Immunological and Genetic Characterization of Feline Caliciviruses Used in the Development of a New Trivalent Inactivated Vaccine in Japan

Although vaccination against feline calicivirus (FCV) infection is widespread in Japan, FCV-associated diseases are still a significant problem in cats. Thus, we developed a new trivalent inactivated vaccine, Kyoto Biken Feline-CPR, consisting of three FCV strains; one was the production strain of our previous vaccine, and the others were screened from 60 field isolates obtained between 1998 and 2000 based on cross-neutralization tests. In this report, the three FCV strains used for development of the new vaccine were antigenically and genetically characterized. The three strains were antigenically quite different, as revealed by cross-neutralization tests. Alignment of deduced amino acid sequences of capsid regions A to E revealed that there were marked differences between the strains in both the N- and C ends of region E. Antisera against the three vaccine strains, our new vaccine and 2 commercial vaccines were then evaluated for neutralization with 58 field isolates collected between 2003 and 2006. Rat antisera against the three vaccine strains and a mixture of the 3 strains neutralized 49, 37, 42 and 55 isolates, respectively. Cat antiserum against the new vaccine neutralized 50 (86.2%) isolates, whereas the numbers neutralized by cat antisera against 2 commercial vaccines were 37 (63.8%) and 25 (43.1%). In conclusion, the immunological and genetic properties of the 3 vaccine strains investigated varied widely, and the Kyoto Biken Feline-CPR vaccine may have more potential to meet the antigenic diversity of FCVs spreading throughout Japan.