Your Maine Coon isn’t just a pet; they’re a majestic, gentle giant who has completely captured your heart. The thought of them facing a serious illness is terrifying. One of the most feared diagnoses in the feline world is Feline Infectious Peritonitis, or FIP in Maine Coons. For decades, those three letters meant a guaranteed and heartbreaking end.
But things have changed. Radically, and for the better.
If you’re here because you’re worried, or perhaps you’ve just received a suspected diagnosis, take a deep breath. This article is your comprehensive guide to understanding FIP in Maine Coons. We will explain what it is. We will show you how to spot it. Most importantly, we will reveal the incredible new landscape of hope and treatment that exists today.
What is FIP in Cats, and What Causes It?
First, let’s demystify this complex disease. Understanding the cause is the first step to get rid of some fear and misinformation. FIP is not your typical infectious disease; it’s a bit of a biological bad-luck story.
The Feline Coronavirus Connection
The story of FIP begins with a very common and usually harmless virus called Feline Enteric Coronavirus (FCoV). This virus is widespread in the cat population, especially in environments with multiple cats like shelters and catteries. It typically causes, at worst, mild and self-limiting diarrhea.
Most cats—estimates suggest up to 90% in cattery situations—will be exposed to FCoV at some point and develop antibodies. They will live their entire lives perfectly healthy. It’s crucial to understand: Feline Coronavirus is NOT FIP.
The Mutation: When Feline Coronavirus Turns Deadly
So, what causes FIP? FIP occurs when the benign FCoV inside an individual cat’s body undergoes a specific genetic mutation. This mutated virus, now called the FIP virus, gains a terrifying new ability. It can invade and replicate within certain white blood cells called macrophages.
Think of it like this: the original coronavirus is a key that only fits the lock of intestinal cells. The mutation changes the key’s shape, allowing it to suddenly fit the locks of immune cells. This triggers a massive, catastrophic inflammatory response throughout the cat’s body, which is what we recognize as the disease FIP.
Is FIP in Maine Coons Contagious?
This is one of the most common and important questions. The answer is no. The mutated FIP virus is not effectively shed in a cat’s feces, urine, or saliva. It is not considered contagious from one cat to another. Your other cats cannot “catch” FIP from a sick housemate.
However, the underlying, non-mutated Feline Coronavirus (FCoV) *is* highly contagious, primarily through shared litter boxes. FIP is more common in multi-cat households. This is not because FIP itself is spreading. It is because the prerequisite virus, FCoV, is easily shared.
Is FIP Genetic or More Common in Maine Coons?
To be clear, FIP is not a genetic disease in the way that, say, hypertrophic cardiomyopathy (HCM) can be. A cat doesn’t inherit the FIP virus from its parents.
However, evidence suggests that a genetic predisposition to the FCoV mutating may exist. Purebred cats have a higher incidence of FIP than the general mixed-breed population. Breeds like Maine Coons, Abyssinians, Birmans, and Ragdolls are reported to be affected. This might happen because of a less diverse gene pool. This affects the immune system’s response to the initial Feline Coronavirus infection. Stress is also a known trigger for the mutation.
A little deeper into this article you’ll discover the actual incidents of FIP that have occurred in Sassy Koonz kittens. They include their outcomes as well as the parents. You’ll see a pattern that is very obvious.
So, how common is FIP? Overall, it’s still a rare outcome. It’s estimated that only 1-5% of cats infected with the common FCoV will ever go on to develop FIP. While the risk may be slightly elevated for a Maine Coon, it is by no means a certainty.
FIP Symptoms in Maine Coons
FIP’s early symptoms are often vague. They can mimic many other, less serious illnesses. Vigilance is your best tool. The disease generally manifests in two main forms.
The Two Faces of FIP: The Different Types of FIP
FIP is broadly categorized as “wet” or “dry,” although some cats can have a mix of both. The form depends on the type of immune response the cat’s body mounts.
- Wet (Effusive) FIP: This is the more classic and rapidly progressing form. It’s characterized by the accumulation of a sticky, yellow fluid in body cavities. The most common sign is a swollen, fluid-filled abdomen, giving the cat a “pot-bellied” look (ascites). If the fluid builds up in the chest (pleural effusion), it can cause severe difficulty breathing.
- Dry (Non-Effusive) FIP: This form can be even more difficult to diagnose. Instead of fluid, the body forms inflammatory lesions called granulomas on or in various organs. Symptoms are often vague and depend on which organs are affected. Dry FIP can progress more slowly than the wet form.
Early Warning Signs to Watch For
If your Maine Coon seems “off,” don’t dismiss it. Pay close attention to these potential FIP symptoms:
- Persistent Fever: A fever that comes and goes and does not respond to antibiotics is a classic red flag.
- Lethargy and Depression: Your normally playful cat becomes withdrawn, sleeps more, and loses interest in activities.
- Loss of Appetite and Weight Loss: The cat may eat less or stop eating altogether. This can lead to noticeable weight loss and muscle wasting.
- Jaundice: A yellowing tint can appear on the gums, the whites of the eyes, or the skin inside the ears. This indicates liver involvement.
- A Pot-Bellied Appearance: The hallmark of wet FIP.
- Neurological or Ocular Signs (Common in Dry FIP): This can include wobbly gait (ataxia), seizures, and head tilting. There may also be changes in the eyes like inflammation (uveitis) or a change in eye color.
Diagnosing FIP: What Maine Coon Owners Should Know
Here’s a frustrating truth: there is no single, simple blood test that can definitively say “Yes, this is FIP.” Instead, diagnosing FIP is like a detective solving a case. Your veterinarian will gather clues from multiple sources to build a strong, presumptive diagnosis.
