Todayโs path rounds is on ๐๐๐ฅ๐ข๐ง๐ ๐ข๐ง๐๐๐๐ญ๐ข๐จ๐ฎ๐ฌ ๐ฉ๐๐ซ๐ข๐ญ๐จ๐ง๐ข๐ญ๐ข๐ฌ (FIP)! This was a suggestion 
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
FIP is a viral infection of cats that is characterized by ๐ฏ๐๐ฌ๐๐ฎ๐ฅ๐ข๐ญ๐ข๐ฌ (leaky vessels) and inflammation. It has two forms, ๐๐๐๐ฎ๐ฌ๐ข๐ฏ๐/๐ฐ๐๐ญ, where excess fluid accumulates in the body cavities, and ๐ง๐จ๐ง-๐๐๐๐ฎ๐ฌ๐ข๐ฏ๐/๐๐ซ๐ฒ, where the inflammation forms distinct nodules.
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
This is a disease unique to cats! Typically young, intact male cats get this condition.
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐
๐๐?
FIP is caused by a ๐๐จ๐ซ๐จ๐ง๐๐ฏ๐ข๐ซ๐ฎ๐ฌ (but not *that* coronavirus), and follows a somewhat interesting path of development. Feline coronavirus is extremely common in cats. Cats acquire the virus through ingestion of food contaminated with feces from infected cats. From there, it invades into the intestinal cells and sets up shop, producing more virus and releasing it into the feces. Up to 90% of cats with feline coronavirus have no ill effects or clinical signs from the disease, and carry on their mischievous lives quite happily.
However, in about 5% of cats, the virus undergoes a mutation that allows it to leave the intestinal cells and enter ๐ฆ๐๐๐ซ๐จ๐ฉ๐ก๐๐ ๐๐ฌ (the immune systemโs major clean-up cell) and replicate there. Because macrophages are found in all body tissues, this allows the virus to spread widely throughout the cat.
So why is this particularly interesting? Because of the life cycle of coronavirus, this means that the mutated coronavirus that causes FIP is not actually infectious to other cats, because it canโt be shed in the feces. Neat!
๐๐ก๐๐ญ ๐๐๐๐ข๐๐๐ฌ ๐ฐ๐ก๐๐ญ๐ก๐๐ซ ๐ ๐๐๐ญ ๐ ๐๐ญ๐ฌ ๐ฐ๐๐ญ ๐จ๐ซ ๐๐ซ๐ฒ ๐
๐๐?
FIP is very responsive to the immune response the body produces against it! If the immune system is operating at full capacity, then the cat likely will resist the virus and not develop any clinical signs. If the immune system has a significant deficiency, the virus will continue to run rampant throughout the body and cause the more severe form of FIP, wet form. The dry form falls somewhere in between those two outcomes, with a partial immune response leaving only a few infected cells that develop into nodules.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
As mentioned above, FIPโs primary problems are vasculitis and inflammation. In the wet form, the leaky vessels cause fluid to build up in the body cavities like the abdomen, chest and in the pericardial sac around the heart. This fluid typically has ๐๐ข๐๐ซ๐ข๐ง in it, a component of the blood that helps form clots. When it is loose in a body cavity, it interacts with the surfaces of organs and forms long strands attached to surfaces and floating free in the fluid. Gross. The fibrin strands and fluid can prevent organs from working properly, most notably the lungs. Lungs do not like to expand when surrounded by fluid!
In the dry form, inflammation is the primary problem, causing formation of inflammatory nodules within and on the surface of organs. These nodules take up space in the organ causing reduced organ function, and if they enter the brain, can even cause neurologic signs and blindness!
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
The clinical signs are highly variable, because it depends on which organs or body areas are affected. However, fever and weight loss are fairly common non-specific findings. Veterinarians may use ultrasound to try and identify free fluid in the body cavities in the wet form, or to try and find the nodules of the dry form. The veterinarian can also run bloodwork to look for abnormalities or even take a sample of the free fluid to help diagnose the disease.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
Unfortunately, FIP has no definitive treatment, and has a very poor prognosis. One study showed that the median survival time after diagnosis was just 9 days! Most treatments attempt to control the inflammation and vasculitis, however they are often not very effective. Currently, there are several antiviral treatments that are being tested, with some reasonable results!
๐๐ก๐จ๐ญ๐จ๐ฌ
1) The abdomen of a cat with wet form FIP, showing abdominal fluid and stringy strands of fibrin.
2-3) FIP nodules over the intestines.
4) FIP nodules on the kidney.
5) Remember how fibrin forms long stringy strands? Here are fibrin strands running between the lungs and the ribcageโฆ nasty!
6) Some extremely sad lungs covered with fibrin strands and sitting in fluid in wet form FIP.
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 2. Sixth Edition.
Levy, J.K. Overview of Feline Infectious Peritonitis. Merck Veterinary Manual 2014.
Photos 2-4 courtesy of Noahโs Arkive.
Photos 1, 5 and 6 courtesy of University of Calgary Diagnostic Services Unit.
