Peritonitis (FIP) affects cats and is lethal. Some believe it is the cause of Feline Infectious Peritonitis Virus (FIPV) which is a mutated form of Feline Enteric Coronavirus. The most common theory is that the normally benign FECV mutates into FIPV. This virus has the ability to invade and replicate in certain white blood cells. Due to immune response there is an inflammatory reaction in the tissues. Although fatal it is rare, it occurs roughly in one of every 5000 households. A nasally administered vaccine is available.

In places where large groups of cats are FECV is common. Infection is spread through inhaling or ingestion of the virus. Feces are the most common transmission source although food dishes and clothing can also transmit the virus.

Exposure to FECV often does not produce any clinical signs other than mild diarrhea. This means a cat with no signs can still be a carrier. In any carrier the virus can mutate into FIP causing form. Immune compromised, young, and old cats are at a higher risk of that.

FIP has two main forms: effusive and non-effusive. Both types are fatal but most cases are effusive and progress much quicker than the non-effusive form. Accumulation of fluid within the abdomen and chest is the hallmark sign of effusive FIP. Other symptoms include lack of appetite, fever, weight loss, jaundice, and diarrhea. Non-effusive FIP will have similar symptoms but without the accumulated fluid. The infected cat will normally show ocular and/or neurological signs. The cat might develop difficulty in standing up or walking, becoming functionally paralyzed over time. Since the signs aren’t specific to FIP it can be hard to diagnose. Diagnosis usually comes through clinical suspicion, physical examination findings, presence of abdominal fluid with characteristic chemistry changes and examination findings. Fluid caused by FIP tends to be yellow in color and elevated protein levels. With these chest fluids a Rivalta test is used to differentiate between FIP and other diseases. The cheapest diagnostic test is a histopathological examination of tissue samples.

Most believe there is no cure for FIP and treatment is symptomatic and palliative only. Prednisone may prolong a cat’s life for a few weeks or months. Since it is not truly infectious disease quarantine is not necessary.