Comparison of theVirulence in Mice and Piglets.

Abstract

In this study, we compared the virulence of the most common serovars ofin China, serovars 4, 5, 12, and 13 (36 strains in total) in BALB/c mice and piglets. In mice, the median lethal doses (LDs) of the four serovars were roughly 9.80 × 10-4.60 × 10CFU, 2.10 × 10-8.85 × 10CFU, 4.81 × 10-7.01 × 10CFU, and 1.75 × 10-8.45 × 10CFU, respectively. Serovar 13 showed the strongest virulence, followed by serovar 4, serovar 12, and serovar 5, but a significant difference in virulence was only observed between serovars 5 and 13. The virulence of strains of the same serovars differed significantly in piglets. Virulent and attenuated strains were present in all serovars, but serovar 5 was the most virulent in piglets, followed by serovars 13, 4, and 12. A significant difference in virulence was observed between serovars 5 and 4 and between serovars 5 and 12. However, the virulence of serovars 5 and 13 did not differ significantly. This comprehensive analysis ofvirulence in mice and piglets demonstrated that: (1) the order of virulence of the four domestic epidemic serovars (from strongest to weakest) in piglets was serovars 5, 13, 4, and 12; (2) both virulent and attenuated strains were present in all serovars, so virulence did not necessarily correlate with serovar; (3) Althoughwas fatal in BALB/c mice, its virulence is inconsistent with that in piglets, indicating that BALB/c mice are inadequate as an alternative model ofinfection.