Infectious coryza (IC) is an important respiratory infectious disease in chickens. In this study, an Avibacterium paragallinarum Page serovar C strain, named ZJ-C, was isolated from a local layer flock that was routinely vaccinated with an inactivated trivalent vaccine, using reference strain Modesto as the serovar C immunogen. The pathogenicity, immunogenicity, and genetic characteristics of ZJ-C were studied. The minimum pathogenic dose of the isolate was 100 CFU, which was 1/1,000 of the dose of the serovar C reference strain Modesto. The vaccination-challenge trial in specific pathogen-free (SPF) chickens showed that the ZJ-C bacterin could provide 100% protection against challenge from both ZJ-C and Modesto strains, whereas Modesto provided 100% protection against challenge from itself, but only 70% protection against ZJ-C. Sequence analysis of the HMTp210 hypervariable region (region 2) showed that the homology of region 2 between ZJ-C and Modesto was 96.14%, whereas the homology between ZJ-C and the Kume serovar C-4 reference strain HP60 was 99.83%. Phylogenetic analysis of region 2 showed that ZJ-C was most closely related to cluster C-4, represented by HP60. The experimental data obtained in this study will help the selection of optimal vaccine strains and assist serotyping studies of Av. paragallinarum.
Keywords: Avibacterium paragallinarum; HMTp210 hypervariable region; characterization.
Vaccination with inactivated multivalent vaccines is a primary strategy to control Infectious coryza. Avibacterium paragallinarum serotyping is important for effective protection as inactivated whole-cell vaccines provide protection against only the serogroup or serovar from which the vaccine was derived. In this study, a novel serovar within the serogroup C Avibacterium paragallinarum isolate ZJ-C has been characterized first time in China. It was highly virulent and induced 100% cross-protection to Modesto bacterin vaccinated chickens, but not the other way around.
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