FIP is no longer a death sentence thanks to COVID-19

By Olivia Baker, BVSc, Otaki Vets

Feline infectious Peritonitis (FIP) is a viral disease of cats that has until recently been considered a fatal disease.

Feline infectious Peritonitis (FIP) is a viral disease of cats that has until recently been considered a fatal disease. It is a complex disease to diagnose and therefore can easily be missed early on when symptoms are subtle. FIP is a coronavirus, and as most of us are now aware, so is COVID-19, so a lot of the antivirals that were developed to treat COVID-19 in people are now helping us with the treatment of FIP in cats. I hope that this article will make you more aware of these earlier possible symptoms so you can seek veterinary advice early to give a better chance of saving your cat.

What is FIP?

FIP is a disease that is caused by an infection with Feline Coronavirus. Coronaviruses are a common group of viruses that often infect the upper respiratory tract (nose and throat) or gastrointestinal tract (intestines). Coronavirus infection is extremely common in cats, especially where large numbers of cats are kept together. The virus is commonly detected in the faeces of many cats. In most cats, infection causes no signs or just mild diarrhoea that resolves without treatment.

However, occasionally the virus mutates inside a cat, and if their immune system reacts in a certain way, they could develop the disease we know as FIP. It is important to be aware that detecting feline coronavirus in your cat does not mean they have FIP! You cannot tell between the coronavirus causing FIP and the one that’s just causing a bit of diarrhoea.

How would my cat get FIP?

Coronavirus is spread through faecal oral contamination, and there is more chance of this in environments where there are more cats living together. The majority of cats contract coronavirus early in life. The experts are not really sure what makes a cat with coronavirus go on to have FIP disease. They suspect that there is some stressful event in the cat’s life that triggers the virus to mutate into the disease state. So just because you cat is positive for coronavirus, doesn’t mean that they’re guaranteed to develop FIP.

How serious is this disease?

Previously FIP was almost always fatal. It is a very serious disease and if we cannot treat them early enough there is still a high chance we might lose them. Even with new treatments available we may not be able to save them.

What should I look out for?

Often the only sign you will see is a high temperature and due to this fever, your cat will lethargic and dull. Just not really their erratic flat out full of energy self. It is important to note that this high temperature can wax and wane, so it may not consistently be high. They often don’t want to eat either and therefore lose weight. Where the virus attacks first and how your cat’s immune system deals with it, will heavily influence what signs you’ll see.

If your kitten is wobbly, stumbles, their eyes flicker a bit or they seem to walk in circles, these could all be signs of the neurological form of FIP, especially if it is coupled with a high temperature.

If your kitten has a sore eye that doesn’t seem to be healing with eye ointment, has a high temperature that is not coming down even when you’re treating with meloxicam (a non-steroidal anti-inflammatory drug that can reduce temperatures), this could be an ocular form of FIP.

If your kitten has a belly that just keeps getting bigger, and you’ve wormed them and it feels like there is a bunch of fluid in there – this could be the effusive (fluid in their abdomen) form of FIP.

If your kitten is struggling to breathe, they have been given a flea treatment that covers for lungworm, the vet has ruled out cat flu, their heart sounds ok – this could be the effusive form of FIP and the fluid is accumulating on their chest.

Who is more likely to get it?

There are no absolutes with FIP, any cat can get it! However, purebreds are at higher risk of getting FIP. It is also seen more commonly in cats less than 2 years of age; however, I have seen a case in a four-year-old cat. Male cats, especially entire male cats are more likely to contract it over females. Cats from multi-cat households are more at risk too, however, we do see it in single cat households, as the kitten would have contracted the coronavirus at an early age when it was with their siblings and then it has mutated later to FIP. We also find FIP runs in families, so if one of your other cats has had FIP in the past, there’s a higher chance your currently sick cat could have it.

What should I do if I suspect my cat might have FIP?

Take your cat to the vet as soon as possible. The sooner you get a diagnosis and start treatment the better the chances of saving your cat.

How will the vet diagnose my cat?

This is where things get really tricky, as there is no specific test for FIP and testing to see if they have coronavirus in their system is not going to help us. We need to consider a bunch of factors to try and reach a diagnosis and these are some of the ways that vets will try and reach a diagnosis:

  • Is the cat showing signs that are consistent with FIP
  • Are they in the higher risk category?(e.g. purebred, younger cat, colony cat, male entire etc.)

