Using CF0218-ELISA to distinguish Chlamydophila felis-infected cats from vaccinated and uninfected domestic cats

Chlamydophila felis is a causative agent of acute and chronic conjunctivitis and pneumonia in cats. Cats can be vaccinated with killed or attenuated C. felis. However, current serodiagnostics cannot distinguish these cats from naturally infected cats. This causes difficulty of early diagnosis and seroepidemiological survey for C. felis. We previously reported that C. felis CF0218 can be used as a C. felis-infection-specific diagnostic antigen in experimentally infected and/or vaccinated cats. In this study, we evaluated an enzyme-linked immunosorbent assay using recombinant CF0218 as antigen (CF0218-ELISA) to detect anti-C. felis antibody in 714 sera of domestic cats whose histories of vaccination against C. felis are known. The 44 vaccinated cats were 93% negative using CF0218-ELISA; half of these scored positive by immunofluorescence assay (IFA) using C. felis-infected cells as antigen. The 670 non-vaccinated cats had CF0218-ELISA positivity rates that were statistically in agreement with IFA (18% vs. 21%). These results show that CF0218, which was identified as a C. felis-infection-specific antigen, is a useful serodiagnostic antigen to distinguish naturally C. felis-infected cats from vaccinated and non-infected cats.