Feline infectious peritonitis (FIP) is a relatively new cat disease, recognized as clinically significant in late 1950s. Despite the fact that it is one of the most researched infections in cats it continues to be a major killer of young cats.Feline infectious peritonitis is a coronaviral disease that can affect cats of any age, but is most prevalent among cats under three years of age, especially from 4 to 16 months of age. It refers to the more common effusive (wet, nonparenchymatous) form of the disease – a transmissible inflammatory condition of the visceral serosa and omentum with exudation into the abdomen. A second form, granulomatous FIP is called ‘dry’, parenchymatous, or non-effusive because there is no inflammatory exudation into body cavities.
FIP virus (FIPV) arises through specific mutations in a common feline enteric coronavirus (FECV) that is ubiquitous in cats throughout the world and not in itself an important pathogen. FECV is shed in the feces of most apparently healthy cats within large, multi-cat environments.
Feline infectious peritonitis occurs commonly in catteries, shelters, kitten foster/rescue facilities and dense free-roaming colonies. The incidence is significantly higher among kittens and younger cats. The mortality is extremely high once clinical signs appear, although some cats can live with the disease for weeks, months or, rarely, years. An average of one to five percent of young cattery or shelter cats will die from FIP, with losses in catteries higher than shelters. In some cases of enzoonotic outbreaks, a mortality rate of >10% was noted.
No treatment has proven effective in curing FIP and a successful vaccine has not been developed. Cats that develop FIP inevitably die of their disease in days, weeks or months.
Abyssinians, Bengals, Birmans, Himalayans, Ragdolls and Rexes have a higher risk, whereas Burmese, Exotic Shorthairs, Manxes, Persians, Russian Blues and Siamese cats are at a decreased risk of FIP infection. One of the most significant factors appears to be genetic susceptibility, which accounts for up to 50% of the incidence.
Protective immunity to feline infectious peritonitis
Protective immunity to FIP is thought to result mainly from cell-mediated immunity and also depends on the expression of several citokynes. Recently, with use of genetic testing, polymorphisms in genes involved in cell-mediated immunity were associated with FIP.
Polymorphism in the feline interferon-gama (fFING) gene was associated with increased resistance to the development of FIP. Subsequently, more factors that could be involved in infection development were investigated.
The tumor necrosis factor-alpha (fTNFA) gene and the fCD209 gene that codes for a specific adhesion molecule which affects the binding and infection of feline coronavirus, were found to be associated with FIP. A specific polymorphism in the TNFA gene and two separate polymorphisms in the fCD209 gene were also found to be associated with increased resistance to infection. In addition to variants responsible for increased immunity to FIP, two polymorphisms in fCD209 were associated with increased susceptibility to infection.
Genetic test available for FIP protection
According to recent findings, genetic tests have been developed. The results of DNA tests for these variants can help breeders to avoid losses from FIP in their catteries. By applying DNA test results to breeding plans, a population with increased resistance to FIP can be bred.
Genetic testing allows us to detect protective polymorphisms. The combination of only six polymorphisms cannot ensure complete protection from FIP infection, but it can greatly reduce the probability of developing FIP.