Causes of FIP: The Feline Coronavirus Connection

Feline Infectious Peritonitis (FIP) is a devastating disease in cats, long considered a death sentence until recent breakthroughs in antiviral treatment like Molnupiravir (molnupiravir). Caused by a mutation of a common virus, FIP affects cats worldwide and presents in two primary forms: wet (effusive) and dry (non-effusive). But what causes this fatal illness?

At its root, FIP originates from the feline coronavirus (FCoV) — a generally harmless virus found in multi-cat environments. This article explores how a common virus can mutate into a deadly disease, who is most at risk, and how cat parents can reduce the likelihood of infection.

What is Feline Coronavirus (FCoV)?

Feline coronavirus (FCoV) is not the same as the human coronavirus (SARS-CoV-2). It is a species-specific virus that primarily infects the cats' gastrointestinal tract. Most FCoV infections are either asymptomatic or cause mild diarrhea. It is highly contagious, especially in multi-cat households, shelters, or catteries, and is transmitted through:

• Fecal-oral contact (shared litter boxes)

• Contaminated food dishes or grooming

• Sneezing or nose-to-nose contact (less common)
  

Prevalence: According to Cornell University and the American Association of Feline Practitioners (AAFP), up to 80–90% of cats in multi-cat environments may carry FCoV at some point.

How FCoV Mutates Into FIP

In most cats, FCoV causes no lasting harm. However, in 5–10% of infected cats, the virus mutates within the body into a more aggressive form — one that can invade white blood cells and spread systemically. This is when FIP develops.

The Mutation Process:

• FCoV mutates in the gastrointestinal tract.

• The mutated virus gains the ability to infect macrophages (a type of white blood cell).

• Infected cells carry the virus throughout the body, causing widespread inflammation.

• Depending on which organs are most affected, cats develop wet FIP, dry FIP, or neurological/ocular FIP.
  

This mutation is not contagious — only the original FCoV can spread between cats.

Risk Factors for FIP Development

Not every FCoV-positive cat will develop FIP. The development of the disease depends on several factors:

1. Age

FIP is most common in kittens under 2 years and senior cats due to weaker immune systems.

2. Immune System Status

Cats with compromised immunity (e.g., from FeLV, FIV, or stress) are more vulnerable.

3. Genetics

Certain purebred cats (Birmans, Ragdolls, Bengals) show a higher genetic predisposition to FIP.

4. Stress and Environmental Factors

Stress from rehoming, surgery, overcrowding, or illness can trigger the mutation.

5. High FCoV Viral Load

Cats exposed to high quantities of FCoV (common in shelters or catteries) are at increased risk.

Common Myths vs. Facts

There are many misconceptions about FIP. Let’s separate myths from evidence-based facts:

Myth	Fact
FIP is contagious to other cats	❌ False – FCoV is contagious, not FIP. The mutation is internal.
Only outdoor cats get FIP	❌ False – Indoor cats in multi-cat homes are also at risk.
There’s no hope after diagnosis	❌ Outdated – Molnupiravir-based antivirals like MolnuFIP have saved thousands of lives.
All FCoV-positive cats get FIP	❌ Only a small percentage of FCoV carriers develop FIP.

Preventing Coronavirus Spread in Cats

While you can't always prevent FCoV infection, you can reduce the risk of FIP development with good hygiene and stress management:

✅ Litter Box Management

• Scoop litter boxes daily

• Provide one box per cat + one extra

• Place litter boxes far from food and water
  

✅ Cleanliness and Disinfection

• Clean shared food/water bowls regularly

• Disinfect surfaces with cat-safe cleaners
  

✅ Reduce Stress

• Avoid overcrowding

• Allow new cats to acclimate gradually

• Maintain a predictable routine
  

✅ Regular Vet Checkups

• Monitor for weight loss, fever, or behavior changes

• Test for FCoV in high-risk populations if needed
  

✅ Breeder and Shelter Responsibility

• Screen breeding cats for FCoV

• Avoid early weaning

• Maintain small group housing when possible
  

Conclusion

Feline Infectious Peritonitis is caused by an unfortunate twist in the tale of a common virus — the feline coronavirus. While FCoV is widespread and often harmless, its mutation into FIP can be fatal without early intervention.

Thanks to modern antivirals like MolnuFIP (molnupiravir), FIP is no longer a death sentence. Understanding the cause, transmission, and prevention of FIP empowers cat parents and professionals alike to act early and save lives.

If your cat has tested positive for FIP or is showing suspicious symptoms, don’t wait. Visit MolnuFIP to speak with a specialist, learn about treatment, and find compassionate support for your cat’s recovery.