Cat FIP feline infectious peritonitis symptoms treatment and cure

Cat FIP: feline infectious peritonitis, symptoms, treatment and cure

Feline infectious peritonitis, or FIP, is one of the worst infectious diseases a cat can catch in their lifetime.

This disease is transmitted through contact with other cats but always from cat to cat; it is not transmitted to humans; and there is currently no official cure or vaccine. Contagion to humans is impossible for this disease that affects cats, even though it is caused by a virus that unfortunately we humans also come in contact with: a type of Coronavirus.

The Coronavirus in cats that causes FIP

The problem with this disease is precisely its pathogen, a virus belonging to the Coronavirus group. Since the 2020s, we humans have also unfortunately experienced what it means to deal with a Coronavirus infection, and today we know much more about it. Check out the government website for news about the Coronavirus Pandemic.

Coronaviruses are mutant viruses, that is, viruses that when they replicate in the body can take very different forms.

SARS-CoV-2 is an example, we humans have been affected by it a lot, with very serious consequences, and it has also affected a few domestic animals, tragically as victims. Remember that animals from what we know can be affected by SARS-COV-2, but they do not transmit the infection. Read a clarification here.

FIP is caused by another type of Coronavirus, FCov, a group 1 alphacoronavirus called feline coronavirus.

Infection of the cat by FCov is not automatically a sign that the cat has FIP: some cats show symptoms of the disease while others do not, so FIP exists in either a benign or malignant form. In this article we will try to understand what the symptoms are and how this serious disease in cats can be prevented.

It must necessarily be prevented because, as we have said, it cannot be treated using official drugs here in Italy, and if symptoms occur and any treatment is administered in a timely manner, it always ends in the death of the cat. It is therefore a fatal disease of the cat.

What are the symptoms of FIP in the cat?

The symptoms of FIP can be different depending on how the disease itself takes place.

In the most apparent form, which is immediately recognizable to the owner (also called the wet form), the cat has a particularly swollen abdomen, which as it walks shifts here and there, like a belly full of water.

fip cat symptoms

This is not the case in all cases, however, and we will see why in more detail later, when we discuss infectious cat peritonitis and the progression of the disease.

In other cases, in fact, you may notice yellowish mucous membranes in the cat’s mouth, those of the gums, which are not their normal pink color, or, and this is the most common case, our cat has a fever that does not go away even after the vet has administered antibiotics.

In any case, in cat FIP the symptoms are much more frequent in kittens than in adults, because small cats seem to be much more susceptible to the infection.

So in summary, the symptoms of FIP can be:

  • swollen abdomen
  • yellowish mucous membranes in the mouth, yellowish gums
  • persistent fever

Sometimes the symptoms of FIP can be confused with those of FIV and FelV, so let’s see how to make a correct diagnosis.

Feline peritonitis: cat FIP diagnosis

In infectious peritonitis in the cat, the diagnosis is made at first with a rapid test that can identify, from the stool, the coronavirus infection.

This is particularly useful in identifying FIP-carrying cats, that is, cats in which coronavirus is present, who may have the virus but be well because the virus is in a low pathogenic (benign) form.

The test to make the diagnosis of FIP uses the same principle as the (human) pregnancy test; you put feces on it, instead of urine, and if the virus is present (which in the pregnancy test instead is the ECG) the test reacts and colors blue.

If it turns color, the cat probably has FIP: if it does not turn color, on the other hand, it is still not certain that the cat does not have feline peritonitis, because it may have it at a very early stage.

However, staining is not always indicative of FIP, so you should never euthanize the cat, even if the cat is very sick: you should always wait for confirmation, which will have to be done with laboratory tests such as PCR (which looks at the DNA of the virus) or immunohistochemistry, which looks for the virus directly in the tissues.

In these cases the diagnosis, which in any case is accompanied by clinical symptoms, is practically always confirmed (of course remembering that in the world of medicine we never have absolute certainty).

In any case, no test distinguishes between the malignant and benign forms, neither the simple, outpatient test nor the advanced laboratory tests.

There are guidelines for the diagnosis of FIP in 2022, in which Italy is lagging behind. In August 2022, the EveryCat Health Foundation and the American Association of Feline Practitioners (AAFP) released the 2022 AAFP/EveryCat Feline Infectious Peritonitis Diagnosis Guidelines to the veterinary community. Read them here. In any case, diagnosis is very difficult.

The task force that was responsible for drafting this important guideline document included Vicki Thayer, DVM, DABVP (Feline), co-chair; Susan Gogolski, DVM, DABVP (Canine/Feline), co-chair; Sandra Felten, DVM, DECVIM-CA; Katrin Hartmann, DVM, DECVIM-CA; Melissa Kennedy DVM, Ph.D., DACVIM; and Glenn A Olah DVM, Ph.D., DABVP (Feline).

