FIP is a disease caused by Feline Coronavirus. Feline Coronavirus infection is very common and normally causes a mild intestinal disease, which may either be asymptomatic or cause transient diarrhoea.
In some individuals FECV may mutate to a form that is able to infect certain white blood cells (macrophages and monocytes). This form of the virus is called Feline Infectious Peritonitis Virus (FIPV). The virus then spreads throughout different organs within these white blood cells. Normally, the body mounts an immune response to eliminate viral infections. Some cats are able to fight this mutated form before signs become apparent. In other cats the immune system is unable to kill the virus, in fact it is this inflammatory reaction that actually creates damage to the body's tissues and causes the signs seen with FIP.
How do cats get FIP?
Cats don't usually catch the mutated form of the virus directly. FECV is the form that is transmitted between animals. This is usually via saliva or faeces of an infected cat, either through grooming or contact with contaminated objects such as feeding bowls, litter trays or bedding. Once FECV infection has become established, mutated forms (FIPV) may arise during viral replication.
It has been shown that cats that live in close proximity with each other (for example in catteries or multi-cat households) are much more likely to be exposed to FECV. This means that they are also more likely to go on to develop FIP because there is simply more virus replicating in their systems. It has also been found that certain genetic lines of cats are more susceptible to developing FIP. Typically young cats (between the age of 6-months to 2-years) tend to get FIP, however cats of any age can contract the disease.
What are the signs of FIP?
FIP exists in two clinical forms. The more common 'wet' form is charaterised by fluid accumulation in the abdomen and/or the chest, and a 'dry' form that is caused by inflammation in various body systems. In reality, many cats have a combination of the two forms. The clinical disease may progress rapidly over a few days (particularly the wet form) or may wax and wane for many weeks to months.
The wet form typically causes swelling of the belly and/or breathing difficulties, as the respective body cavities fill with fluid. The dry form is typically more insidious, with weight loss, anorexia, fever and depression commonly present. Depending on which organ systems are involved, other signs may include jaundice, vomiting and diarrhoea, dehydration, excessive urination and drinking, neurological signs or inflammation within the eyes. The occurrence of these secondary signs is highly variable and may mimic many other disease
How is FIP diagnosed?
The diagnosis of wet form FIP is often fairly straightforward because of the classic yellow sticky fluid that accumulates. As previously mentioned, the dry form can mimic many other diseases and is often a diagnostic challenge. Normal blood tests may show changes that are suggestive of FIP, for example, increased protein in the blood, or changes to white cell counts, however these may also be seen with many other inflammatory diseases. The detection of coronavirus antibodies in the blood of a cat will only indicate if the cat has been in contact with the virus and does not differentiate between FECV and FIPV. A new test is being developed at the University of Sydney, which allows pathologists to see the virus within white blood cells in the body's tissue. This is considered to be the only accurate test for FIP, however this does require the collection of biopsy samples.
How is FIP treated?
Although many treatments for FIP have been tried, none have been shown to be conclusively effective and the disease remains an ultimately fatal condition.
How can I stop my cat getting FIP?
Unfortunately it is very difficult to prevent a kitten from becoming exposed to FECV within a cattery environment. It is impractical to expect that an animal will never be exposed to coronavirus, however it is important to try to select overtly healthy animals that come from a hygienic environment that is not overcrowded. Selecting a cattery that has no history of FIP in its lines is best, however this may not be easy to determine given that there is often a stigma associated with such diseases. There is no effective vaccine available that will prevent FIP. If a cat in your household has been diagnosed with FIP it is unlikely to directly pass this on to other family cats, however they may have been exposed to FECV or be susceptible individuals in their own right. Ultimately, it is impossible to determine which individuals will develop FIP.