Molecular characterization of the HMTp210 gene of Avibacterium paragallinarum and the proposition of a new genotyping method as alternative for classical serotyping

Avibacterium paragallinarum (A. paragallinarum) is the aetiological agent of infectious coryza (IC) in chickens and characterized by acute respiratory distress and severe drop in egg production. Vaccination is important in the control of IC outbreaks and the efficacy of vaccination is dependent on A. paragallinarum serovars included in the vaccine. Classical serotyping of A. paragallinarum is laborious and hampered by poor availability of antigens and antisera. The haemagglutinin, important in classical serotyping, is encoded by the HMTp210 gene. HMTp210 gene analysis has been shown to have potential as alternative to classical serotyping. The aim of the present study was to further investigate the potential of sequence analyses of partial region 1 of the HMTp210 gene, the HMTp210 hypervariable region and the concatenated sequences of both fragments. For this analysis, 123 HMTp210 gene sequences (field isolates, A. paragallinarum serovar reference strains and vaccine strains) were included. Evaluation of serovar references and vaccine strains revealed a need for critical evaluation, especially within Page serovar B and C. Phylogenetic analysis of HMTp210 region 1 resulted in a separation of Page serovar A, B and C strains. Analysis of the HMTp210 HVR alone was not sufficient to discriminate all nine different Kume serovar references. The concatenated sequences of HMTp210 region 1 and HMTp210 HVR resulted in 14 clusters with a high correlation with Page serovar and with the nine currently known Kume serovars and is therefore proposed as a novel genotyping method that could be used as an alternative for classical serotyping of A. paragallinarum.