What Is FIP in Cats?
FIP in cats is a systemic inflammatory disease caused by a specific mutation of the feline coronavirus. Until 2019 it was considered incurable. Today, with the right treatment, more than 92% of treated cats overcome the disease.
The feline coronavirus and the mutation that causes FIP
The feline coronavirus (FCoV) is an extremely common virus in the cat population, particularly in multi-cat households or colonies. The majority of cats infected with FCoV develop no serious symptoms — the virus circulates through the intestinal tract and the immune system controls it without difficulty.
The problem arises when the virus mutates. In a small percentage of infected cats, the FCoV undergoes a mutation that allows it to replicate inside macrophages — immune cells that normally fight infections. This mutated version of the virus triggers a massive, uncontrolled inflammatory response, and that response is what causes FIP.
The key point: this mutation is not hereditary or predictable. You cannot know in advance which cat will develop FIP. And while FCoV can spread between cats via the fecal-oral route, FIP itself does not spread directly from one cat to another.
Types of FIP
Wet FIP (effusive)
The most common form. Characterized by fluid accumulation in the abdomen (ascites) or chest (pleurisy). The cat develops a progressively distended abdomen.
Dry FIP (non-effusive)
More difficult to diagnose. Inflammatory granulomas affect internal organs, eyes, or nervous system. May manifest as eye problems, neurological signs, or progressive kidney failure.
Mixed form
Some cats show a combination of wet and dry signs. It is possible for wet FIP to evolve toward a dry form during treatment, which generally indicates a positive response to antivirals.
What does the diagnosis mean for my cat?
It means your cat is sick — and needs treatment as soon as possible. But it does not mean the situation is hopeless.
Before 2019, a FIP diagnosis was practically a sentence of euthanasia. Today, with GS-441524 or other antivirals, the cure rate exceeds 92%. Cats that complete the 84-day treatment and the subsequent monitoring period largely go on to live completely normal lives.
The diagnosis is the first step toward the cure, not the end of the road.
FAQ
Questions about FIP
Clear answers to the most common questions.
It is estimated that between 5% and 10% of cats infected with feline coronavirus (FCoV) develop FIP. The vast majority of cats carrying the coronavirus never develop the disease. Factors that may favor the mutation include stress, a compromised immune system, and living in large groups of cats.
Yes, though FIP most commonly affects young cats (especially those under 2-3 years) and older cats with weakened immune systems. Cats between 6 months and 3 years represent the majority of diagnosed cases, but the disease can occur at any age.
No. The feline coronavirus (FCoV) and SARS-CoV-2 (the virus causing COVID-19 in humans) are distinct viruses from the same family. FCoV does not affect humans, and SARS-CoV-2 does not cause FIP in cats. There is no cross-species transmission risk in this case.
Does your cat have FIP?
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