Feline Infectious Peritonitis Update

Feline Infectious Peritonitis, FIP, is a disease of cats causing a

Sally, our totally indoor cat, contracted FIP through contact with a stray cat through our back porch screen.
Sally, our totally indoor cat, contracted FIP through contact with a stray cat through our back porch screen.

variety of illnesses.

For new information on FIP, including treatment, click here.

FIP is caused by a coronavirus, so-called because under an electron microscope it looks like a crown or “corona.” In its original form, enteric coronavirus, it has only the ability to cause a mild, self-limiting diarrhea. Virus is “shed” from the intestinal tract for months, and other kittens can be infected orally when sharing litter boxes, food and water bowls, and through mutual grooming. Adult cats are usually more resistant to infection by coronavirus, with the peak period for transmission being around 9-10 weeks of age.

Coronaviruses, however, have a strong tendency to mutate. Mutation causes a change in the virus, just as it does with influenza viruses in people. Mutation is the reason we require new flu vaccines periodically.

When feline coronavirus mutates, it can gain the ability to cause Feline Infectious Peritonitis in cats.

As the body reacts to the organism, granulomas develop.


In the wet form of FIP, fluid accumulates in the abdomen (and sometimes the chest cavity, also). Fluid collection can be so dramatic that affected cats become pot-bellied. If fluid builds up in the chest it can compress the lungs to the extent that breathing becomes difficult. Also, granulomas can invade lung tissue, resulting in further compromise of air exchange.

The dry form is similar, but without fluid gathering in the cavities. Cats can switch between the two forms during the course of the disease. These patients may also suffer eye problems, brain and spinal cord lesions. Seizures, loss of alertness and ataxia (wobbliness) may result.


Cats typically present as “poor do-ers.” They experience weight loss, decrease in appetite, poor hair coat and termination of self-grooming. Vomiting may occur if the intestinal tract is obstructed by granulomas. The physical examination is usually unrewarding, simply revealing the obvious.

Furthermore, routine laboratory tests are not much help. The chemistry profile may reveal abnormalities if granulomas have invaded the liver and/or kidneys, but such damage is not diagnostic of FIP. The CBC, complete blood count, may show an elevation of white blood cells in response to the inflammatory process. Even so, that is a finding associated with hundreds of syndromes in addition to FIP.  Anemia, a reduction in red blood cell count, is also a common finding.

For many years “the test” for FIP wasn’t much help, either, mainly because it wasn’t a test for FIP. Until recently it was nearly impossible to tell apart the body’s response to one coronavirus or another. Therefore, all we could say with a “positive” test was that your kitty had been exposed to and had responded to some coronavirus. Only in recent years have we had a test that was specific, and now your pet’s doctor can draw a sample of fluid, if present, from the chest or abdomen send it to a laboratory and usually know whether FIP is causing your cat’s illness.

An even better laboratory test is performed on affected white blood cells (immunocytochemistry) or organ samples (immunohistochemistry). This very sophisticated test is available in specific laboratories. Failure of these tests occurs if too few affected cells are submitted, or tissue is obtained from an unaffected organ.


Unfortunately, even with an accurate diagnosis we still have no effective treatment for Feline Infectious Peritonitis and the percentage of cats succumbing to the disease is in the high 90s. Symptomatic therapy can help make your kitty more comfortable, but nothing eliminates the infection and nothing totally stops the immune system’s self-destructive path. Even so, the course of the disease is often slow and cats may survive for many years. Corticosteroid treatment limits the body’s self-destructive immune system attack. Polyprenyl Immunostimulant may also hold promise.

Longevity tends to be better in patients with the dry form.


FIP is difficult to transmit until kidney cells or intestinal cells are damaged (unlike transmission of pre-mutation coronaviruses). Once on a fomite (litterbox, water or food bowl, countertop) the virus may persist for weeks. Young cats/kittens are more easily infected than adult cats. Therefore, additions to an FIP-infected household should observe a two-month waiting period and/or be limited to adult cats.

Those who are breeding cats must be constantly aware of the role of genetics in the development of FIP. If FIP develops in two litters, properly isolated and cared for, from a given queen or tom, that individual should be removed from the breeding program.

A vaccine is available against FIP, but its use is controversial. Many experts believe that administration of the vaccine worsens the body’s response when/if natural disease exposure occurs. On the other hand, some practitioners trust it to reduce the incidence of the disease in multi-cat households and catteries.

Dr. Randolph


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