Characterization of isolates of Haemophilus paragallinarum from Argentina

The biochemical and serological properties of Haemophilus paragallinarum isolates recovered from 11 recent outbreaks of infectious coryza in layer hens and one case of swollen-head syndrome in broilers in Argentina are described. Twenty-four isolates had the typical biochemical properties of H. paragallinarum. All isolates were serotyped according to the Page scheme. Ten of the isolates were serovar A, 11 were serovar B, one was serovar C, and two isolates could not be serotyped. The isolates were also examined using a panel of monoclonal antibodies (MAbs) for Page serovars A (one MAb available) and C (three MAbs available). The serovar B isolates all failed to react with any MAb. The serovar C isolate reacted with all three serovar C MAbs but not with the serovar A MAb. Only six of the 10 serovar A isolates reacted with the serovar A MAb. These results indicate that H. paragallinarum isolates from Argentina are antigenically distinct from those examined in other countries, and it is suggested that coryza vaccines intended for use in Argentina may be more effective if based on local strains.