Immunization against feline coronaviruses.

Feline infectious peritonitis (FIP) is caused by one of several strains of feline coronaviruses which are grouped into 2 general types of viruses. Infection of cats with FIP virus results in production of serum antibodies which may be protective in conjunction with cell mediated immunity, may provided no protection at all, or may produce an immune enhancement to subsequent exposure to another FIP virus or a recrudescence of the original infecting virus. Attempts at immunization of cats against FIP with inactivated or live FIP viruses have been generally unsuccessful, and often sensitizing the cat through immune enhancement rather than providing protection. Heterologous live virus vaccines using viruses of the same antigenic cluster (transmissible gastroenteritis of swine, canine coronavirus, and human coronavirus 229E) have failed to provide protection against FIP virus. Further research into the exact mechanism of protection and immune enhancement is needed in order to understand ways of producing an effective and safe vaccine.