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Feline Infectious Peritonitis (FIP)

What is FIP?

Feline infectious peritonitis (FIP) is an infection of cats caused by a virulent strain of feline coronavirus (FCoV). In FIP this virus can replicate throughout the body causing a wide variety of clinical signs. Unfortunately, in virtually every case, once clinical signs of disease develop, the cat will go on to die from FIP, or will need to be euthanased due to progression of the disease.

What are the clinical signs of FIP?

The clinical signs of FIP are extremely diverse. Broadly two forms of disease are recognised, so called 'wet FIP' and 'dry FIP'. In wet FIP the most obvious signs are due to accumulation of fluid in body cavities - usually either the abdomen (eventually causing marked swelling and distension of the abdomen) or the chest (around the lungs) causing difficulty breathing. In cases of dry FIP, the disease mainly manifests as areas of inflammation within various tissues of the body. This can lead to very diverse and often complex clinical signs including neurological disease, ocular disease, liver disease, kidney disease and intestinal disease. Some cats also have a mixture of the 'wet' and 'dry' forms of the disease. Affected cats are often quite ill, becoming lethargic with a poor appetite and weight loss and there is often fluctuating pyrexia.

The course of the disease can vary from a few days to a few months. In the early stages, some cats remain quite bright, but over time there is an inevitable deterioration. Unfortunately, none of the clinical signs with FIP are diagnostic for this condition - many other diseases can cause similar signs.

How can FIP be diagnosed?

The diagnosis of FIP is very difficult. The development of typical clinical signs may lead to a suspicion of the disease, but these alone are not diagnostic. On routine blood tests, FIP will commonly cause a variety of changes, including changes in haematology (red and white blood cell counts) and biochemistry (blood proteins, tests of liver and kidney function etc.). However, again although these changes may suggest or support a diagnosis of FIP, they cannot confirm a diagnosis as the changes seen are not confined to cases of FIP. Where fluid develops in the chest or abdomen, retrieving a sample of this fluid is a simple procedure and analysis of this fluid is very valuable. In cases of FIP the fluid has a very high protein and globulin (one type of protein) concentration. The finding of a fluid typical of FIP is strongly supportive of a diagnosis, although again there are some other diseases that can cause accumulation of fluid with similar characteristics.

At present, the only way to confirm a diagnosis of FIP is to look at histological (microscopic) changes in affected tissues (obtained by biopsy or at post-mortem examination). Where there is significant doubt about a diagnosis, or where it is important to be sure whether FIP is present or not, examination of tissues in this way is essential.

What is coronavirus serology (the 'FIP test')?

Coronavirus serology is a laboratory test that detects antibodies in a cat,s blood sample against feline coronavirus (FCoV). However, this blood test does not have the ability to distinguish between different strains of FCoV, and cannot differentiate between strains that cause FIP and those more common strains that do not. Additionally, the presence of antibodies does not necessarily imply that the cat is currently infected with FCoV, although in practice it appears that in most antibody positive cats FCoV can be found. Although this blood test is often used as part of the investigation of a suspected case of FIP, it is not particularly helpful as a very large number of perfectly healthy cats have positive test results reflecting the high level of exposure to FCoV in the cat population (most strains being unlikely to cause any significant disease).

In a healthy cat, the finding of antibodies against FCoV in a blood test is neither surprising nor alarming. This is common (as is the finding of antibodies against numerous infectious agents) and no special precautions are needed unless the test is being performed as part of a programme to try to eliminate or control FCoV infection in a cattery situation.

How is FIP spread?

The virus that causes FIP is in fact a variant (spontaneous mutation) of a very common infection in cats. Infection with feline coronavirus (FCoV) is extremely common (probably between π and Π of all pet cats have been infected with this virus at some point), but in the vast majority of cases the virus will cause nothing more severe than transient diarrhoea. However, occasionally a variant of the virus emerges that is much more pathogenic and in this situation, unless the infected cat can control the infection with a good immune response, FIP will develop.

How common is FIP?

Feline infectious peritonitis is a relatively uncommon disease in cats, but is more common in colony cats and in young cats (less than 1-2 years old). Accurate figures are difficult to obtain, but it is estimated that the incidence of FIP in general household cats is in the order of 0.02% (ie, around 1 death per year in every 5000 cats). However, where many cats are kept together in close confinement (where the virus can be readily transmitted) and where there are young cats present (which are more susceptible to developing FIP) the disease is much more prevalent. Thus in some multicat households or catteries, the incidence of FIP may be as high as 5%.

