Feline Infectious Peritonitis (FIP) is a rare but life-threatening viral disease in cats caused by a mutation of the feline coronavirus. This mutation triggers an excessive immune response, leading to widespread inflammation throughout the cat’s body. Feline infectious peritonitis primarily affects young cats and has historically been considered fatal, but recent treatments are offering new hope.
What is Feline Infectious Peritonitis (FIP) in Cats?
FIP is an immune-mediated disease caused by feline coronavirus infection. Most feline coronaviruses (often called feline enteric coronavirus, FeCV) cause only mild intestinal or respiratory issues, if any. However, in a small percentage of infected cats (approximately 5–10%), the benign virus mutates. It becomes a virulent strain (often called the FIP virus) that can spread throughout the body.
When this happens, the cat’s immune system overreacts to the virus, causing inflammation in blood vessels and organs. The term “peritonitis” refers to inflammation of the peritoneum (lining of the abdominal cavity), which is common in FIP – though the disease can affect many systems, not just the abdomen.
How Do Cats Get FIP?
Cats don’t catch FIP directly from other cats like they would a cold; instead, they first pick up the feline coronavirus (FeCV), typically through the fecal-oral route, such as sharing litter boxes or mutual grooming. This coronavirus spreads rapidly in multi-cat households via feces, saliva, or even sneezes, often causing no symptoms or just mild, temporary issues like diarrhea or sniffles.
The link between cats and FIP emerges only when FeCV spontaneously mutates inside an individual cat, transforming into the deadly feline infectious peritonitis virus (FIPV), a rare, idiosyncratic event akin to a genetic error that allows the virus to invade organs and trigger systemic disease.
While the precise trigger remains unknown, factors like the virus strain, the cat’s genetics, immune status, age, and stressors (e.g., overcrowding) can influence whether this mutation occurs and progresses to FIP in one cat but not another.
Types of Feline Infectious Peritonitis
Veterinarians recognize two main forms of FIP: wet FIP (effusive form) and dry FIP (non-effusive form), based on how the cat’s immune system responds to the virus.
Wet FIP in cats, which makes up about 80% of cases, involves fluid buildup in the abdomen or chest and often progresses quickly, causing a swollen belly or breathing difficulty.
Dry FIP (non-effusive form) does not cause fluid accumulation but leads to inflammatory lesions in organs such as the liver, kidneys, eyes, or brain, resulting in more gradual and varied symptoms.
What are the Signs and Symptoms of FIP in Cats?
Early FIP symptoms in cats are often vague and nonspecific, including:
- Lethargy
- Reduced appetite
- Weight loss
- Dull or unkempt coat
- Persistent fever that doesn’t respond to antibiotics
- Some cats may show mild sneezing, watery eyes, or diarrhea during initial coronavirus infection, which may resolve.
FIP can develop weeks to months later, after these early signs. As the disease progresses, signs differ based on the type of FIP:
Wet FIP
- Fluid buildup in the abdomen (ascites), causing a swollen or “pot-bellied” appearance
- Fluid in the chest leading to rapid or difficult breathing, panting, or open-mouth breathing
- High fever, weakness
- Pale or bluish gums if oxygen levels are affected
- Progresses rapidly over days to weeks
Dry FIP
- Slower progression with ongoing fever, lethargy, poor appetite, and weight loss
- Granulomas form in organs, leading to organ-specific signs:
- Liver/kidneys: jaundice, increased drinking and urination
- Eyes: redness, cloudiness, bleeding, or pus (uveitis)
- Nervous system: wobbliness, head tilt, loss of balance, seizures
- Signs may appear in any combination and worsen steadily without treatment
If your cat shows sudden breathing difficulty, fluid buildup, or rapid decline, seek pet emergency care near you immediately.
How Veterinarians Diagnose Feline Infectious Peritonitis
FIP is difficult to diagnose because there is no single definitive test. A positive feline coronavirus antibody test only confirms exposure, not FIP. Some cats with FIP may have low antibody levels due to immune system exhaustion. This can sometimes lead to false-negative test results, meaning the test appears normal even though the cat is actually sick. This happens because the immune system is no longer producing enough detectable antibodies, especially in advanced disease.
Diagnosis is often presumptive, based on the overall clinical picture.
Common diagnostic steps include:
- Detailed history and physical examination
- Blood tests
- Imaging (X-rays or ultrasound)
- Analysis of abdominal or chest fluid (if present)
Bloodwork findings that support FIP:
- High total protein levels
- Increased globulins
- Low albumin-to-globulin (A:G) ratio (typically < 0.8)
Fluid analysis findings (wet FIP):
- Yellow-tinged, thick fluid
- High protein, low cell count
- Positive Rivalta test (supportive but not definitive)
Advanced tests:
- PCR or immunostaining to detect the FIP virus
- May produce false positives or negatives
Definitive confirmation often requires tissue examination (histopathology), which is not always practical in sick cats. In practice, vets assess multiple factors together, such as young age, persistent fever, abnormal blood results, and fluid accumulation, to reach a likely diagnosis.
Accurate diagnosis of FIP starts with a thorough clinical evaluation at a pet clinic near you.
Treatment of Feline Infectious Peritonitis (FIP):
Until recently, FIP was considered almost always fatal, with only comfort-focused care available.
Feline infectious peritonitis treatment has changed with antiviral drugs. These antivirals stop viral replication and have shown high survival and cure rates in many FIP cats.
