FIP usually appears in one of two forms: Effusive (wet) and
Non-Effusive (dry). It should not be thought, however, that there are
two different FIP diseases. The results of the infection are a
continuum on a scale, with the ‘wet version’ being one end, the ‘dry
version’ being in the middle, and a ‘carrier’ being the other end (a
carrier is where the cat has successfully fought off the disease but
may still be able to expose other cats to the virus). The way this
happens is when a cat is exposed to FIPV, if its immune system gives a
poor response, the wet form will develop. If it gives a better
response, the dry form will develop. In the best responses, the cat
will not develop either form of FIP, although it may be a carrier of
the FIP virus.


The wet form is more common, and more rapid in progression than the dry
form. It is characterized by the abdomen and/or chest progressively but
painlessly distending with fluid. If this occurs in the chest,
respiratory distress can occur due to compression of the lungs and
release of fluid into the airways. The lining of the affected cavity
will be covered with white, fibrin-containing areas (fibrin is a
protein that is the center of a blood clot), often on the liver and
spleen. Certain types of lymph nodes may be enlarged. Other signs
include jaundice; mild anemia; and gastrointestinal, ocular (e.g. eye
ulcers or severe conjunctivitis), and neurological signs may also occur.


The dry form is more rare (but appears to be becoming more common), and
more slow in progression, often making diagnosis difficult. There is
minimal fluid build-up, although weight loss, depression, anemia, and
fever are almost always present. Signs of kidney failure, liver
failure, pancreatic disease, neurologic disease or ocular disease may
be seen in various combinations. Often the organs in question
develop a characteristic pyogranulomatous inflammation (this is a chronic
inflammation resulting in a thickening of the tissue and local
accumulation of white blood cells). Unfortunately biopsy of these lesions
is the only definitive way to diagnose this form of FIP and is usually
done in the form of a post-mortem diagnosis.