Are there some typical changes in routine blood tests? Such as:

  • Low numbers of white blood cells (WBC)
  • Increase numbers of neutrophils (a type of WBC)
  • Anaemia (low numbers of red blood cells)
  • Increased globulins (one of the major proteins in the blood)
  • Increased bilirubin (jaundice – yellowing of gums and eyes can be seen with this)
    – It is important to understand that these blood work changes are not specific to FIP and if they don’t have the above changes, it does not rule out FIP. Especially in the early stages of FIP the virus might not have caused enough damage to cause these blood changes.
  • Is there fluid in the cats abdomen or chest?
    – We might take x-rays or do an ultrasound scan to try and confirm this if it isn’t obvious.
    – We can then test this fluid. If the fluid is high in proteins, it is suggestive of FIP and the fluid can be sent to the lab to test for presence of Coronavirus via a PCR test.
  • Is the cat showing neurological signs?
    – MRI scan can show vasculitis in the brain, which is consist with FIP.
    – Evaluate the cerebral spinal fluid – take a sample of the fluid from around the spine and send to the lab for analysis.
  • Does the cat have a sore eye? – You can take a sample of the fluid around the eye and have it tested.
  • If the vet has detected lesions in organs or lymph nodes needle samples can be taken.
  • Tissue samples can be taken at surgery or post-mortem to confirm diagnosis.


Time is of the essence though and if the vet has a strong suspicion that your cat has FIP they may start a treatment trial to see if your cat improves. Early on in the disease where your kitten only has a high temperature, is lethargic and not a lot else, if an antiviral is given and their temperature goes down and they are much brighter this in itself can be diagnostic.

The above tests are extensive, costly and time-consuming. In an ideal world and best practice we would do all the above tests so we could be completely sure before starting treatment, however if your vet has a strong suspicion of FIP, I think it is reasonable to start treatment while waiting for some of these tests to come back.

If your kitten is showing neurological signs, and has a high temperature and falls into the high-risk category, the only real way to reach a diagnosis of FIP is to do an MRI. An MRI is much more expensive than the cost of the treatment trial, so if clients cannot afford to do both, I feel it makes sense to start medication and if they improve, we’ve got a presumptive diagnosis.

What can we treat FIP with?

There are no registered treatments for FIP in New Zealand, unlike Australia and UK. This means in New Zealand if you treat with one of the following antivirals you are treating “off label”, i.e. at your own risk. Although these drugs are not registered for cat, your vet can access antivirals from compounding pharmacies such as Optimus. The cost of treatment is not as expensive as it once was, and we now have three options available to us. Remdesivir (an injection), GS-441524 tablets and Molnupiravir tablets. Remdesivir and GS-441524 have been trialled a lot more than Molnupiravir and are the two drugs that are registered overseas. There is a current research study being performed at ARC Veterinary Specialists in Auckland, so if you do find your cat does have FIP and you choose to treat it is a good idea to become part of that study. This study will go a long way towards getting these antivirals registered in New Zealand. Your vet will know how to get you signed up with this study.

Molnupiravir has not been studied quite as extensively as the other two antivirals but is proving to have some great results also. It was initially cheaper than GS-441524 and Remdesivir, which makes it more attractive, but it is a twice daily tablet, so the costs may work out similar. It is therefore worth considering both treatments and seeing what will work best for you and your cat. Pilling a cat once daily for 84 days may be worth the extra cost versus twice daily.

Right so I’m treating my cat with an antiviral, is that them saved now?

If only it was that easy! Unfortunately, there are no guarantees, even if you started treating your cat early. This is something to consider when making the decision to treat, the cost of the antivirals are not cheap and there is no guarantee they will be curative. Your cat may also relapse, and you’ll need to treat again.

Some of the things that can go wrong with treatment are:

  • Not consistently getting the medication into the cat
  • Not giving high enough dose
  • Not treating for long enough (needs to be treated for 84 days – the life span of the macrophage cell the virus lives in)
  • Not changing the size of the tablet as the cat grows.


Can I prevent my cat from getting FIP?

Not really is the short answer, as Feline Coronavirus is ubiquitous among cats. You can do some things to try and minimise their chances of getting it, such as not housing your cats in groups bigger than four cats. Try to minimise stressful events as much as you can in young cats. Keep litter boxes away from food and water bowls and clean/disinfect them regularly (daily).

I’ve heard of Wet FIP and Dry FIP, why haven’t you mentioned that?

Historically FIP was grouped into Wet FIP (cats that present with big bellies full of fluid) and Dry FIP (where the cats didn’t have the big belly). This definition can still be helpful when deciding what dose of drugs to give a cat with FIP but is largely redundant now. Research has now shown that cats can get a continuum of symptoms and they all depend on where the virus is attacking first and how the body reacts to it. Cats with FIP that are untreated will all end up as a ‘wet FIP’ even if they started as a ‘dry FIP’, because the virus causes a vasculitis (leaky blood vessels) and so fluid will start to accumulate everywhere as the disease process gets worse.