There are certain signs, according to the widespread guidelines, that may indicate the presence of FIP, which are divided into various categories and various cat apparatuses:

Nonspecific signs

  • Lethargy
  • anorexia
  • weight loss (or failure to gain weight/stunted growth)
  • lack of activity
  • fever (increasing/decreasing; usually <104°F/40°C)
  • jaundice
  • lymphadenopathy
  • pale mucous membranes

Abdominal system

  • abdominal distension
  • fluid wave (ascites)
  • Abdominal masses (e.g., solitary mural intestinal lesions of the colon or ileocecolic junction with regional lymphadenopathy)
  • diarrhea
  • Lymph node enlargement (necrogranulomatous lymphadenitis)

Respiratory system

  • Respiratory dyspnea
  • tachypnea
  • Cardiac system
  • Cardiac tamponade
  • heart failure (pericardial effusion)

Reproductive system

  • scrotal enlargement (effusion)
  • priapism

Neurological system

  • Neurological seizures
  • Abnormal behavior (dementia, aggression, anger, concealment/retreat)
  • Central vestibular signs (nystagmus, head tilt, circles, obtuse appearance, postural reaction deficit),
  • anisocoria
  • ataxia
  • tetra – or paraparesis
  • incoordination
  • hyperesthesia
  • seizures
  • paralysis (brachial, trigeminal, facial or sciatic nerves)
  • cortical blindness

Ocular apparatus

  • anterior ± uveitis
  • posterior or chorioretinit
  • blindness
  • hyphema
  • perivascular cuffing (retinal vasculitis) and fluid accumulation (retinal detachment)
  • hypopyon
  • fibrinous exudate
  • keratic precipitates
  • dyshoria
  • anisocoria
  • iris color change


  • Toxic epidermal necrolysis
  • intradermal papules
  • signs of vasculitis/flebitis
  • skin fragility syndrome

In the PDF document I have linked above there are also numerous indications for accurate tests that may bring us closer to a diagnosis of FIP.

Feline FIP progression

The progression of cat FIP is very, very slow and variable, generally, although it can take a few weeks or a few years from when the cat becomes infected to when the disease manifests itself.

In cat peritonitis, incubation can therefore take a very long time, even though the cat was usually infected when it was small.

The fact that it is an unstable virus, in fact, makes it available either in a benign form, say, that causes no damage, or in a malignant form in which the symptoms of infection occur.

It is not to be ruled out that from the benign form of the virus one can switch to the second, because the “good” virus can continue to replicate and give rise to a bad virus, which begins to manifest symptoms; in any case, the diagnostic test can detect both.

When there is the “bad” form of coronavirus in the cat’s body, antibodies react and bind to the virus, although they cannot destroy it; this results in the creation of special structures, called immune complexes, which can act in two different ways, or both:

If the immune complexes puncture blood vessels we have the wet form, in which the fluid in the blood comes out into the abdomen, which swells;

If the immune complexes become embedded within the organs in tubercles we have the dry form, which can be seen in the following image; it is the one that gives symptoms such as yellowish mucous membranes and fever that does not go down.

If they do a little of both, we have the mixed form. Usually the wet form is the one that gives the cat the biggest and most immediate problems.

Feline peritonitis: how does contagion occur?

The FIP coronavirus is a virus that replicates mainly in the intestinal mucosa, and is then excreted with feces; for a cat to be infected with FIP, therefore, it is necessary for it to come in contact with the feces of infected cats, or otherwise with objects that have come in contact with feces of infected cats, such as bowls and litter boxes; by sniffing or licking, the cat can pick up the virus, which is very resistant in the environment.

Another possible route of transmission of FIP is transplacental transmission, which means that a sick pregnant cat passes the coronavirus directly to kittens, which in this case are already born infected; as with cats that become infected with feces, symptoms of the disease can be variable.

In infectious cat peritonitis, contagion to humans is impossible, because like many viruses this one is also strictly cat-specific. Dogs do not get it either, as they have their own specific coronavirus that affects only dogs.

Therefore, one can live with a cat sick with FIP even for many years and always be safe from infection, because we cannot catch the cat coronavirus, just as the cat cannot catch our flu or our chickenpox. It can instead, in rare cases, catch our SARS-COV-1, thus our COVID.

Treatment and therapy: can you recover from FIP?

The bad news is that cat FIP has no official cure in Italy, but there are “unofficial” cures if you put a lot of effort and money into it. And if you are not timely, the cat is doomed. This is the state of affairs.

Of course, something can be done to make the cat’s life as good as possible, with drugs (usually anti-inflammatory) to help reduce the symptoms of the disease, but the virus is there, and there is no medicine that can destroy it.

