FIP- Feline Infectious Peritonitis

Generally when we have to write about this frustrating and deadly virus it is somber and with memories of patients lost. Instead today I write to you about advances in the treatment of this disease and the possibility of remission. While these treatments are still in both the early stages of understanding and research they have created possibilities we never had before. (Above Image: Henry is a British Shorthair who is now in remission from his FIP.)

We dedicate this post to all the cats who have been lost to FIP. We have all known and been heartbroken at the outcome for so many cats.

KIngston is a Siberian who sadly lost his battle with FIP.

What is FIP?

FIP is short for Feline Infectious Peritonitis. It is caused by a mutation of the Feline Coronavirus or FeCoV. It belongs to the same family of viruses as the one creating havoc to the world today, but it is not able to be spread from cats to you and I. FeCoV is common among cats, generally picked up in early kitten hood and causing a usually self-limiting diarrhoea (no coughs or chest infections for them.) Many cats will carry anti-bodies to this virus in their blood for the rest of their lives, without any complications or disease. In some cats, the virus manages to hide way in the immune system, dormant and inactive, well managed by the immune system of the individual. For reasons we still don’t understand, in some cats the virus mutates and becomes active again. Due to the mutation, the virus is able to escape the body’s immune system and begins to cause FIP. This is estimated to occur in 1-5% of cats who were infected with FeCoV earlier in their lives.

While cats can present with similar symptoms, the mutation is individual for each cat. Therefore it is not contagious to other cats. This unfortunately makes diagnosis harder, because the tests we have for the original virus that causes diarrhoea are not reliable once the mutation has occurred. Recall that the virus also hides inside the immune systems cells, called macrophages, making it much harder to catch in the act. It is no wonder that this virus has eluded us so well for the last 70 years. In fact, these new treatments we will discuss today have only been researched since 2016. One of the positive things about human COVID-19 is that it prompted production and availability new drugs for this family of viruses. We in the veterinary field are now able to utilise some of them for this terrible disease.

Here you can see Pako’s Fluid file abdomen, caused by his FIP.

What Does FIP Look Like?

Not every cat will have all the symptoms or present in the same way. This is another part of the struggle to diagnose FIP with confidence. Traditionally we discuss two forms of FIP; the wet form and the dry form. It does over-simplify the possible symptoms, but can help sometimes group symptoms together into likely appearances. FIP can affect any cat of any age, but it seems to be over-represented in young, male cats. Both pedigree and non-pedigree cats can be affected, and it has been documented all over the world.

The easiest to both see from the outside as well as suspect FIP in the wet form. Named for the abdominal effusion that causes a large distended belly, the wet form is caused by vasculitis or inflammation of the blood vessels. In the viruses‘ fight with the immune system, the blood vessels of the body become inflamed and irritated, making them leaky. While the leaks are small and the actual red blood cells cannot escape, the fluid making up the blood can. Often this leaked fluid then collects in the abdomen (belly) as an abdominal effusion or in the thorax (chest) as pleural effusion. Collecting fluid in the chest will result in much worse symptoms and will be noticed much sooner, as it effects breathing and the sometimes heart function. Fluid collected in the abdomen takes time to cause difficulties as there is a lot more extra space in this area of the body.

Blue is a British Shorthair now in remission from his FIP.

Cats will often be off their food, lethargic and sometimes have a waxing and waning fever. If the fluid has collected in the chest, then shortness of breath, weakness and distress may be evident. Abdominal effusion may only cause the distention of the belly initially, but often the pressure of the fluid will result in reduced appetite and decreased activity. Often these cats are also anaemic (having a low red cell count) and will have changes on their blood work to support the overactive production of globulins by the immune system. No one of these symptoms or results is enough to diagnose FIP. Multiple findings and tests are used to increase our suspicion and rule out other possible causes of the fluid effusion.

Dry FIP is the termed used to describe cases without fluid build up. Many dry FIP cats will have lethargy, fever, anaemia or other symptoms depending on what part of the body is most affected. Some may have large lymph nodes or even small masses in the abdomen, others may have changes to their eyes (uveitis most commonly) or neurological symptoms. FIP in these cases is caused by that same type of over-reaction of the immune system but doesn’t result in fluid to be lost from the vessels. Similar blood testing results are seen in these cases, but further supportive evidence is still needed to diagnose FIP such as special staining on tissue biopsies.

Milo is a Domestic Medium hair now in remission from his FIP.

Testing For FIP

While no single test is enough to diagnose FIP, the gold standard is finding the virus itself inside the white blood cells from a part of the body that is affected. In cases with effusion, the fluid can be tested to try and find the virus in action, hiding in the macrophages. This fluid should also be tested and analysed to ensure no other causes or complicating factors are present. Cases without effusion are much harder to get samples from, but often biopsy of masses or lymph nodes can be tested fo the active virus. Again, this should always be combined with other testing to help rule out other causes. Please note, finding FeCoV in faeces is not useful in cases with FIP. Carriers may shed non-active virus in their stool and be positive on faecal testing. Blood testing for FeCoV only assess for anti-bodies which may be present at high levels even in older cats without FIP. If you are concerned with results your cat has received please make an appointment with one of our vets to discuss these and have your cat assessed.

New Treatments

Since 2016 promising research had shown there are compounds which can stop this virus and put cats into remission. The short version of the story is that none of the companies producing these back then saw a big enough market to make money and decided not to make it available commercially. Many cats from the originally study are still in remission today (5 years later.) What did become available from unreliable sources overseas were black-market versions of drugs similar to those studied. While we as veterinarians can not condone their use, we did see cats treated with these products and with some success. Fortunately in 2019 due to the human COVID-19 outbreak, production and research into a drug called remdesivir began. It showed great promise in human COVID and was subsequently made available to the veterinary industry in Australia late last year.

Pako is a British Shorthair who is now very happily in remission now from his FIP.

Belonging to the same groups of drugs studied in 2016, remdesivir has now been used in several cases with success. Not 100% success unfortunately, but as we previously discussed there are some cases where a full diagnosis of FIP has not been easy and this drug has still been tried due to suspicion of disease. It is unclear if those cases that do most respond are due to misdiagnosis or drug resistance. Remdesivir is given as a series of injections under the skin and aids the body’s immune system in debilitating and stopping the reproduction of the mutated FeCoV. While this medication is not yet licensed for treatment of FIP we have started to treat cats and had success in Australia.

More research is currently being undertaken to help us understand this medication and treatment of FIP. Our team at the Perth Cat Hospital is currently working with the researchers at Sydney University on this research and are recruiting cats to participate in a study on FIP and possible treatments. If you would like your cat to be checked or discuss this further with our team please contact our reception team to book an appointment.