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What is feline infectious peritonitis (FIP)?Feline infectious peritonitis (FIP) is a disease caused by a coronavirus infection. Many different strains of coronavirus are capable of infecting cats, but most do not produce serious disease. FIP-producing strains are distinguished by their ability to invade and grow in certain white blood cells. The infected cells transport the virus throughout the cat's body. An intense inflammatory reaction occurs in the tissues where these virus-infected cells locate. It is this interaction between the body's own immune system and the virus that is responsible for the disease.
Infected cats shed coronavirus in their saliva and feces. Most cats become infected by inhaling or ingesting the virus, either by direct contact with an infected cat, or by contact with virus-contaminated surfaces like clothing, bedding, feeding bowls, or toys. Although the virus can survive for a number of weeks in the environment, it is rapidly inactivated by most household detergents and disinfectants. An inexpensive and effective disinfectant is one part of household bleach in thirty-two parts of water (4 ounces of bleach per gallon of water).
FIP and feline leukemia are caused by different viruses. Some cats that have FIP may also be infected by the feline leukemia virus, but the diseases are two separate entities.
Initial exposure to the FIP virus usually results in no obvious clinical disease, although some cats may experience a mild upper respiratory disease that is characterized by sneezing, watery eyes, and watery nasal discharge. Some cats may experience a mild intestinal disease. Most cats that undergo the primary infection completely recover, although some of them may become virus carriers. Only a small percentage of exposed cats develop the lethal disease: weeks, months, or perhaps years after primary infection.
This disease has two major manifestations. The first is called the "dry form". In the dry form the white blood cells are involved, and cause an inflammatory reaction to the internal organs. These organs do not function normally because of this inflammation, and eventually will fail as the disease progresses
The other manifestation of this disease is called the "wet form", and is where the original name of "peritonitis" (inflammation of the lining of the abdominal cavity) came from. It is called this because fluid accumulates in the abdomen or the chest. The fluid that appears in the wet form is straw colored to yellow in appearance, and has a relatively high protein content. The fluid originates from small blood vessels that have been affected by the immune systems response to the virus. This immune response damages these blood vessels, causing them to leak fluid into the abdominal cavity usually, or thoracic cavity less often.
The virus can also infect the brain or spinal cord. This form of the disease can sometimes be diagnosed by an eye exam. Changes can be noted in the back of the eye, especially the retina. (video)
The onset of clinical signs of lethal FIP may be sudden (especially in kittens), or the signs may gradually increase in severity over a period of weeks. Many cats have nonspecific signs such as intermittent inappetence, depression, rough hair coat, weight loss, and fever. The major forms of lethal FIP are effusive (wet) FIP, noneffusive (dry) FIP, and combinations of both. The most characteristic sign of effusive FIP is the accumulation of fluid within the abdomen and/or chest. When fluid accumulation becomes excessive, it may become difficult for the cat to breathe normally.
Cats that have FIP will have physical exam findings similar to other feline diseases. In the wet form the fluild buildup in the abdomen becomes apparent as time goes on. One of the ways we check for fluid during an exam is to look for a fluid wave. (video)
The fluid that builds up in the wet form of FIP is called ascites when it occurs in the abdomen, and pleural effusion when it occurs in the thorax. The fluid is sticky and usually light yellow to golden color, with a relatively large amount of protein. This is what the fluid looks like just after is has been removed from the body.
This is an x-ray of a normal cats thorax. This cat is laying on its right side, the head is towards the left. You can see the heart and the black lung tissue in the shape of a triangle. The diaphragm (arrows) is the vertical line that separates the thorax on the left from from the abdomen on the right. The liver resides in the abdomen.
This cat has a significant amount of fluid in the thorax (pleural effusion), making it difficult to identify normal organs. You cannot see the heart or diaphragm, and the lung tissue is greatly reduced because of all the fluid. The lungs are unable to expand fully causing significant difficulty in breathing. This pet is very ill and has minimal breathing reserve. It needs immediate removal of the fluid.
After some of the fluid was removed it is possible to visualize more of the organs. There is more lung tissue present and the top of the diaphragm is now visible.
The onset of noneffusive FIP is usually slower. Fluid accumulation is minimal, although weight loss, depression, anemia, and fever are almost always present. Signs of kidney failure (increased water consumption and urination), liver failure (jaundice), pancreatic disease (vomiting, diarrhea, diabetes), neurologic disease (loss of balance, behavioral changes, paralysis, seizures), enteritis (vomiting, diarrhea), or eye disease (inflammation, blindness) may be seen in various combinations. FIP is often a difficult disease to diagnose because each cat can display different signs that are similar to those of many other diseases.