Can FIP be treated?

Unfortunately there is no known treatment for FIP. In cats where the disease is diagnosed or suspected the immediate action depends on the severity of the disease. In some cases immediate euthanasia is necessary on humane grounds. In others, palliative treatment may be provided with anti-inflammatories (eg, prednisolone) for a period of time to make the cat comfortable. However, the disease will eventually progress and euthanasia will inevitably be required.

Can my cat catch FIP at a cat show?

In most cases, the virus that causes FIP arises as a spontaneous mutation of an existing FCoV infection in a cat, and the FIP-producing virus is not generally spread from cat to cat. The risk of directly 'catching' FIP at a cat show is thus extremely low. However, FCoV infections could potentially be spread at cat shows. The virus is usually shed in the faeces, and may contaminate the haircoat. Thus if hygiene precautions are inadequate there is potential for the virus to be spread between cats. Adequate disinfection (tables, hands etc.) and minimising the amount of handling will help to reduce this risk.

What should I do if I suspect my cat has FIP?

The most important action to take if you suspect your cat has FIP is to seek veterinary advice as soon as possible. A variety of investigations may need to be done to investigate the possibility of FIP (clinical examination, blood tests, radiographs etc.). Where a definitive diagnosis is needed then a tissue biopsy will probably be required.

In most cases, cats that develop FIP will not be shedding the virulent FIP-causing virus and therefore will not be a risk to other in-contact cats. However, this will not invariably be the case and, as a precaution, where possible, it is probably best to try to keep a suspected clinical case separate from other cats.

How can FIP be controlled in pet cats?

Control of FIP is difficult, but as it is a relatively rare disease in the general pet cat population, specific control measures are generally not warranted. No effective vaccine is available in the UK, and although one is available in some other countries, it is not entirely reliable and the disease is not common enough to generally warrant vaccination of pet cats.

If FIP is suspected in a pet cat, it should be isolated from other cats and appropriately investigated (see above). If disease is confirmed and there are other cats in the household, it is possible for the disease to be spread, but in general most adult cats are able to resist infection and are unlikely to go down with disease. If there are young cats, and especially kittens, in the household, these are at greater risk and should be monitored closely for signs of disease. Blood tests on a healthy cat are of no value in predicting whether it will develop disease. Good hygiene should be maintained. The virus is spread mainly by the faecal-oral route and it is quite fragile, not surviving long in the environment. The virus is susceptible to most commonly used disinfectants that are safe for cats (

What should I do if my cat dies from FIP, and when can I get another?

As most cats that develop FIP do not shed virulent FIP-causing virus, the risk to any other cats is very low. However, some additional precautions may be taken to further reduce any potential risk:

  • If there are no other cats in the household, waiting 6-8 weeks before obtaining another cat will help ensure there is no or minimal risk from environmental contamination with the virus. Disinfecting food and water bowls, litter trays and areas where the cat has been will also help as the virus is susceptible to all commonly used disinfectants (see

  • If there are other cats in the household, although they will probably all have been exposed to and infected with FCoV, there is only a small risk they will have been infected with, or developed, an FIP-causing strain of the virus, and again only a very small risk that they could pass this on to other cats. To minimise such risks further it is possible to:

    - Avoid bringing any new cats, and especially kittens, into the household for the following 6 months

    - Serotest any remaining cats every few months to follow their antibody status, and wait until they become antibody negative before introducing any other cats. The basis for this is that antibody negative cats are generally thought to be free of virus, and therefore new cats introduced would not be at risk of being infected with FCoV. However, some cats may remain persistently infected with FCoV and if there are several cats it may be necessary to separate them to prevent re-infection between them. If remaining cats are monitored until seronegative, any new additions should also be tested, and be seronegative, prior to introduction. Although feasible, this approach is rarely practical, especially given the low risk of further cases of clinical disease

What should a breeder do who sells a kitten that subsequently dies of FIP?

This is not an uncommon scenario. While it is impossible to know in an individual case how and where the kitten developed the infection, in most cases it will have been infected with FCoV before being sold, and subsequently a mutation in the virus will have allowed the development of the FIP-causing strain.

It is important in this situation that wherever possible the diagnosis of FIP is confirmed and good communication between all parties involved (owner, breeder and veterinary surgeon) is very important to avoid misunderstanding. If FIP is confirmed it should be recognised that this may be a 'one-off' case or a very intermittent problem. However, it is likely that the breeding household does have endemic FCoV infection and this is dealt with under the section 'What should be done in breeding households with endemic FIP?'

