Abstract: In this study, we compared the virulence of the most prevalent Haemophilus parasuis (36 strains) serovars 4, 5, 12, and 13 in China in BALB/c mice and piglets models. The results of mice virulence tests showed that the LD₅₀values of the four serotype strains were 9.80×10⁷-4.60×10⁹CFU (serovar 4),2.10×10⁸-8.85×10⁹ CFU (serovar 5),4.81×10⁷-7.01×10⁹ CFU (serovar 12) and 1.75×10⁸-8.45×10⁸ CFU (serovar 13), respectively. Serovar 13 was the most highly virulent serovar in mice, followed by serovars 4, 12, 5. However, there was a significant difference in virulence only between serovars 5 and 13 (P<0.05).The results of piglet virulence tests showed that the virulence of different strains in the same serovar were remarkably different, including virulent strains and weak strains. Serovar 5 was the most highly virulent in piglet, followed by serovars 13, 4, 12,but there were significant differences between serovars 5 and 4 (P=0.039), serovars 5 and 12 (P=0.033), and there was no significant difference between serovars 5 and 13 (P=0.241). Comparing the results of HPS virulence tests on mice and piglets, three conclusions can be drawn:first, the overall virulence of the four domestic epidemic serotypes from strong to weak were serovars 5, 13, 4 and 12 in turn; Second, there were both strong and weak strains in the same serotype, so there was no correlation between the serovar and virulence of HPS. Third, although HPS can kill BALB/c mice, its virulence result was not consistent with the piglet virulence test, indicating that it has some defects as an alternative model.

Key words: Haemophilus parasuis, serotype, virulence, mice, piglet, correlation