Designation of 15 serovars of Haemophilus parasuis on the basis of immunodiffusion using heat-stable antigen extracts.

Previous independent investigations of the serotyping of Haemophilus parasuis strains have led to the designation of serovars A to D, 1 to 7, Jena 6 to Jena 12, and ND1 to ND5. Heat-stable antigen preparations from the reference strains for these serovars were tested by immunodiffusion with rabbit hyperimmune antisera. The existence of 15 distinct serologic groups was apparent, for which we propose the designations serovars 1 to 15. Examination of 290 field isolates from swine in the former German Democratic Republic indicated a prevalence of serovars 4 and 5, which together accounted for 41% of the isolates examined. However, 26.2% of the isolates were nontypeable with this test procedure and available antisera. Intraperitoneal inoculation of specific-pathogen-free pigs with cells representing the 15 serovars indicated differences in virulence which may be serovar related. Cells of strains representing serovars 1, 5, 10, 12, 13, and 14 were the most virulent, causing death or moribundity in inoculated pigs. Cells of serovars 2, 4, 8, and 15 caused polyserositis, but not death, in inoculated pigs. However, inoculation of cells of strains representing serovars 3, 6, 7, 9, and 11 resulted in no clinical symptoms or lesions indicative of H. parasuis infection.