In vitro comparison between four variants of Aujeszky's disease virus

Four Aujeszky's disease (pseudorabies) virus variants were characterized in vitro by investigation of their resistance to heat at 48 degrees C, sensitivity to trypsin and ability to replicate in pig alveolar macrophages, two of these variants (Ls-1 and Ls-2) were cloned previously from a single isolate of virus and showed differing pathogenicity for pigs; the virulent Stanley strain; and the non-virulent NIA-4 strain were included for comparison. Heat treatment produced slight decreases in infectivity but no significant differences were observed in the rates of inactivation. Both Ls-1 and Ls-2 were significantly more sensitive to trypsin treatment than the other two. The comparison of progeny virus titres after replication in alveolar macrophages allowed further differentiation among variants. Ls-1 and Ls-2 had similar titres in cultures infected with high virus input but in cultures infected with low virus input (0.1 TCID50/cell) Ls-1 produced higher titre. The difference in titres at 48 h post-infection was statistically significant (P less than 0.05). The cytopathogenicity for macrophages of the strains was correlated with their virulence for pigs, Stanley strain being the most cytopathogenic and NIA-4 the least.