Feline infectious peritonitis (FIP) is a rare but life-threatening disease in cats caused by a mutated form of the feline coronavirus. While many cats carry this common virus without ever becoming sick, a small percentage develop FIP, a condition that can progress rapidly and affect multiple organs. For decades, FIP in cats was considered almost universally fatal, leaving guardians with limited options and little hope.
That outlook has begun to change. Recent advances in treatment have significantly improved outcomes and reshaped how veterinarians approach this once-devastating diagnosis.
In this article, we’ll explain what FIP is and why it develops, the symptoms to watch for, why diagnosing FIP in cats can be difficult, and what current treatment options and prognosis look like today. We’ll also touch on prevention and risk reduction, so cat guardians can make informed decisions and act quickly if concerns arise.
What Is FIP in Cats?
According to PetMD, feline infectious peritonitis develops when a cat’s immune system reacts abnormally to a mutated form of feline coronavirus. It is not a typical contagious illness that spreads directly from cat to cat.
Most cats are exposed at some point to feline enteric coronavirus (FeCV), particularly in multi-cat households, shelters, or catteries. In the vast majority of cases, FeCV causes no symptoms at all or only mild, short-lived digestive upset. Rarely, however, the virus mutates inside an individual cat’s body. This mutated version is known as the FIP virus (FIPV).
When this mutation triggers an abnormal immune response, FIP develops. A key point to understand is that cats do not “catch” FIP from one another. The mutation happens within the cat, not through transmission. As a result, most cats that test positive for feline coronavirus will never develop FIP.
Wet FIP in Cats
Wet FIP, also known as the effusive form of feline FIP, develops when an abnormal immune response causes inflammation of the blood vessels. This immune-mediated vasculitis damages the vessel walls, allowing fluid to leak into surrounding body cavities.
Fluid most commonly accumulates in the abdomen or the chest, leading to visible abdominal swelling or breathing difficulties. The fluid itself is not an infection; rather, it is a result of injured blood vessels and ongoing inflammation. Wet FIP tends to progress rapidly, with symptoms appearing suddenly and worsening quickly if treatment is not started.
Because the accumulated fluid has distinctive features, laboratory analysis of this fluid can provide valuable diagnostic clues. For this reason, wet FIP is often easier to recognize and diagnose than other forms of the disease, particularly when compared to non-effusive (dry) FIP.
Dry FIP in Cats
Dry FIP, also called the non-effusive form of feline infectious peritonitis, is characterized by granulomatous inflammation rather than fluid accumulation. In this form of the disease, the abnormal immune response leads to the formation of inflammatory lesions within organs, instead of causing blood vessels to leak fluid.
Dry FIP is more difficult to diagnose because there is little or no free fluid available for analysis. Clinical signs depend largely on which organs are affected, which can make the condition easy to confuse with other diseases. The central nervous system, eyes, liver, and intestines are among the systems most commonly involved.
Compared with wet FIP, dry FIP typically progresses more slowly. Symptoms often develop gradually and can vary widely between cats, which may delay diagnosis and complicate early detection.
Feature | Wet FIP (Effusive) | Dry FIP (Non-Effusive) |
Fluid Accumulation | Yes, in abdomen or chest | No |
Progression Speed | Rapid | Slower, gradual |
Common Symptoms | Abdominal swelling, breathing difficulty | Neurologic signs (seizures, ataxia), eye inflammation, organ-specific symptoms |
Diagnostic Clues | Fluid analysis often helps | Harder to diagnose; relies on organ-specific tests |
Typical Onset | Sudden | Gradual |
How Common Is FIP in Cats?
Feline infectious peritonitis is considered a rare disease, even though exposure to feline coronavirus is extremely common. Research suggests that up to half of cats in single-cat households and as many as 80–90% of cats in multi-cat environments are exposed to feline enteric coronavirus (FeCV) at some point in their lives. Despite this widespread exposure, only a small percentage of cats—estimated at around 5–10% of those infected—will ever develop FIP.
Certain cats are at higher risk. Kittens and young cats under two years of age are more commonly affected, particularly those living in shelters, catteries, or other multi-cat settings where stress and close contact are more likely. Even so, it’s important to keep this risk in perspective: the vast majority of cats that carry or are exposed to feline coronavirus never become sick.
While FIP is a serious and potentially life-threatening condition, it remains uncommon overall, and most coronavirus-positive cats go on to live normal, healthy lives.
How Do Cats Get FIP?
According to the Cornell Feline Health Center, cats are commonly exposed to feline coronavirus through routine daily interactions. The virus spreads primarily via the fecal–oral route, meaning cats may become infected through shared litter boxes, contaminated surfaces, grooming behaviors, or shared food and water bowls.
After exposure, the virus typically remains confined to the intestines and causes either no symptoms or only mild, temporary digestive upset. In a small number of cats, however, the virus later mutates inside the body. This mutated form can trigger an abnormal immune response, leading to the development of FIP. Importantly, this mutation happens within the individual cat and is not transmitted from cat to cat as FIP itself.
The mutation may occur weeks, months, or even years after the initial coronavirus infection. Certain factors appear to increase the risk, including stress, an immature or weakened immune system, genetic susceptibility, and living in crowded environments such as shelters or multi-cat households.
Is FIP Contagious to Other Cats?
FIP itself is not considered contagious. Cats do not pass feline infectious peritonitis directly to other cats. What is contagious, however, is feline enteric coronavirus, which commonly spreads between cats—especially in shared living environments.
