La FIP (Feline Infectious Peritonitis) was for decades considered incurable. Fatal. Terrifying for every cat owner. Today, thanks to new medications, FIP can be cured. The revolution of recent feline veterinary medicine.

What Is FIP

Definition

A serious viral disease in cats:

  • Caused by a mutation of the feline coronavirus
  • Multifactorial
  • Often affects young cats

Feline Coronavirus (FCoV)

An important distinction:

  • "Common" FCoV: a harmless virus, present in many cats
  • Mutated FCoV (FIPV): causes FIP in some cats

The virus mutates within the same cat — it does not spread as FIP.

Transmission

Common Coronavirus (FCoV)

Yes, it is contagious:

  • Faeces
  • Fomites (shared litter boxes)
  • Common in catteries and breeding facilities
  • 30–90% of cats in group settings are "carriers"

FIP

It is NOT directly contagious:

  • Only the virus mutates within the same cat
  • Housemates of a cat with FIP do not "catch FIP"
  • They may contract the common coronavirus

Types of FIP

"Wet" Form (Effusive)

More common:

Symptoms

  • Fluid accumulation in the abdomen (swollen belly)
  • Or in the chest (breathing difficulties)
  • Lethargy
  • Anorexia
  • Persistent fever

Course

Rapid: 2–8 weeks without treatment.

"Dry" Form (Non-Effusive)

Less common:

Symptoms

  • Granulomatous lesions in organs
  • Variable symptoms (depending on the organ involved)
  • Ocular lesions (uveitis)
  • Neurological symptoms (in some cases)

Course

Slower: weeks to months.

Specific Symptoms

Systemic (Always Present)

  • Persistent fever (40°C+, does not respond to antibiotics)
  • Anorexia
  • Weight loss
  • Lethargy

Wet Form

  • Swollen abdomen, a hallmark sign
  • Breathing difficulties (if the chest is involved)
  • Visible distension

Dry Form

  • Ocular lesions (uveitis, change in iris colour)
  • Neurological symptoms (ataxia, paresis, seizures)
  • Jaundice (yellowing of the eyes and mucous membranes)
  • Enlarged lymph nodes

At-Risk Cats

Age

Most commonly affected:

  • 4 months – 3 years (90% of cases)
  • Peak at 6–18 months

Rare in mature adult cats.

Genetics

Familial predisposition is possible.

Most Affected Breeds

Statistics show:

  • Birman
  • Abyssinian
  • Bengal
  • Himalayan
  • Persian

Specific genetic lines.

Triggering Factors

  • Stress (moving house, a new cat, separation)
  • Overcrowding (catteries, breeding facilities)
  • Compromised immune system
  • Heavy exposure to coronavirus

Diagnosis

Challenging

No single definitive test exists:

Tests

Blood Tests

  • Anaemia
  • Elevated globulins (A/G ratio < 0.8)
  • Elevated bilirubin
  • Lymphopaenia

PCR Test

  • On blood (not very reliable)
  • On fluid (more reliable in the wet form)

Fluid Analysis

In the wet form:

  • Fluid aspiration
  • Straw-yellow colour
  • High protein levels (above 4 g/dL)
  • Positive Rivalta test

Biopsy

Definitive but invasive.

Differential Diagnosis

Distinguish from:

  • Heart failure (cardiac effusions)
  • Tumours
  • Other infections

Treatment: The GS-441524 Revolution

What It Is

An antiviral drug developed by Gilead Sciences:

  • Originally developed for Ebola in humans
  • Shown to be effective against FIP in cats
  • A definitive cure

Timelines

Treatment

  • 84 days (12 weeks)
  • Daily injections (or oral tablets)
  • Specific regimens may apply

Recovery

  • Response begins within 2–7 days
  • Dramatic improvement within 2 weeks
  • Full recovery in 12 weeks

Recovery Rate

85–95% of cats treated with GS-441524.

Availability

A Complex History

  • 2019: efficacy discovered
  • 2020–2022: "grey" market (unapproved drug)
  • 2023–2024: first approvals in some countries
  • 2024–2025: growing availability

In Italy

  • Available through specialist veterinarians
  • High cost but curative
  • Check with your veterinarian

Costs

  • Full treatment: €3,000–€8,000
  • Variable depending on the cat's weight

Side Effects

Generally well tolerated:

  • Pain at the injection site (occasional skin lesions)
  • Mild gastrointestinal upset
  • Transient lethargy

Before the Revolution

"Old" Therapy

Before GS-441524:

  • Corticosteroids (palliative)
  • Antibiotics for secondary infections
  • Fluid drainage
  • Euthanasia was often the chosen path

Life expectancy: 2–12 weeks.

