FIP is a complex condition and difficult to diagnose because coronaviruses are very common in cats, usually causing no disease at all or only a mild short-lived diarrhoea.  Occasionally, though, the virus mutates (changes) inside a cat, and if their immune system reacts in a certain way, they can develop FIP.  Unfortunately, our tests that find viruses do not distinguish between a coronavirus causing FIP and one causing no signs at all.

Confirming a diagnosis is difficult and involves putting together the puzzle of clinical signs, imaging findings (xrays, ultrasound and/or MRI), blood, fluid and needle-aspirate results, as well as virus-detection tests such as PCR.

FIP can cause many different clinical signs, depending on the parts of the body affected and how the immune system reacts.  Clinical signs, especially in the early stages, can be vague, with a fluctuating fever, lethargy and a reduced appetite.  Other signs may develop after days, weeks or even months.  These signs depend on the organ affected, but may include fluid in the chest or abdominal cavity, neurological signs such as an unsteady gait or seizures, bleeding in the eyes or signs associated with disease in the liver, kidney or other internal organs.

In Blackie's case, he was just a little "off-colour" for a short period, then 2 months later, developed a bloated tummy.

Vet, Bryn, performed blood tests, an abdominal ultrasound, tests on the abdominal fluid and a coronovirus PCR, and a diagnosis of FIP was made.