Introduction Feline infectious peritonitis (FIP) is a severe progressive debilitating disease caused initially by a viral infection (feline enteric corona-virus (FECV)) and then by the body's own immune system. Although FIP was first reported in 1963, there are reports of clinical cases that are likely to be FIP going back to as earlier as 1914. The common benign form of feline corona-virus is referred to as FECV. When FECV has mutated into a disease-causing form, it is then referred to as FIPV (feline infectious peritonitis virus). FIP is the term for clinical disease associated with FIPV infection. FIP is one of the most important viral infections of cats because the disease is almost invariably fatal. The disease is most feared in catteries, as most catteries that remain operative for several years will have a brush with FIP. Despite the fact that this disease is a shared experience in the cat fancy, affected catteries are often wrongly feared and ostracized. All breeders must thus make the effort to understand this disease and how to control it. Feline corona-virus is different from any other feline virus in several important ways: Â· Antibodies in the cat have no protective function for the cat and may play a role in the disease FIP itself. Â· Antibody titres are meaningless for diagnosis or prognosis. Â· A vaccine is available, but there is no consensus on its efficacy or safety. What causes FIP Feline corona virus is a common and highly infectious feline virus, belonging to the genus Corona-virus, which has members that infect other species (man, swine, cattle, birds, dogs). Many different strains of corona-virus are capable of infecting cats, but most do not produce serious disease. The majority of cats with FECV (about 95% or more) remain healthy. But in a small number of cases, FECV infection is the first step in a chain of events leading to FIP. This happens because corona viruses are made of large numbers of nucleotides, the basic unit of genetic material, and they are prone to mutations. As the virus reproduces itself, errors are made in copying these nucleotides. The more nucleotides, the more errors are possible. While most of these errors are harmless, some will have the effect of giving FECV the ability to cause disease. These mutant FECV strains are called FIP virus. FIP-producing strains are distinguished by their ability to invade and grow in certain white blood cells, which then transport the virus throughout the cat's body. An intense inflammatory reaction follows in the tissues where these virus-infected cells locate. It is thus this interaction between the body's own immune system and the virus that is responsible for the disease. Some cats will mount an effective immune response that prevents viral spread in the body and stops disease developing whereas, in others, the virus is able to multiply and cause severe disease that is ultimately lethal. Recent research has shown that mutant FECVs arise within an individual cat. Therefore the vast majority of cats do not "catch" FIP, but they develop it themselves from their own mutant FECV. Transmission of FIP from cat to cat is therefore considered to be rare. This fact has caused leading FIP researchers to state that cats who are ill with FIP are unlikely to be a risk to other cats and thus do not need to be isolated. Catteries are especially likely to be FECV positive since traffic of cats and kittens in and out of the establishment is common. However, the incidence of cases of FIP is quite low in comparison but losses can be sporadic and unpredictable. The peak ages for losses to FIP are from 6 months to 2 years old (with the highest incidence at 10 months of age). Age-associated immunity to FIP appears to be possible. Transmission of FIP from a queen to her unborn kittens has not been shown to occur. How do cats get FIP? Feline corona-virus is ubiquitous among cats and is extremely common where large numbers of cats are kept together. At least 30 - 50% of pet cats are likely to have been exposed to this virus and where large groups of cats are kept together, typically 80 - 100% of them will have been infected at some stage. FECV is present in the saliva and faeces of infected cats and some cats will shed the virus for many months. 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. The virus can survive for a number of weeks in the environment, but is rapidly inactivated by most household detergents and disinfectants. Many different strains of the virus exist and, fortunately, most of these do not cause serious disease. The vast majority of infections therefore result in no signs, or possibly just some mild self-limiting diarrhoea. Clinical signs of FIP Initial exposure to the corona virus usually results in no obvious clinical disease, although some cats may experience 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 will go on to develop the lethal disease: weeks, months, or perhaps years after the primary infection. When a cat develops FIP, the virus has disseminated and replicated throughout the body, resulting in severe inflammation at a number of different sites. Clinical signs vary depending on the major site(s) of inflammation. 