Feline Infectious Peritonitis (FIP)
Feline Infectious Peritonitis (FIP) Virus is a coronavirus. There are many strains of feline coronaviruses. Strains that cause a mild intestinal disease (diarrhea) are called Feline Enteric Coronavirus (FECV). Strains that cause FIP are thought to be a form of the enteric virus (FECV) that mutates into the lethal FIPV due to environmental and genetic factors in the affected cat. FECV and FIPV are connected because all cats that have FIPV also have FECV. The opposite is not true.
FECV is widespread in the cat population. Feral or free roaming cats have an FECV incidence of about 30%. Catteries where there is a dense population of genetically related cats can have an incidence of FECV of about 100%. The same is true for households with more than 6 unrelated cats. Households with 3-4 cats have a 75% incidence of FECV. The FECV can spread from cat to cat through contact with infected feces, water bowls, articles of clothing, litter and litter pans, etc.
The incidence of FIPV on the other hand, does not follow the same infectious pattern. In fact, FIP is not considered an infectious disease. If one cat in a house dies of FIPV, this does not increase the likelihood that another cat in the same house will die of the disease. There may be houses where several or all cats are positive for FECV, but none or only one cat gets FIPV. This pattern of disease fits more with the concept that FECV may mutate or change to a lethal FIPV within an individual cat. Whether this mutation occurs depends on a cat's genetic make-up, immune function, state of health, age and the stresses the cat experiences. There is an age-related resistance to FIP. The most susceptible to FIP are very young cats (under 1 year) and the very old.
Testing for feline coronaviruses is frustrating. There are no tests that distinguish FECV from FIPV. Tests that look at the number of antibodies produced (this is called a titre) by a cat against the coronavirus only indicate that the cat has been exposed to a coronavirus. It does not give any indication as to the likelihood that the cat will develop FIP. Several things can cause a high coronavirus antibody count (or titre) in a cat. These include: 1) vaccination for FIP, 2) vaccination against other unrelated diseases. To further complicate things, some cats can shed coronavirus but never mount an immune response so they will have low coronavirus titre.
Recently, a DNA-based test has been developed. This type of test identifies the actual presence of the coronavirus itself, as opposed to identifying the cat's response (antibody titre) to the virus. The DNA based tests do not yet distinguish FECV from FIPV. Also, false negatives can occur. That is to say that some cats that succumb to FIPV have tested negative for coronavirus with the DNA based test. At present, there is no perfect test for the feline coronavirus.
A cat with FIPV does have characteristic changes in infected tissues (kidney, spleen, liver). By taking a sample of these tissues (surgically or after the cat is dead) a definative diagnosis of FIPV can be made by examining the tissue at the microscopic level.
Cats recently infected with the FECV virus often have mild or no clinical signs. They may experience upper respiratory signs (sneezing, watery eyes) or intestinal signs (diarrhea). Usually cats make a complete recovery from this primary infection; although some will go on to become reinfected and some will become carriers of the virus. Unfortunately, a few cats will experience the lethal disease of FIP. This may occur weeks to years after the initial infection.
The lethal form of FIP may have a sudden or insidious onset. The two main forms of FIP are the dry and wet (or effusive) forms, although a cat may develop a combination of these two forms. Cats that get these forms of FIP have very active immune responses, but they are ineffective at neutralizing the virus. It is their active, but futile, immune response that contributes to many aspects of the clinical disease. The result of the ineffective immune response is vasculitis (inflammation in and around the blood vessels). This inflammatory process makes the vessels leaky and fluid escapes. In the wet form, fluid accumulates in the abdomen or chest, often making breathing difficult. The wet form is 4 times more common than the dry form. The dry form usually has a slower onset. The body compensates for the damaged vessels and the 'leakiness' is controlled, although the inflammation still proceeds. The cat usually experiences loss of appetite and weight, dull hair coat, depression, anemia and fever. This progresses to organ failure of the kidneys, liver, pancreas and neurological system. The signs an infected cat exhibits at this stage mimic numerous other disease processes and can make the diagnosis of FIP difficult.
To assess whether a cat's signs are compatible with FIP, a veterinarian will consider several things including the cat's lymphocyte (a type of White Blood Cell) numbers, globulin levels, physical findings and possibly the results of antibody titres and the coronavirus DNA based test.
There is no effective cure or treatment of FIP. Supportive care is aimed at making the cat as comfortable as possible and treating the signs that arise. This may involve immunosuppressive medication and removal of excess fluid accumulation. These measures only treat the cat's signs, they do not stem the progression of the disease.
Development of FIPV in a cat depends on that cat's individual gentic make-up and to some extent, environment. To prevent the disease, breeders should aim at breeding cats with a natural ability to avoid the disease and elect not to breed cats that produce FIP susceptible offspring. This involves keeping detailed records on the disease status of their own animals and of the kittens they sell. People who live in multicat households should take care when introducing a new (especially young or old) cat into their household. If this new cat comes from an environment where it has likely been exposed to FECV, it is likely safe. If it has never been exposed to the virus, this new cat may have problems, especially if it is younger than a year, or very old. Prevention also involves attention to hygiene and cleanliness, reducing the "stress" in the cat's environment, and minimizing exposure to other diseases, especially Feline Leukemia Virus and Feline Immunodeficiency Virus.
There is an intranasal vaccination available for FIP for cats over 16 weeks of age. It appears to be safe, but different studies show various levels of efficacy of the vaccine. Also, kittens are usually infected with FECV by 10 weeks of age. Once exposed to FECV, there is no need to vaccinate the cat. So many kittens will aready be exposed before they are able to be vaccinated. Vaccinated cats will have a positive coronavirus titer. If a breeder or multicat owner uses titers as the basis for accepting or rejecting a cat into the household, vaccination may confuse this method of screening.
For more information on FIP, visit the Cornell Feline Health Center Web Site, and talk to your veterinarian.