

In most cases, cats infected with FCoV appear completely healthy. Their immune systems are strong enough to keep the virus under control.

However, if a cat’s immune system is weakened, the virus may mutate—turning into FIP.

It’s important to know: FIP itself is not contagious. Only the original FCoV can be passed between cats. Whether or not a cat develops FIP depends on factors like age, immune function, stress, and environment.

The Timeline: From FCoV Infection to FIP Symptoms

Stage	Estimated Timeframe
FCoV Exposure	Common in kittens and cats in high-density environments
Incubation Period	Between a few days to 2 weeks
Mutation into FIP	Can occur within weeks or several months
Symptom Onset	Typically 2 weeks to several months after infection

According to research from Cornell University and UC Davis, most cases of FIP appear 2–6 months after the initial FCoV infection. However, in cats experiencing chronic stress, symptoms may take up to a year to develop.

What Affects How Soon FIP Symptoms Appear?

The speed at which FIP symptoms appear depends on multiple internal and external factors:

🐾 Age

Kittens under two years old and senior cats are more susceptible to FCoV—and more likely to experience viral mutation.

🛡️ Immune Strength

The immune system plays a key role. A healthy immune system can suppress the virus. But if defenses are weak, FCoV has a greater chance of mutating into FIP.

💢 Stress

Cats experiencing stress—due to moving homes, vaccination, or surgery—are more likely to undergo FCoV mutation.

🏠 Living Conditions

Cats in overcrowded, unhygienic environments face greater exposure to FCoV and higher mutation risk.

Early FIP Symptoms to Watch For

In its early stages, FIP can resemble other common illnesses. Watch out for:

• Lethargy or reduced activity lasting several days

• High fever that doesn't respond to antibiotics

• Loss of appetite

• Diarrhoea

These signs should prompt immediate veterinary attention, especially if your cat is already at risk.

Advanced (End-Stage) FIP Symptoms

As the disease progresses, symptoms become more severe:

• Extreme fatigue, weakness, excessive sleeping, or hiding

• Rapid weight loss caused by inflammation and lack of eating

• Jaundice, seen as yellowing in the skin, eyes, or gums (due to liver damage)

• Organ failure, often accompanied by vomiting, confusion, and urination issues

Behavioural Changes in Cats with Advanced FIP

In addition to physical signs, you may notice emotional and behavioral changes:

• Hiding or withdrawing from interaction due to pain

• Breathing difficulty, especially with wet FIP (caused by fluid in the chest)

• Increased vocalization, restlessness, or not wanting to be touched

• Dull, damaged coat with heavy shedding and lack of shine

• Difficulty walking due to muscle or joint pain

When to See the Vet: Signs That Require Urgent Action

Bring your cat to the vet right away if you notice:

• A high fever that doesn’t improve after medication

• Sudden weight loss or bloating despite poor body condition

• A refusal to eat, even when offered different meals

• Ongoing fatigue or unusually low energy for multiple days

• Recent contact with a cat known to have FCoV or FIP

Diagnosing FIP involves blood tests, fluid sampling, and sometimes biopsies. Since many of its symptoms overlap with other diseases, early and accurate testing is essential.

Conclusion: The Sooner You Act, the Better the Outcome

FIP is a terrifying diagnosis—but catching it early can make all the difference.

If your cat is diagnosed with FIP, don’t delay. Begin treatment right away using GS-441524, an antiviral medication that has already saved the lives of thousands of cats.

Before starting any treatment, we recommend reaching out to CureFIP Oceania via WhatsApp. Our team can help guide you through proper dosage, care instructions, and ongoing support throughout your cat’s healing journey.