Young cats (less than two years of age), older cats (over ten years old), cats in poor physical condition, and cats undergoing concurrent infections or stress are more susceptible to FIP. It is a relatively uncommon disease in the general cat population, probably affecting fewer than one percent of the cats brought to a veterinarian's office for treatment. In multiple-cat populations such as some shelters and catteries the disease rate can be much higher, affecting up to 10 to 20 percent of the susceptible population over a period of several months.
The KELA, ELISA, IFA, and virus-neutralization tests detect the presence of coronavirus antibodies in a cat. A positive test result only means the cat has had a prior exposure to a coronavirus -- not necessarily one that causes FIP -- and has developed antibodies against that virus. If the test is negative, it means the cat has not been exposed to a coronavirus.
The number, or titer, that is reported is the highest serum dilution that still produced a positive reaction. Low titers indicate a small amount of coronavirus antibodies in the serum, while high titers indicate greater amounts of antibodies. A healthy cat with a high titer is not necessarily more likely to develop FIP or be a carrier of an FIP-causing coronavirus than a cat with a low titer. It also is not necessarily protected against future FIP virus infection.
Recently, two new tests have been developed that can detect parts of the virus itself. The immunoperoxidase test can diagnose FIP more accurately than traditional histopathologic examination because it detects virus-infected cells in the tissue. A biopsy of affected tissue is necessary for evaluation. Another antigen test utilizes polymerase chain reaction (PCR) to detect viral genetic material in tissue or body fluid. Although this test shows promise, PCR is presently only capable of detecting coronaviruses in general, not necessarily those that cause FIP.
There are two primary situations where the determination of coronavirus-antibody titers can be useful to the cat owner or breeder and the veterinarian: • As a screening test, to determine the presence or absence of antibodies in a previously untested household and to detect potential virus carriers or shedders when introducing new cats into households or catteries that are negative for coronavirus antibodies • As an aid (and nothing more than an aid) in the clinical diagnosis of a diseased cat that has signs suggestive of FIP.
Unfortunately, many laboratories use different antigens prepared in different ways, and their interpretation of the assay can differ. False results can occur from nonspecific reactions unless the tests are meticulously controlled. The test can be difficult to interpret, since it usually depends on a subjective decision made by the person reading the test.
A presumptive diagnosis of FIP can usually be made on the basis of clinical signs, routine laboratory tests, and evaluation of abdominal or chest fluid. Some cases, however, present a diagnostic challenge, since the signs of illness are not distinct for FIP. In all cases, a tissue biopsy is the only way to absolutely confirm a diagnosis of FIP.
Currently, FIP is considered to be a routinely fatal disease once a positive diagnosis has been made. Unfortunately, no cure yet exists. The basic aim of therapy is to provide supportive care and to alleviate the self- destroying inflammatory response of the disease. Some treatments may induce short-term remissions in a small percentage of patients. A combination of corticosteroids, cytotoxic drugs, and antibiotics with maintenance of nutrient and fluid intake may be helpful in some cases. In the future, combining immune-modulating drugs with effective antiviral medications may prove to be beneficial for treatment of FIP.
The first FIP vaccine (Primucell FIP by Pfizer Animal Health) was introduced in 1991. It is a temperature- sensitive, modified-live vaccine. The vaccine is licensed for intranasal vaccination of cats at 16 weeks of age, with boosters in 3 to 4 weeks, and then yearly. Once a cat is vaccinated, its serum may have a positive coronavirus antibody titer. This could be a problem for cattery owners who use serologic testing to maintain a coronavirus-free population. The vaccine appears to be safe, but various studies have yielded different estimates of vaccine efficacy. The role that Primucell FIP will ultimately play in protecting cats from FIP is not yet known; for the time being, discussions with your veterinarian should help you decide if your cat should be vaccinated.
Once clinical signs appear, cats with the effusive (wet) form of FIP will live a few days to a few weeks, although some adult cats may linger for six to eight months. Cats with the dry form of FIP usually die within a few weeks, but survival for up to a year or more is possible. Providing good nursing care and feeding a balanced, highly nutritious diet will make your cat more comfortable in the terminal stages of the disease. Your veterinarian may prescribe medications to reduce the discomfort associated with the disease or provide more-specific supportive therapy.
FIP has not been documented in any species other than those of the cat family. FIP is not known to constitute any health risk for human beings. However, FIP virus is similar to a common virus of dogs - canine coronavirus, that produces enteritis in dogs.