What should be done in breeding households with endemic (recurrent) FIP?

Realistically it is extremely difficult and time consuming to eradicate FCoV infection from breeding catteries with an FIP problem, although it can be done. It requires regular testing of cats to segregate cats exposed to (and potentially infected with) FCoV from the other cats, and eventually probably rehoming some cats that are healthy but persistently infected with the virus from the colony. Even if this is achieved, maintaining a FCoV-free colony is challenging.

It is important to have cases of suspected FIP confirmed - other diseases can mimic the appearance of FIP.

More realistically, several measures can be advised to reduce the spread of FCoV and reduce the risk of FIP occurring (which is mainly a problem in the kittens and juvenile cats):

  • Having at least one litterbox for every two cats, located in easy to clean areas, away from food and water bowls to prevent cross-contamination
  • Faeces should be removed from litterboxes at least once daily, and litter should be completely changed as often as possible (at least weekly, and ideally daily) and the trays disinfected
  • Cats should be kept in small stable groups, ideally of four or less to minimise spread and maintenance of the virus in a household
  • Unless there are specially built and designed facilities, ordinary households where cats are bred should house a maximum of 8-10 cats and kittens. Higher numbers of cats increase the risk of FCoV infection.
  • Avoid breeding from any queens which repeatedly produce litters that develop FIP

If there are repeated cases of FIP, or if a breeder wishes to produce kittens where the risk of FIP is the lowest possible, there are means of attempting to breed kittens that are free from exposure to the virus. Pregnant queens can be isolated one to two weeks pre-partum, and the queen is subsequently kept isolated with her kittens (whilst employing good hygiene procedures to prevent environmental spread of infection to the kittens). Following weaning (which can be performed early - at 5-6 weeks of age - if necessary), the queen can be removed and the kittens still kept isolated and tested at 12-16 weeks of age for FCoV antibodies. If the litter is seronegative, the isolation procedure will have been successful and they can be re-homed as FCoV negative kittens. Although potentially successful, this requires considerable commitment from breeders, and there are some concerns about the behavioural development of kittens when they are reared in isolation up to the age of four months.

What should be done in rescue catteries to control FIP?

There is no justification for routine serotesting of cats in a rescue centre, and euthanasia should never be performed simply on the basis of a high antibody titre. However, because of the relatively large numbers and turnover of cats in a rescue shelter, this is a situation where there is a higher than normal risk of FCoV infection being spread and of FIP developing. Several recommendations can be made to reduce this risk:

  • Wherever possible house cats individually and not in groups

  • If individual housing is limited, as a priority keep this for

    - Cats that require quarantine (sick cats or new arrivals)

    - Cats that are pregnant

    - Kittens and juveniles (who are at a higher risk of FIP and other infectious diseases)

  • If some cats have to be group-housed, keep them in small groups (ideally less than 4-6 individuals per group) and do not mix cats >from different groups.

  • Use sneeze barriers and good cleaning/disinfection regimes to minimise the risk of spread of FCoV and other infectious diseases

  • Use a separate litterbox for each pen that is only used in that pen and is regularly disinfected (ideally daily).

  • Allow at least one litter tray for every two cats if they are in groups

  • If cases of suspect FIP develop

    - Where possible have the diagnosis confirmed (by tissue histopathology), as many other diseases can look like FIP.

    - Do not immediately rehome any cats that were in direct contact with the affected individual. These cats are the ones most at risk, and ideally should be kept for 2-3 months before rehoming (the longer they remain healthy, the lower the probability that they will develop FIP).

    - If good hygiene is being maintained and if cats are not allowed to mix then the risk to any other cats is extremely small

What should be done in boarding catteries to control FIP?

The risk of FIP in a boarding cattery should be very low assuming that good standards are maintained. Guidelines on cattery design and maintenance are available in the FAB Boarding Cattery Standard and the FAB Boarding Cattery Manual (see: Spread of any infectious disease, including FCoV can be prevented if there are appropriate hygiene measures (individual litter trays, adequate disinfection), sneeze barriers, and no direct contact between cats.

Can cats carry the SARS (severe acute respiratory syndrome) virus?

Although the SARS virus that affects humans is a type of coronavirus, there is absolutely no evidence that this virus can be transmitted between humans and domestic cats. There is some evidence that Civet cats may be involved in the spread of this disease to humans, but these are not actually cats at all (not members of the Felidae family).

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