What causes the symptoms associated with Feline Infectious Peritonitis?

Feline Infectious Peritonitis (FIP) is caused by a virus, specifically a mutated form of the feline coronavirus (FCoV). In the majority of cats, feline coronavirus is a common and usually harmless infection, but in some cases, it mutates to cause FIP, which leads to severe immune-mediated disease. The symptoms associated with FIP, such as fever, weight loss, and abdominal swelling, occur as a result of the body’s immune response to the virus. When the virus infects immune cells, it can cause a cascade of inflammatory responses that lead to fluid accumulation and damage in various organs, which is characteristic of the disease.

In contrast, a bacterial infection would involve the invasion of bacteria, which is not the case for FIP, as it is viral in nature. A parasitic infestation involves different pathogens, such as worms or protozoa, which also do not pertain to FIP's etiology. An autoimmune response refers to the body’s immune system mistakenly attacking its own tissues, which is not the primary mechanism of FIP. This highlights why a viral cause is central in understanding the symptoms related to Feline Infectious Peritonitis.