peritonitis (FIP) is a fatal, incurable disease that affects
cats. It is caused by
Feline Infectious Peritonitis Virus (FIPV), which is a mutation of Feline
Enteric Coronavirus (FECV/FeCoV). Experts do not always agree on the specifics of
FIP. However, the most common theory is that the normally benign FECV mutates
into FIPV. The mutated virus has the ability to invade and grow in certain white
blood cells. The immune system's response causes an intense inflammatory
reaction in the containing tissues.
Transmission and infection
FECV is very common, especially in places where large groups of cats are kept
shelters, catteries, etc). Cats become infected by inhaling or ingesting the
virus. The most commonly cited transmission source is feces, although
virus-contaminated surfaces such as food dishes and clothing can trasmit the
virus as well.
Despite the prevalence of FECV, most infected cats do not develop FIP. Often
exposure to FECV produces no symptoms, but may cause a mild upper respiratory
disease. Therefore, a cat with no symptoms whatsoever might still be an FECV
carrier and pass the virus to another cat. Even if FECV does not mutate in the
carrier, the newly infected cat might still contract FIP.
FIP effusive fluid
There are two main forms of FIP: effusive (wet) and non-effusive (dry). While
both types are fatal, the effusive form is more common (60-70% of all cases are
wet) and progresses more rapidly than the non-effusive form.
The hallmark symptom of effusive is the accumulation of fluid within the
abdomen or chest, which can cause breathing difficulties. Other symptoms include
lack of appetite, fever, weight loss,
Dry FIP will also present with lack of appetite, fever, jaundice, diarrhea,
and weight loss, but there will not be an accumulation of fluid. Typically,
though, a cat with dry FIP will show ocular or neurological
Cytology of FIP-induced fluid showing neutrophils, macrophages and lymphocytes
The symptoms associated with FIP are often non-specific, which can cause
diagnosis to be very difficult. A definitive diagnosis requires examination of
affected tissues for the FIP virus. This is usually performed post-mortem, but
can be performed via tissue biopsy. Histopath examination of tissue samples is
usually the cheapest and most readily available diagnostic, however a PCR test is also
available for use with fluid or certain tissue samples that is considered
More commonly, a presumptive diagnosis is made based on clinical signs and
evaluation of abdominal or chest fluid, if available. Fluid caused by FIP tends
to be yellow in color and have elevated protein levels. Blood tests can also be
performed to bolster a presumptive diagnosis by looking for coronavirus
antibodies and elevated protein. Coronavirus titers are not
considered diagnostic in and of themselves due to the ubiquity of FeCoV, but may
be used in conjunction with clinical symptoms to make an FIP diagnosis.
As there is no cure for FIP, treatment is symptomatic and palliative.
Typically the owner is advised to make the cat as comfortable as possible until
it becomes clear that the cat is suffering. Prednisone
or other immunosuppressive drugs prescribed by a veterinarian may help to
prolong the cat's life for a few weeks or months, but may be contraindicated in
certain cases due to concomitant infection(s). Effusive FIP usually progresses
too rapidly for any meaningful therapy to be attempted.
Quarantine may be advised if there are other cats in the environment, however
because the details of transmission aren't well understood desired measures of
quarantine will vary among practitioners.