Early Diagnosis

Essential

The earlier the diagnosis, the greater the chance of success:

Warning Symptoms

  • Persistent fever in a young cat
  • Lethargy combined with anorexia
  • Swollen belly
  • Ocular lesions

→ Seek urgent veterinary attention.

Early Tests

  • Blood tests
  • Coronavirus PCR
  • Ultrasound/X-ray if indicated

Prevention

Reducing Exposure to Coronavirus

Even though the common coronavirus does not directly cause FIP, reducing exposure lowers the risk of mutation:

Catteries/Breeding Facilities

  • Rigorous litter box hygiene
  • Multiple litter boxes
  • Disinfection

Home

  • One litter box per cat, plus one extra
  • Daily cleaning
  • Quarantine for new arrivals

Vaccination

Is There a Vaccine?

Yes, but it is controversial:

  • Intranasal vaccine (Felocell)
  • Limited efficacy (50–75%)
  • Not always recommended
  • Available in some countries

Stress Reduction

Stress = a trigger:

  • Predictable routines
  • A calm environment
  • Avoid traumatic changes

Cats That Have Been Cured

Life After FIP

Cats treated with GS-441524:

  • Lead a normal life
  • Have a standard life expectancy
  • May still carry the common coronavirus
  • Will not develop FIP again (in most cases)

Follow-Up

  • Blood tests every 3–6 months (first year)
  • Annually thereafter

The Current Situation (2026)

Availability

  • USA, UK: GS-441524 widely available
  • Italy: through specialist veterinarians
  • Regulatory approvals ongoing

Specialist Clinics

In Italy, clinics experienced in FIP:

  • Veterinary universities
  • Centres of excellence
  • Up-to-date veterinarians

Alternative Drugs

  • Molnupiravir (originally for COVID-19): effective
  • Remdesivir: an alternative
  • Bovine interferon: limited

Lifetime Costs

Diagnosis

  • Consultations + tests: €300–€600
  • PCR + fluid analysis: €200–€400

GS-441524 Treatment

  • 12 weeks: €3,000–€8,000
  • Possible hospitalisation: €500–€2,000

Recovery

  • Follow-up tests: €200–€400

Overall total: €4,000–€11,000.

Alternatives

Euthanasia with anaesthesia: €100–€200.

For many families:

  • A difficult decision based on:
    • Cost
    • The cat's age
    • Availability of treatment
    • Personal ethics

Common Myths

"FIP Is Contagious"

False. The common coronavirus is — FIP is not.

"All Cats with Coronavirus Will Develop FIP"

False. Only 5–10% of cats with coronavirus develop FIP.

"FIP Is Always Fatal"

Once true, today false. GS-441524 cures 85–95% of cases.

"It Can Be Transmitted to Humans"

False. Feline coronaviruses are species-specific and do not infect humans.

Cat Situations

Single Cat in the Household

  • Lower risk (less coronavirus exposure)
  • Quarantine for new arrivals is important

Multi-Cat Households

  • Higher risk
  • Good hygiene reduces coronavirus transmission
  • Never panic if one cat develops FIP (the others may be absolutely fine)

Breeding Facilities

  • Genetic predispositions
  • Bloodlines to consider
  • Coronavirus management is essential

What to Do If You Suspect FIP

Step 1: Specialist Veterinary Consultation

Not a general practitioner. Look for:

  • Feline internal medicine specialists
  • University veterinary centres

Step 2: Differential Diagnosis

Rule out other conditions:

  • Symptoms similar to tumours, organ failure, etc.

Step 3: Planning

If FIP is confirmed:

  • Discussion of options
  • Costs and benefits
  • Family decision

Step 4: Treatment

With GS-441524 when available.

Hope

A Shift in Thinking

From 2020 onwards:

  • FIP is no longer a "death sentence"
  • A cure is available
  • Life expectancy has been restored

Success Stories

Thousands of cats cured around the world:

  • Normal life afterwards
  • Standard life expectancy
  • A veterinary revolution

In Summary

Feline FIP — Feline Infectious Peritonitis — is caused by a mutation of the feline coronavirus. For decades it was fatal. Today, GS-441524 is a cure with an 85–95% success rate. The cost is significant (€3,000–€8,000) but it is curative. Symptoms include persistent fever, a swollen belly, ocular lesions and neurological signs. Young cats (4 months – 3 years) are most commonly affected. Early diagnosis is essential. It is no longer a death sentence. If your cat is suspected of having FIP, seek a specialist veterinarian immediately. There is hope.