Genogrouping of Vaccine Breakdown Strains (VBS) of Feline Calicivirus in Japan |
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Authors: | K Ohe S Sakai T Takahasi F Sunaga M Murakami A Kiuchi M Fukuyama K Furuhata M Hara Y Ishikawa A Taneno |
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Institution: | (1) School of Veterinary Medicine, Azabu University, Kanagawa;(2) Central Research Laboratories, Intervet Co., Tokyo, Japan |
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Abstract: | Although prevention of feline calcivirus (FCV) infection by vaccination has been attempted, and isolation of FCV, development
of the disease, and a few fatal cases in vaccinated cats have been reported. Fifteen FCV strains isolated from cats that had
been vaccinated with commercially available FCV vaccines (F9, FCV-255, and FC-7) were genogrouped. Molecular analysis of viral
genomes involved the construction of a phylogenetic tree of capsid genes using the NJ method. Cat anti-F9 serum and rabbit
anti-FCV-255 serum were used for virus neutralization tests. Molecular phylogenetic analysis of the amino acid sequences of
15 virus isolates and those of the previously published and GenBank-deposited 9 global and 14 Japanese strains showed that
8 (53%) of the 15 virus isolates as well as the vaccine strains F9 and FCV-255 belonged to genogroup I (GAI), and 7 (47%) belonged to genogroup II (GAII). Of the 8 GAI strains, 2 were isolated from cats that had been vaccinated with an F9 strain live vaccine, 5 from cats vaccinated with
an FCV-255-derived vaccine, and 1 from a cat vaccinated with an FC-7-derived vaccine. Of the 7 GAII strains, 5 were isolated from cats that had been vaccinated with the F9 strain live vaccine, 1 from a cat vaccinated with
the FCV-255-derived vaccine, and 1 from a cat vaccinated with the FC-7-derived vaccine. These results indicate that more vaccine
breakdown strains isolated from the cats vaccinated with the F9 strain-derived vaccine belong to GAII than to GAI, whereas more vaccine breakdown strains isolated from the cats vaccinated with the FCV-255 strain-derived vaccine belong
to GAI than to GAII, and that when the FC-7 strain-derived vaccine is used, the vaccine breakdown strains belong almost equally to GAI and GAII. Thus, the genogroups of virus isolates varied with the vaccine strain used (p < 0.05). On the other hand, the neutralizing titres of feline anti-F9 serum and rabbit anti-FCV-255 serum against the 15
isolates were very low, showing no relationships between neutralizing antibody titres and genogroups. The DNA sequence identities
between the virus isolates and the vaccine strains were low, at 70.6–82.9%, and no strains were found to have sequences derived
from the vaccine strains. Alignment of amino acid sequences showed that the GAI or GAII virus isolates from the F9-vaccinated cats differed at position 428 of the 5’ hypervariable region (HVR) of capsid region
of the F9 strain, whereas those from the FCV-255-vaccinated cats differed at positions 438, 453, and 460 of the 5’HVR of capsid
region E of the F9 strain. We speculate that these differences influence genogrouping. The amino acid changes within the F9
linear epitopes common to G
A
I and G
A
II were noted at positions 450, 451, 457 of 5’HVR of the capsid region E in the isolates from F9-derived vaccine-treated cats,
and 449, 450, and 451 of 5’HVR of capsid region E in the isolates from FCV-255-derived vaccine-treated cats, suggesting that
these amino acid changes are involved in escapes. These results suggest that alternate vaccination with the F9 and FCV-255
strains or the use of a polyvalent vaccine containing GAII strains serves to inhibit development. |
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