FIP in Cats: Symptoms and Treatment

Dr. Jason Gagné, DVM, DACVIM
By Dr. Jason Gagné, DVM, DACVIM
Updated: 5/20/20242-4 minutes
owner holding white cat

What is FIP (Feline Infectious Peritonitis) in Cats?

FIP is a relatively rare but often fatal viral disease which is common in young cats (less than two years old) and kittens and is caused by an infection with the virus named feline coronavirus. It’s important to note that this is different from the coronavirus that infects people and leads to COVID-19. This is a feline coronavirus that is very common and only causes mild symptoms, but in a few cases, it mutates into the feline infectious peritonitis virus, triggering FIP, a serious disease that is deadly for most cats.

A mutated feline coronavirus can trigger feline infectious peritonitis, so before we get to the specifics of the FIP disease in cats, let’s look at what the feline coronavirus is and how your cat might get it.

What is FIP in Cats?

Feline infectious peritonitis (FIP) is a viral disease caused by a feline coronavirus. It affects cats and is not contagious to humans. However, FIP is contagious to other cats and is usually passed in cat feces. This is why it’s more common in cats that are in close proximity or share a household with other cats and are in contact with their litter boxes.

The good news is that, despite being a very contagious virus encountered by nearly every cat throughout their lives, feline coronavirus doesn’t typically make your cat visibly ill. The infection is normally limited to the intestinal tract, so if FIP symptoms do manifest, they’re mild and you will usually notice your kitten suffering from diarrhea for a few days and nothing more.

Why Does Feline Coronavirus Cause Feline Infectious Peritonitis?

So how does a seemingly harmless virus turn into a more dangerous strain, capable of activating a disease that is fatal for most cats? As the feline coronavirus starts to replicate inside your cat’s body, mutations might occur. Scientists don’t know yet what is causing these mutations, but a weak immune system, stress, and even age (with younger cats being more susceptible to FIP virus) have been proposed as possible explanations.

One of these mutations can turn the feline coronavirus into the feline infectious peritonitis virus which, instead of remaining confined to the intestinal tract, infects blood cells that then travel throughout the entire body. The immune system should be able to intervene at this point and fight off the infection, but if this does not happen, the cat will develop FIP.

So, even if the cat becomes infected with the FIP virus, it does not necessarily follow that they will suffer from the FIP disease. A strong immune system will be able to prevent the illness from being triggered. However, this means that young and old kittens with weaker immune responses are less likely to stop the virus and FIP will be triggered. Despite this, the disease luckily remains quite rare in cats.

What Are the Symptoms of FIP in Cats?

Unfortunately, FIP in cats can’t be easily recognized through symptoms alone. The first signs are vague and common to so many other conditions. Early cat FIP symptoms include fever, weight loss, decreased appetite, and lethargy.

But after a few days, other signs of FIP start to appear which are more worrying and give the disease the two forms it’s known for: “wet” and “dry” FIP.

Symptoms of ‘Wet’ or Effusive FIP

In wet FIP, fluid builds up in the abdomen making a swollen tummy one of the most obvious signs. This might also happen in the chest cavity causing breathing problems. But other diseases can cause this fluid accumulation as well, so it’s important to wait for more clear diagnostics from your vet in order to make a presumptive diagnosis.

Symptoms of ‘Dry’ or Non-Effusive FIP

In dry FIP in cats there will be minimal fluid accumulation and the symptoms will be vague and not specific to only one illness: weight loss, vomiting, or lethargy. Inflammation might also develop and affect various organs such as eyes, kidneys, lungs, or skin.

In both cases, once the symptoms appear they will progress rapidly in a matter of days or weeks.

How is FIP Diagnosed?

With no disease-specific symptoms or feline FIP test, there is no simple way for vets to diagnose FIP. This is why a series of tests will be used including blood work to identify any abnormalities or x-rays to look for fluid build-up in the body. A biopsy of inflamed tissues has the best chances of revealing FIP in cats, but this requires surgery which is not recommended if a cat is too ill. And even if the biopsy is performed this does not always result in a definite diagnosis.

What is the Treatment for FIP in Cats?

Unfortunately, FIP is a fatal disease in many cases, but there are treatment options that will alleviate some of the symptoms to help make your cat more comfortable. However, research for FIP treatment options continues and there are early signs that medication or even a FIP vaccine that prevents this disease might be possible one day.

Currently the best thing pet owners can do is discuss all the available options (which can include supportive treatments where appropriate) with their vet and be emotionally prepared for the situation in which euthanasia is the most humane step to take.

Can FIP in Cats Be Prevented?

Without a vaccine, there is no known way to prevent the feline coronavirus from triggering the FIP disease. But owners can help prevent this virus getting into their cat’s systems in the first place and reduce the likelihood that once in there it will mutate.

Keeping the litter box far away from the cat’s food bowl and cleaning it more often can help reduce the transmission of the feline coronavirus. And while many stressful situations for our pets can’t be avoided, there are ways to reduce their frequency, such as spacing out events that can be frightening for the pet. So, for example, if you’re moving into a house, make sure you don’t acquire another cat at the same time.

Crowded or poorly maintained cat boarding facilities can also contribute to the spread of the feline coronavirus. So, it’s always a good idea to visit or research any boarding facilities before bringing your cat in. The cattery should be well-managed, cleaned at least twice a day and there should be no bad odors.

And don’t forget to always keep an eye on unusual symptoms in your cat and contact the vet if they persist as soon as possible. Even a cough that won’t go away can be a revealing sign of something else going on in your cat’s body.

If you notice your cat coughing, here is our handy article explaining the top reasons why your cat might be coughing.

Want more cat health tips? Get advice from our experts with our other cat health articles.

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