Feline Infectious Peritonitis (FIP)

Feline infectious peritonitis (FIP) is caused by a virus something called a 'feline coronavirus'. This virus is very common in cats but it rarely causes disease. Most of the time your cat with a coronavirus will have no obvious signs apart from just mild diarrhoea. Some cats may also show mild symptoms of problems with their upper respiratory tract - things such as sneezing, watery eyes, and nasal discharge (rather like a cold in humans).

Vets describe the strains of coronavirus which cause mild symptoms or no serious problems as the feline enteric coronaviruses (FECV). However, in some cases mutations of the virus (spontaneous changes to viral proteins) will cause a severe disease predominantly affecting the intestines, kidney and brain. This virulent strain of coronavirus is often referred to as feline infectious peritonitis virus (FIPV). This can take one of two forms: wet FIP, which results in the accumulation of large amount of fluid in the abdomen and (less often) in the chest, and dry FIP which is characterised by widespread scarring of the cat's intestines.

The science of FIP

Coronaviruses primarily infect the upper respiratory and gastrointestinal tract of mammals and birds. In technical terms these viruses are described as enveloped viruses with a positive-sense single-stranded RNA genome. The genomic size of coronaviruses is extraordinarily large for an RNA virus. Inorganically, coronaviruses are divided into five groups. Feline coronavirus as well as canine coronavirus (CCoV) and transmissible gastroenteritis virus (TGEV) belong to group I. Cats seem to be susceptible to all group I coronaviruses. Some feline strains are thought to originate from recombinations of FCoV and other group I viruses, such as CCoV. What this means is that though you are extremely unlikely to catch a cold from your cat, your cat can catch a cornoavirus off you, and is even more likely to catch it from a dog.

Feline infectious peritonitis was first described as early as 1963, and even today it is not fully understood how this disease develops and spreads. It is known that the coronavirus is transported throughout the body by infected white blood cells. The response of the immune cells to the virus-infected cells is what causes the pathology. The body reacts violently to the invasion, and a strong inflammatory response occurs around blood vessels in the tissues where these infected cells are located -and often the body's response is well out of proportion to the amount of virus present.

Today it is generally accepted that feline coronavirus (FCoV) and FIP-inducing viruses (FIPV) represent virulent variants of the same virus rather than septe species of virus. Although many tests exist for identifying a coronavirus - including tests which detect the anti-virual antibodies in the plasma (ELISA) and tests which detect viral genetic material in tissue or body fluid (using polymorphonuclear chain reaction -PCR) - none of these tests can distinguish between FCoV and FIPV. And so far, FCoV and FIPV have remained serologically and genetically indistinguishable.

What are the symptoms of FIP

It is believed that FIP is the single most important infectious cause of death in young cats. Some ten percent of kittens which get infected die during their first year. In cats that develop FIP, the symptoms can appear suddenly. The early symptoms are quite general: loss of appetite, weight loss, depression, a rough coat, and fever. Once the cat becomes symptomatic, the disease increases in severity over the course of several weeks, often ending in the cat's death.

As mentioned above, there are two major forms of FIP, an effusive, or 'wet' form, and a noneffusive, or 'dry' form. In general, cats with non-effusive FIP will start to develop symptoms more slowly than those with the effusive form. In the late stages of the dry FIP, there is chronic weight loss, depression, anaemia, and a persistent fever that does not respond to antibiotic therapy.

The most dramatic symptom of the effusive form of FIP is an accumulation of fluid in the abdomen and, less commonly, in the chest. Early in the disease, the cat may show similar symptoms as a cat with the dry form, including weight loss, fever, loss of appetite, and lethargy. The wet form of the disease often progresses rapidly, and the cat may quickly appear pot-bellied due to fluid accumulating in the abdomen. sometimes so much fluid can build up that it may become difficult for the cat to breathe normally.

FIP can be difficult to diagnose because each cat can have different symptoms that are similar symptoms of many other diseases.

How is FIP spread?

FIP is relatively uncommon in the adult cat population. It is also not very contagious, because by the time the cat develops the full-blown disease it is no longer very infectious, though the Feline coronavirus exists in large quantities in the saliva and feces of cats with acute infection. To a lesser extent this also occurs in recovered or carrier cats (cats with the virus but no symptoms), so it can be transmitted through cat-to-cat contact and exposure to feces. The virus can also live in the environment for several weeks. The most common transmission of feline coronavirus occurs when infected female cats pass along the virus to their kittens, usually when the kittens are between five and eight weeks old. Also in multi-cat households, the cats can infect each other through contaminated feces, when sharing litter common trays.

How can I protect my cat from FIP?

FIP is more common in multi-cat households and the biggest risk of cross-infection is among cats which use the same litter tray. So good hygiene is very important in preventing the disease.


Unfortunately at present, there is no cure or effective treatment for FIP. Some treatments may induce short-term remissions in a small percentage of cats, but generally speaking FIP is a fatal disease. Treatment is generally aimed at supportive care, such as good nursing care and nutrition, and alleviating the inflammatory response of the disease. Cats with FIP are often treated with corticosteroids, cytotoxic drugs, and antibiotics. Supportive care may also include fluid therapy, draining accumulated fluids, and blood transfusions. Resent studies using INF-alfa (which is an anti-viral agent) have shown promising results but it is still too early to say how successful this drug will be in treating FIP.


There is only one licensed FIP vaccine available in the United States. It is based on an attenuated (weakened) live virus. Studies so far have shown that the vaccine very little effect in preventing FIP, and it is not generally recommended by the American Association of Feline Practitioners Feline Vaccine Advisory Panel. Primucell FIP, produced by Pfizer Animal Health, is a temperature-sensitive, modified-live virus vaccine that is given as an intranasal vaccine, and is licensed for use in cats at least 16 weeks of age. The vaccine appears to be safe, but the risks and benefits of vaccination should be weighed carefully. Cat owners should consult their vet to help decide if their cat should be vaccinated.

Note: This information is for guidance only. It is not intended to replace consultation with a licensed practitioner.

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