Genotypic diversity of Haemophilus parasuis field strains.

Haemophilus parasuis is the cause of Glässer's disease and other clinical disorders in pigs. It can also be isolated from the upper respiratory tracts of healthy pigs, and isolates can have significant differences in virulence. In this work, a partial sequence from the 60-kDa heat shock protein (Hsp60) gene was assessed as an epidemiological marker. We analyzed partial sequences of hsp60 and 16S rRNA genes from 103 strains of H. parasuis and other related species to obtain a better classification of the strains and examine the correlation with virulence. The results were compared with those obtained by enterobacterial repetitive intergenic consensus PCR. Our results showed that hsp60 is a reliable marker for epidemiological studies of H. parasuis and that the analysis of its sequence is a better approach than fingerprinting methods. Furthermore, the analysis of the hsp60 and 16S rRNA gene sequences revealed the presence of a separate lineage of virulent strains and indicated the occurrence of lateral gene transfer among H. parasuis and Actinobacillus strains.