Treatment details:
- Antiviral medicines are usually given for at least 12 weeks
- They are administered orally or by injection, depending on the formulation
- Their dose depends on body weight and whether the brain or eyes are involved
- The treatment must be supervised by a veterinarian
Availability:
- Accessible through veterinarians
- Remdesivir is used off-label in cats in some regions
- Treatment can be costly and requires strict adherence to the full course
Supportive care alongside antivirals may include:
- Draining chest or abdominal fluid when needed
- IV fluids for hydration
- Nutritional support or appetite stimulants
- Corticosteroids are used in select cases to reduce inflammation
- Antibiotics are only used if secondary bacterial infections are suspected
For surgical interventions associated with FIP management, schedule or inquire at pet surgeries near you.
How to Prevent FIP in Cats
Preventing FIP focuses on reducing feline coronavirus exposure, as FIP cannot develop without it.
Reduce Stress and Overcrowding:
- In multi-cat Indian households, limit numbers to what your space allows (e.g., 3-5 cats max in small apartments) and rotate play areas to give each cat downtime.
- For shelters, catteries, or stray colonies, prioritize basic partitioning with affordable dividers (like cardboard or nets) and staggered feeding to minimize (direct & indirect) contact.
- Maintain a calm, low-stress environment to support immunity
Hygiene and Litter Box Management:
- Use clumping scoopable litter
- Scoop litter boxes daily
- Provide one litter box per cat, plus one extra
- Keep litter areas separate from food and water
- Regularly disinfect litter boxes, bowls, bedding, and toys
Isolate New Arrivals:
- Strictly separate new cats or kittens in multi-cat homes
- Use separate litter boxes for new kittens and cats
- Do not get another cat if you have a FIP-positive cat
Recovery and Management of Feline Infectious Peritonitis
Managing FIP requires commitment, but recovery is now possible with antiviral treatment. Cats are typically treated for about 12 weeks, followed by an observation period of 8–12 weeks to monitor for relapse.
During this time, vets closely track weight, appetite, activity, and blood parameters. Cats that remain symptom-free after monitoring are considered cured and often return to a normal quality of life, though periodic vet check-ups are still advised.
Supportive care remains important during recovery, including good nutrition, appetite support if needed, a calm, low-stress environment, and targeted care for lingering eye or neurological issues.
Without treatment, FIP is usually fatal; wet FIP progresses over days to weeks, and dry FIP over weeks to months, so pursuing treatment early makes a critical difference.
At What Age is a Cat Most at Risk of Developing FIP?
FIP mainly affects young cats. Around 70% of cases occur under 1.5 years old, especially in kittens under 7 months. There’s also a smaller risk spike in senior cats, due to weaker immunity.
Are Other Cats in the Household at Risk?
Most exposed cats won’t develop FIP unless they are immunocompromised or infected with FeLV. Still, practice good hygiene, clean litter boxes daily, separate food/water from litter, and avoid adding new cats during or soon after an FIP case.
FAQs
What are the first signs of FIP in cats?
The early signs of FIP are often vague and easy to miss. Cats may seem generally unwell, with lethargy, poor appetite, and weight loss or poor growth in kittens. A persistent fever that doesn’t respond to antibiotics is a key warning sign.
Can a cat with FIP survive?
Yes, a cat with FIP can survive and even be cured with prompt antiviral treatment. Antiviral meds have dramatically improved outcomes, especially when treatment starts early and the full course is completed. Without treatment, FIP is usually fatal, so early veterinary care is critical.
How do indoor cats catch FIP?
Yes, indoor cats can develop FIP if they were exposed to feline coronavirus earlier in life, often before adoption from breeders, shelters, or multi-cat homes. The virus spreads mainly through shared litter boxes and contaminated surfaces.
What causes a cat to have FIP?
FIP occurs when a common feline coronavirus mutates inside a cat and triggers an abnormal immune response. The immune system’s reaction causes inflammation, fluid buildup, and tissue
damage. Factors like age, genetics, stress, and immune health influence this process.
How Does a Cat Become Infected with Feline Coronavirus?
Most cats catch feline coronavirus through the fecal-oral route, typically from contaminated litter boxes or grooming after contact with infected feces or saliva. It can also spread via shared bowls or close contact.
How long does a kitten live with FIP?
Without treatment, FIP progresses quickly; wet FIP often leads to complete collapse within days to weeks, and dry FIP within weeks to a few months. With prompt antiviral treatment, many kittens can recover fully and go on to live a normal lifespan. Early diagnosis and treatment significantly improve survival chances.
References:
Cornell University College of Veterinary Medicine. (n.d.). Feline infectious peritonitis (FIP). Cornell Feline Health Center. Retrieved from https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/feline-infectious-peritonitis
Pedersen, N. C. (2009). A review of feline infectious peritonitis virus infection: 1963–2008. Journal of Feline Medicine and Surgery, 11(4), 225–258. https://doi.org/10.1016/j.jfms.2008.09.008
VCA Animal Hospitals. (n.d.). Feline infectious peritonitis. Retrieved from https://vcahospitals.com/know-your-pet/feline-infectious-peritonitis
Addie, D. D., Belák, S., Boucraut-Baralon, C., Egberink, H., Frymus, T., Gruffydd-Jones, T., … & Horzinek, M. C.(2009). Feline infectious peritonitis. ABC Guide to Cat Infectious Diseases, European Advisory Board on Cat Diseases (ABCD). Retrieved from https://www.abcdcatsvets.org/feline-infectious-peritonitis/UC Davis School of Veterinary Medicine. (n.d.). Feline coronavirus and FIP. Retrieved from https://www.vetmed.ucdavis.edu/hospital/small-animal/internal-medicine/feline-infectious-peritonitis
