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FIP stands for
Feline Infectious Peritonitis which means inflammation of the lining
inside the belly (peritoneum) due to infection in cats. This
terrible condition can actually affect just about anywhere in the
body but the main locations it occurs in are inside the chest,
inside the belly or the brain. Because it is now known that it
can affect multiple locations, we tend to use the abbreviation to
describe it rather than its full name.
Simply stated, FIP is an almost always fatal disease that mostly
affects young cats. It is a complicated disease and the processes
encompass infection, genetics and immune responses.
The underlying cause is a virus called coronavirus. Most
cats (as many as 90% in catteries) are infected with the enteric
(intestinal) form of coronavirus. This can cause diarrhoea but is
not necessarily severe or long lasting. After infection, the
virus can live in the lining of the intestines for years and cause
no overt damage but stress (eg bringing another cat to the
household, moving house or being ill with something else) can lead
to replication of the virus. In a few cats who have a
genetic susceptibility, when the virus replicates, there will
be mutations to the FIP form of coronavirus. The
main distinguishing feature is that this form can continue
to replicate inside a particular sort of white
blood cell called a macrophage. Macrophages are meant to
‘gobble up’ infections so the virus persisting here sets up for an
The disease formed depends on the degree of immune response and
the organs where inflammation occurs. The typical signs are a
persistently elevated body temperature and fluid accumulation
within the belly but FIP is not a typical disease so the
possible clinical signs are many and varied.
Examples include (but are not limited to): fits (seizures), cloudy
eyes (or other eye changes), fluid accumulation in the chest,
jaundice and non-specific signs like poor growth, lethargy or
being off food. Individual cats vary in the signs they show.
Some cats can show mild signs for months before more severe
When we suspect FIP, our investigations are actually trying prove
another, hopefully more treatable, disease. We usually start with
blood and urine testing and typical changes include,
anaemia, elevated globulins (inflammatory proteins) and elevated
bilirubin (associated with jaundice) but these don’t always
occur and are not specific for FIP. There are blood
tests that can show exposure to coronavirus (serology) but they
are not specific for FIP and most cats with coronavirus never get
FIP; this test can actually be negative in later stages of FIP.
Because of the difficulty in interpreting results, we don’t
normally run serology tests for this disease.
The only conclusive tests are those that show large numbers
of coronavirus in places they shouldn’t be. This is done by
‘tagging’ the coronavirus in a fluid or biopsy sample. The
technique used to assess a suspicious fluid sample is called
ImmunoFluorescence Antibody (IFA) testing. A positive
results definitely confirms FIP but sometimes cats with FIP can be
negative (ie a false negative). The technique used to assess a
biopsy sample this way is called immunohistochemistry and
is this is a conclusive test.
There is no definitive treatment for FIP. The sad truth is
that most cats with FIP die. A recent journal article has
suggested a treatment that appears to have been successful in 4
out of 12 cats. There are some problems with the paper (that the
authors acknowledge) so the suggested treatment is not proven.
One of the medications for this is very expensive which is a
further barrier to trying it in every FIP cat.
We have attempted this treatment with several patients in the past, and have
been unsuccessful in all but one case. You can read about our very lucky patient, Stanley, and his recovery
Please feel free to discuss any aspects of this. It is a
difficult disease to understand and we are really sorry that your
cat was unlucky enough to have it.
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