Feline Infectious Peritonitis (FIP)


What is Feline Infectious Peritonitis (FIP)?

Feline infectious peritonitis (FIP) is a viral disease that can occur in wild and domestic cats. It is caused by a type of virus called a coronavirus. There are many different strains of feline coronavirus, which differ in their ability to cause FIP.  Most feline coronavirus infections are relatively harmless, but this initial harmless infection may later mutate to cause FIP in some cats. To further complicate things, cats with a strong immune system infected with a more harmful strain of feline coronavirus may be carriers of the virus. Meaning they may shed the virus without ever showing signs of disease.  Also, the virus can remain dormant in the body for months to years before infected cats eventually develop full-blown disease. This makes FIP a very confusing disease that is hard to understand.


Fortunately, FIP is an uncommon disease. Unfortunately, FIP is a progressive and usually fatal disease. Transmission of FIP is most common in places where large groups of cats are housed together indoors. The virus is shed in feces and cats become infected by ingesting or inhaling the virus, usually by sharing cat litter boxes. Transmission of the virus directly from cat to cat is possible, but is less common.

What are symptoms of FIP?

Clinical FIP generally has a gradual onset over several days, weeks or even months. Clinical signs can be non-specific; fever, decreased appetite, weight loss, and an unkempt appearance.

FIP existis in two forms: wet or dry. The difference being to what extend of fluid accumulation there is in the cat’s body.

The wet form is more common and is characterized by fluid accumulation in the abdomen and/or the thorax. This will lead to swelling of the abdomen and breathing difficulties, as the body fills up with fluid.

The dry form causes inflammation in various body systems. This can lead to weight loss, anorexia, fever and lethargy. Depending on which organ systems are involved, other signs may include jaundice, vomiting and diarrhea and dehydration.

How is it diagnosed?

A test that detects antibody to feline coronavirus is available, however this test can not differentiate between the harmless and harmful strains of the virus. A positive or high titre does not necessarily mean the cat has developed  FIP, it could also mean that the cat was exposed to feline coronavirus and has eliminated the virus or is a carrier for it. Similarly, a negative titre usually means that cat has not been exposed to feline coronavirus and is unlikely to have FIP, however it could also mean that the FIP disease is in an early stage and not detectable or that the cat is infected with FIP, but is no longer making antibodies.


Since antibody testing can only help with diagnosis, other laboratory diagnostic testing is usually recommended. Cats with FIP will show a high antibody titre along with a low lymphocyte count and elevated blood globulin levels. In suspected cases of wet FIP, the fluid in the lungs or abdomen can be sent for testing. In cats with FIP, the fluid will have globulin levels higher than 32%, and albumin levels less than 48%. These test results along with history and clinical signs are important for diagnosing this disease.

The only definitive testing for FIP is to biopsy affected tissues and have them examined by a veterinary pathologist. Unfortunately, this is only done after the cat has died to confirm that FIP was the cause of death.

How is FIP treated and prevented?

There is no cure for FIP,  a cat surviving FIP is very rare. Since treatment is not available, supportive care is offered to make the cat more comfortable. Supportive care will involve fluid therapy, good nutrition, antibiotics for secondary bacterial infections, administration of a steroid medication and periodic draining of the abdomen or thorax if the cat is suffering from the wet from.

Good hygiene is important in densely populated cat populations and multi-cat households to prevent the spread of FIP. Frequent scooping and complete cleaning of litter boxes is the most important. Followed by keeping all bedding, dishes and toys clean to decrease the chance of transmission. Very young or old cats or those with a compromised immune system should be kept separate from “healthy” cats to lower the risk of transmission by a un-diagnosed carrier cat.

There is a vaccine to prevent FIP in cats, but is it not recommended. There is limited evidence to show it is even effective to prevent FIP.