FIP – Feline Infectious Peritonitis. If you mention this term to someone who works with cats, you’ll see a person with a hopeless look on their face shaking their head sadly.


FIP is a disease seen in young cats and kittens. They seem okay, then suddenly they are not okay. Then they die. It’s hard to diagnose definitively, meaning there is no simple, noninvasive test we can do that will tell us for sure.


And, until now, there has been no hope for a cure. Once they get sick, they die.


The first time I encountered FIP in real life (meaning after veterinary college), it was a young cat belonging to a family who had the means to consent to any testing I was able to do. This kitten was sick, his abdomen was swollen, and he had stopped eating.


Blood testing showed some changes, but nothing that was a definite cause. Looking at the fluid from his belly gave some information, but these folks wanted to be sure about a cause. Xrays showed fluid in the abdomen and ruled out heart failure, but still didn’t tell us what was the cause. I actually ended up going to exploratory surgery with that little fellow, and by then the evidence inside his abdomen (peritonitis) was pretty stark. We didn’t wake him up, poor little fellow.


I still remember the helplessness I shared with that family on that late summer evening many years ago. There were so many things we could do, but nothing we did was enough. We couldn’t beat that terrible virus.


But now, researchers are giving us hope. Maybe we can stop this nasty virus, maybe we can start saving some of these little souls.


This is a strange disease, and the more we know about it the more complex the picture becomes.


FIP is caused by a virus. But, 90% of cats with this virus (feline coronavirus) never get sick. That means testing for exposure to the virus (antibodies) or even for the virus itself doesn’t mean the cat has the disease.


Researchers believe the disease comes about when the virus mutates and starts to multiply inside the cat’s own immune system cells. These cells can travel anywhere in the body. The virus eventually kills the cells. But also, the immune system starts attacking its own infected cells.


This causes inflammation in different parts of the body all at the same time. We see fever, sometimes flu-like symptoms, and then signs of inflammation in different organs. Often, fluid begins to build up inside the abdomen.


By looking at blood tests and testing the abdominal fluid, we can see parts of the picture and rule out other causes. The only way to be sure it’s FIP is to test tissues inside the abdomen by taking biopsies, but these kitties are often too sick to survive surgery. FIP is a fatal disease.


When we look at the new antiviral research and see that ‘only’ seven out of twenty cats (35%) achieved and maintained remission from the disease, it doesn’t look that optimistic. But, compared to the reality of 100% death, that 35% chance looks pretty good for a start.