Because many cats in the same household may be exposed to feline coronavirus, it is possible for more than one cat to develop FIP. When this happens, it is not due to transmission of FIP from cat to cat. Instead, the virus mutates independently inside each affected cat, triggering the disease separately.
Maintaining good hygiene, keeping litter boxes clean, and minimizing stress can help reduce overall risk. Strict isolation of affected cats is usually unnecessary. Ongoing research continues to explore why these rare mutations occur and why only a small percentage of exposed cats go on to develop FIP.
FIP Symptoms in Cats
According to WebMD, the early symptoms of cat FIP are often subtle and easy to overlook. Many cats develop a persistent fever that does not respond to antibiotics, along with lethargy, weight loss, and a decreased appetite.
As the disease progresses, symptoms can evolve and intensify—sometimes rapidly, other times gradually over weeks or even months. Signs vary widely between cats because FIP can affect different organs and body systems. A cat’s individual immune response, along with which organs are involved, strongly influences how the disease presents and how severe it becomes.
Wet FIP Symptoms in Cats
Wet FIP is the effusive form of the disease and is defined by abnormal fluid buildup in the abdomen, chest, or both. Wet FIP symptoms include a swollen, pot-bellied appearance due to abdominal fluid or show breathing difficulties when fluid accumulates in the chest and restricts lung expansion. This form of FIP usually progresses rapidly. Without treatment, affected cats often worsen quickly, sometimes over days to weeks, and generally decline much faster than cats with dry (non-effusive) FIP.
Dry FIP Symptoms
Dry FIP is the non-effusive form of feline infectious peritonitis, meaning it does not typically involve fluid buildup. Instead, the disease causes inflammation and granulomatous lesions within affected organs. Symptoms vary depending on which organs are involved. Common signs include neurologic issues such as seizures, ataxia (loss of coordination), or head tilt, as well as ocular problems like eye inflammation or vision loss. Because these symptoms are diverse and subtle, dry FIP is often harder to diagnose than wet FIP. The disease generally progresses more slowly, with signs appearing gradually over weeks or months.
FIP Treatment
For many years, FIP was considered almost always fatal. However, FIP treatment has advanced significantly in recent years. Modern antiviral medications, such as GS-441524 and remdesivir, target the virus itself, stopping it from replicating and giving the cat’s immune system a chance to recover. Treatment courses typically last 12 weeks or more, and the drugs can be administered either injectably or orally, depending on the cat’s condition and veterinary guidance.
Supportive care remains important alongside antiviral therapy. This may include fluid drainage for cats with wet FIP, maintaining good nutrition, and anti-inflammatory medications to reduce discomfort. It’s crucial to avoid unregulated or black-market drugs, as these can be ineffective or dangerous. All treatments should be conducted under the supervision of a veterinarian experienced with FIP.
Is FIP Curable?
A diagnosis of FIP can be frightening, as the disease was historically considered almost always fatal. However, recent advancements in treatment have changed the outlook. Modern antiviral therapies, when administered promptly and consistently under veterinary supervision, can allow many cats to recover and enjoy a good quality of life.
Without treatment, FIP often progresses rapidly, sometimes in just days or weeks. Early diagnosis and careful, ongoing therapy greatly improve the prognosis. While research continues and there is still much to learn, there is now genuine hope for cats affected by FIP, and many owners have witnessed their cats recover and thrive.
How to Prevent FIP in Cats
Preventive Measure | Explanation |
Reduce overcrowding | Fewer cats reduces viral spread and stress |
Maintain clean litter boxes | Prevents fecal–oral transmission |
Separate food/water from litter areas | Limits virus exposure |
Minimize stress | Supports immune function |
Vaccination | Limited effectiveness; not routinely recommended |
Regular veterinary care | Ensures early detection and overall health |
There is no guaranteed way to prevent FIP, but certain practices can help reduce the risk. Avoid overcrowding, maintain clean and plentiful litter boxes, and keep food and water separate from litter areas. Minimizing stress is also important for supporting your cat’s immune system.
FIP vaccines are available, but they are not routinely recommended due to limited effectiveness. Focusing on overall health, providing a low-stress environment, and keeping up with regular veterinary care remain the most practical and effective strategies for lowering the risk of FIP.
Conclusion
Feline infectious peritonitis (FIP) is a rare but serious disease caused by a mutated feline coronavirus. While it was once considered almost always fatal, modern antiviral treatments now give many cats the chance for remission. With FIP, cats can experience a range of symptoms, but with early diagnosis and modern antiviral treatments, they can achieve remission and enjoy a better quality of life.
Early detection, consistent veterinary care, and adherence to treatment are critical for improving outcomes. Wet and dry forms of FIP can appear very differently, with symptoms varying depending on the organs affected and the cat’s immune response. Although there is no guaranteed way to prevent FIP, maintaining good hygiene, minimizing stress, and providing supportive care can help reduce the risk.
Frequently Asked Questions
Is FIP painful for cats?
FIP can cause discomfort, particularly if organs are inflamed or if fluid accumulates in the chest or abdomen. The level of pain and other symptoms depends on the form and severity of the disease.
Can a cat with FIP survive?
Yes. With modern antiviral treatments, many cats can go into remission and enjoy long, good-quality lives. Early diagnosis and consistent treatment significantly improve outcomes, though results may vary from cat to cat.