What Your Vet Will Look For
If FIP is suspected, your vet will recommend a series of diagnostic tests:
- Bloodwork: A complete blood count (CBC) and chemistry panel are essential. The classic FIP profile shows a low albumin-to-globulin ratio (A:G ratio below 0.4 is highly suggestive), high total protein, non-regenerative anemia, and sometimes high white blood cell counts.
- Fluid Analysis (for Wet FIP): If there is fluid in the abdomen or chest, your vet can take a sample. This procedure is called abdominocentesis or thoracocentesis. FIP fluid is typically a clear to yellow, thick, high-protein liquid. A simple in-clinic test called the Rivalta’s test can strongly support the diagnosis.
- Imaging: X-rays can reveal fluid in the body cavities. More effectively, an ultrasound can show the inflammatory lesions (granulomas) on organs. These lesions are characteristic of dry FIP.
- Definitive Tests: The gold standard for a 100% confirmed diagnosis involves detecting the virus within the macrophages. This is done via immunofluorescence or PCR on the fluid. Alternatively, it can be done more invasively on a tissue biopsy from an affected organ. These tests are often performed once a strong presumptive diagnosis is already in place.
A New Era of Hope: Treatment for FIP
Now for the best part of this article. For decades, the “Treatment” section for FIP would have been a single, somber paragraph about supportive care and humane euthanasia. Not anymore. The world of FIP has been completely revolutionized. There is now FIP medication for cats!
If you or your vet suspect that your cat may have FIP, time is critical. So, you should begin treatment as soon as possible. A couple of days without treatment can mean a matter of life or death.
The Game-Changers: Antiviral Medications
The breakthrough treatment for FIP involves a class of antiviral drugs. The most notable are GS-441524 (an oral medication) and its injectable precursor, Remdesivir. These drugs work by directly interfering with the FIP virus’s ability to replicate, effectively stopping the disease in its tracks.
The standard treatment protocol is a long and demanding one: 84 consecutive days of medication. It requires immense dedication from you as the owner. The medication can be given as a daily injection or, in many cases, as oral pills or capsules. The cure rates are impressive. Studies and community data show rates of 85-90% or even higher.
Navigating the world of these treatments can be complex. These medications are becoming more accessible through veterinarians. However, many owners still rely on online support groups. Groups like the FIP Warriors provide guidance on sourcing and administering the medication. Not all vets are familiar with or able to prescribe this groundbreaking medication yet.
NOTE: In this video he mentions the treatment for FIP being illegal. That has since changed,and now veterinarians are able to prescribe i. (See the other video on this page).
Supportive Care is Key
The antiviral drug is the hero, but it needs a supporting cast. Especially in the early days of treatment, your cat may need additional help, such as:
- Appetite stimulants to encourage eating.
- Anti-inflammatory medications (like steroids) to reduce the severe inflammation quickly.
- Fluid therapy for dehydration.
- Nutritional support with high-calorie, palatable food.
Understanding the Final Stages of FIP (Without Treatment)
It’s difficult to discuss. It’s important to understand what happens if FIP is left to run its course without treatment. This knowledge underscores the urgency of seeking a diagnosis and starting treatment as soon as possible.
In the final stages of FIP, the cat’s body is overwhelmed by the inflammatory process. For a cat with untreated wet FIP, the fluid in the chest can become so severe that they struggle for every breath. This can lead to respiratory failure.
For a cat with dry FIP, the neurological signs can progress to uncontrollable seizures, paralysis, and complete loss of function. In both forms, there is extreme muscle wasting, zero appetite, and a total loss of quality of life.
Seeing a beloved cat in this state is devastating. Before the advent of modern antivirals, the most compassionate choice was humane euthanasia to end their suffering. Today, our goal is to use treatment to ensure a cat never has to reach these final stages.
FIP Instances in Sassy Koonz Maine Coon Kittens
I promised earlier to share the actual number of incidents of FIP in Sassy Koonz kittens. I share this information to be transparent and to set realistic expectations. Getting the news that one of our babies has developed FIP is always devastating.
We started breeding in October 2017 (8 years ago). As of October 31, 2025, Sassy Koonz has produced 270 Maine Coon kittens (average of 33 kittens per year). To date, we have 4 reported cases of FIP in our kittens. That is a total percentage of 1.4%.
FIP Survival Stories: Real Hope for Maine Coon Owners
Two of those kittens were cured from treatment and are doing well. Both of these owners reached out to me immediately. Together, we contacted FIP Warriors to begin the treatment for their kittens. I was kept updated as the owners administered the injections themselves and watched daily improvements. After 84 days, they both were deemed in recovery phase! Both are still doing very well and have not had a relapse.
Unfortunately, One kitten didn’t receive the treatment in time and passed away. The last one received the treatment, was in recession and then had to have unrelated surgery soon after. He did not survive. We think that the immune system was compromised because of the FIP in this case.
We wish that none of our kittens ever have to fight FIP. But if it presents, please contact us immediately so that we can point you in the right direction.
How Sassy Koonz Tracks FIP Cases and Improves Breeding Health
One of the most helpful things we do at Sassy Koonz is track the health and history of every kitten. We rely on the owners to provide us with information every year on annual surveys. Close communication about the cats is highly encouraged as they grow and become more mature. We use this data to make decisions. It helps determine which cats and their offspring are suitable to continue as breeders in our program.
How we handle health issue reports is this: we track which parent the issue came from. The first issue is considered an anomaly and the cats go under close monitoring. If a second similar health issue is reported from the same cat, the cat will retire from our program. It will then become a pet.
With our tracking in place, we were able to link all 4 cases of FIP to the same dad: Beastie. He retired after the second case of FIP was reported.
Out of those 4 kittens, 2 also shared the same mom (Blanche). She also retired after the second report of FIP.
We have had zero instances of FIP since those two cats left our breeding program.
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