TREATMENT

In the past, treatment has focused on two areas—suppressing the immune response or modulating the immune response. The former generally involves administering immunosuppressive drugs to inhibit the immune response, while the latter attempts to enhance the cell-mediated response through the administration of cytokines such as interferon. Immunosuppression by using prednisolone or cyclophosphamide will sometimes slow disease progression but will not provide a cure.³⁷ While human and feline recombinant interferon have been shown to inhibit feline coronavirus replication in vitro, in vivo studies have shown no effect on survival time or quality of life.³⁷

Recently, a new drug tested in three cats with the dry form of FIP demonstrated efficacy in prolonging life and alleviating signs.³⁸ The drug, a polyprenyl immunostimulant, is an investigatory veterinary biologic that upregulates mRNA expression of T helper lymphocytes responsible for effective cell-mediated immunity. In this study, two cats with FIP were still alive two years after diagnosis, while one cat survived 14 months. Further studies are under way to assess this drug's potential for FIP treatment.³⁸

Preventing FIP is challenging since the only effective means of control is preventing infection with feline coronavirus. The widespread nature of the virus and its ease of transmission, as well as the existence of persistent infections, make prevention difficult in a multicat situation. If one cat in a population dies of FIP, the other members are likely already infected with the circulating virus. The likelihood that other cats in the population will develop FIP is not high, but it can occur, especially if there are genetic links to the affected cat.³⁹ There may be some risk to introducing a new cat to this population, but generally, FIP outbreaks are not observed.

Isolating queens and kittens

Various strategies have been used to eliminate or prevent feline coronavirus infection in a cat population. In breeding catteries, isolating pregnant queens nearing parturition and queens and kittens after parturition, as well as early weaning, has been advocated.³⁹ This prevention method, which requires strict quarantine measures and low (< 5) numbers of cats in the population, is designed to delay infection until the kitten is older and can more easily eliminate the virus after exposure.

Removing affected cats from a population

Other means of control involve removing chronic shedders from the population. As mentioned above, this may be done most accurately by using PCR tests to detect virus in feces. Serology may also be helpful, as cats that maintain high antibody levels are likely shedding high levels of virus.³⁹ One of the most important measures that can be used in a breeding cattery is to maintain complete breeding records. Heritability of FIP susceptibility is known to exist; thus, continued breeding of parents, particularly sires that have produced kittens that developed FIP, is not recommended.^26,39

Vaccination

At least one commercially available feline coronavirus vaccine exists. It is an intranasal vaccine containing a temperature-sensitive mutant of feline coronavirus that allows replication in the upper respiratory tract but not systemically. While this vaccine appears to be safe, its efficacy has been questioned. A small reduction in the number of FIP cases was noted in one study when the vaccine was given to seronegative cats.⁴⁰ However, in cats with pre-existing antibody, the vaccine showed no protection.

In households in which feline coronavirus is endemic or in which FIP has occurred, most cats are seropositive and, thus, not aided by vaccination. Kittens at highest risk for FIP are those born into colonies in which the virus is endemic, where infection often occurs by 4 to 6 weeks of age.⁴ However, the vaccine is not given until 16 weeks of age; thus, the vaccine is of dubious usefulness in those situations in which the risk is greatest. It may provide some protection for seronegative cats entering an infected population, but currently, this vaccine is not recommended as part of core vaccines for routine use.⁴¹