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 non-specific 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. The onset of noneffusive FIP is usually slower. Fluid accumulation is minimal, although weight loss, depression, anaemia, and fever are almost always present. Signs of kidney failure (increased water consumption and urination), liver failure (jaundice), pancreatic disease (vomiting, diarrhoea, diabetes), neurological disease (loss of balance, behavioural changes, paralysis, seizures), enteritis (vomiting, diarrhoea), or eye disease (inflammation, blindness) may be seen in various combinations. Thus FIP is often a difficult disease to diagnose because each cat can display different signs that are similar to those of many other diseases. How common is FIP? Fortunately, the vast majority of cats that are infected with feline corona-virus do not develop FIP. This is because most strains of corona-virus do not cause severe disease and most cats are able to develop a good immune response to infection. In the general cat population, FIP is quite rare and probably accounts for considerably less than 1% of severe disease seen in cats. However, FIP is more common in young cats, particularly in those below 1 - 2 years old (where the immune response is less well developed), in stressed cats, or those with concurrent disease. The disease is also more common in multi-cat households, shelters and catteries, where up to 10% or more of the cats can die from FIP. Diagnosis of FIP One of the most difficult aspects of FIP is that there is no simple diagnostic test. Exposure to corona-virus infection can be established by detecting antibodies to the virus in a blood sample (corona-virus serology). However, this does not allow distinction between past and current infection and cannot differentiate between strains of corona-virus. Thus, while very many cats have antibodies to FECV, very few of these cats ever develop disease. More sophisticated tests are now available to detect the presence of virus in blood samples but, again, these tests cannot differentiate between different strains of corona-virus. To date, there is no way to screen healthy cats for the risk of developing FIP and the gold standard for the diagnosis remains a biopsy or findings at necropsy. The ELISA, IFA, and virus-neutralisation tests detect the presence of corona-virus antibodies in a cat. A positive test result only means the cat has had a prior exposure to a corona-virus, 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 corona-virus. The number, or titre, that is reported is the highest dilution that still produced a positive reaction. Low titres indicate a small amount of corona-virus antibodies in the blood, while high titres indicate greater amounts of antibodies. A healthy cat with a high titre is not necessarily more likely to develop FIP or be a carrier of FIP-causing corona-virus than a cat with a low titre. It also is not necessarily protected against future FIP virus infection. On routine blood tests a number of changes commonly occur in FIP and, although not specific for the disease, they can help in the diagnosis. A presumptive diagnosis can often be made on the basis of clinical signs, routine blood tests, corona-virus serology and analysis of accumulated fluid (if present). However, at best this can only give a presumptive diagnosis. Definitive diagnosis requires examination of affected tissues (biopsy or post mortem examination). Recently, two new tests have been developed that can detect parts of the virus itself. The immunoperoxidase test detects virus-infected cells in the tissue. However, a biopsy of affected tissue is necessary for evaluation. Another antigen test utilises 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 corona viruses in general, not necessarily those that cause FIP. One major benefit of the PCR test is that it may be used on body fluids, such as effusions from the chest or abdomen of a sick cat. If virus is found in these fluids, it strongly supports the presumptive diagnosis of FIP. Therapy There is no cure for FIP and once clinical signs develop it is almost invariably fatal. Supportive therapy (e.g. nutritional support and anti-inflammatory drugs) may result in temporary improvement and can be used if the signs are not too severe. However, to date, no therapy has been shown to have long-term beneficial effects. 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 cats. In the future, combining immune-modulating drugs with effective antiviral medications may prove to be beneficial for treatment of FIP. Prevention In multi-cat environments, minimising overcrowding, ensuring the environment is kept clean (disinfecting with dilute household bleach where possible), minimising stress, and other diseases will all help to reduce the risk of FIP developing. In other countries a vaccine is also available to help protect against FIP. However, this vaccine is not currently available in South Africa, does not provide 100% protection against the disease, and there is no consensus on its efficacy or safety.