The survival of an FIP-positive cat is highly variable: if a cat develops, or catches, the more malignant forms, the course is always negative, and the cat may die within a few weeks, and there is nothing that can be done.

If the cat gets the benign form, on the other hand, it may even have the life expectancy of a healthy cat, unless it happens that at some point in its life the virus becomes malignant.

The vaccine for cat peritonitis, FIP, on the other hand, does not exist: or rather, it exists but is not protective (it is used only in catteries and colonies, but it stops there) because the virus is so variable that, in any case, even if a vaccinated cat caught the virus it could catch a different form that would not be recognized by its body.

In fact, the vaccine is of no use against infectious peritonitis in the cat. We humans have also seen the variability of coronavirus and the need to develop new effective vaccines for its variants. We have been fortunate that in many cases mostly for humans the vaccines work and have helped contain the pandemic.

Because it is a very serious and often incurable disease, you will come across several drugs on the Internet that are not approved in Italy but are abroad. FNovi (Federazione Nazionale Ordine Veterinari Italiani (National Federation of Italian Veterinary Orders) has issued a statement regarding the sale through the internet of drugs such as GS-441524 and Mutian X : read the statement

In 2022, researchers at the University of California, Davis, School of Veterinary Medicine have initiated new clinical trials focused on improving treatments for feline infectious peritonitis, or FIP, and are currently “enrolling” patients at the UC Davis Veterinary Hospital.

Several clinical trials are underway, to alleviate the symptoms of this disease with antiviral drugs, stem cells, GS-441524 and even some drugs designed and created to counter Covid-19 infection in humans. Research during the Covid pandemic among humans has been greatly accelerated, and we hope this will benefit cats as well. Read the news here.

Research on this disease must move forward and the drugs tested must be made available in Italy as soon as possible so that we can say that FIP can be cured. Also because the virus mutates very quickly and we need to move forward with research also in order to have rapid tests that can diagnose the disease, as it was for us humans with Covid rapid tests, which at least allowed us to contain contagions.

One important figure who has devoted so much of his life to finding a cure for FIP is Dr. Niels Pedersen, who in August 2022 gave a presentation at the feline health symposium “Health Breakthroughs for Every Cat: FIP and Beyond” at the University of Florida-Gainesville to an audience of both in-person and virtual attendees from 20 countries around the world.

Since 1964, Dr. Pedersen has been studying and publishing research on FIP, and in 2019 he was able to announce that FIP was reclassified from fatal to treatable. Here he is in a photo (thanks to Zen by Cat) with Smokey, one of the very first cats cured of FIP with the experimental drug GS-441524.

Dr. Niels Pedersen

To learn more about Dr. Pedersen and his research on FIP, check out his official website.

More information on research and treatment for cat FIP is the Zen By Cat site, who with their FIP Warrior Club do great outreach and are supportive to a lot of people who have FIP-positive cats.

Their site also talks about the FIP vaccine, as well as treatment with the GS-441524 drug. We remind again that these are drugs that are not approved in Italy. However, the vaccine has low efficacy, and is not effective at all in cats already exposed to coronavirus.

Treatment with the drug GS-441524 is based on Dr. Pedersen’s research, should be done for a minimum of 12 weeks or 84 days with daily administration by injections or oral medication. The treatment should be followed by blood tests after 12 weeks.

Again according to the Zen by Cat website, each injectable vial costs from $65 to $120 depending on the brand and concentration of the drug, and the daily dose is determined by the cat’s weight and the type of FIP the cat has. The result is a very expensive treatment indeed, there is even a simulator of the total costs and from a quick look I saw that it ranges from $2,500 to as high as $25,000 for the entire 12-week treatment.


The fact that it is a disease with no approved official treatment options makes prevention more important than ever for a cat.

The biggest risk factor is certainly the possibility of meeting other cats, who may themselves have the coronavirus and thus FIP.

If a cat does not encounter other cats it will definitely be healthy, whereas if it has caught the virus by now, by the time we notice it is always too late.

Cleaning the litter box, limiting the cat’s outings, and neutering it so that it goes out less are good ways to protect it, whereas the time when we have to be most careful for transmissions is when we want to get another cat having already one: in this case before taking the decision we do a Coronavirus test (a FIP test does not exist) to both of them ( us or whoever sells/gives it to us) to avoid that if one of them is sick, the other one could be infected.

What I hope is that research will move forward, even with the new knowledge gained from research on the coronavirus that affected us humans. The studies that have already been done on feline coronavirus have been helpful in developing vaccines and treatments for our Covid, hopefully the research on this will be helpful in finally saving so many cats from FIP.

What about you, have you ever lived with an FIP or Coronavirus positive cat? Tell us your experience in the comments.

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