A Comparison Involving a Wild-Type Strain of Pseudorabies Virus (Rice) and a Vaccine Strain of Pseudorabies (Norden) Using Methods of Restriction Enzyme Mapping and DNA Sequencing

Abstract

Pseudorabies virus (PrV), a member of the herpesvirus sub-family alphaherpesvirinae, causes the illness known as Aujezsky's disease. PrY is virulent in all mammals, with the exception of the higher primates, i.e the great apes and humans. The virus is responsible for an economic loss exceeding $100 million annually through the infection of livestock, the primary target animals of PrY. As the adult pig is capable of surviving infection, with the virus often going latent, it serves as the primary reservoir of Pr V. Several attenuated vaccine strains of PrY are currently being marketed in the United States and Europe, one of which, PrY Norden, contains a 3.5-Kb deletion in the Us portion of its genome, in comparison to the wild-type strain of PrY, Rice. It has been shown previously that this deletion is at least partially responsible for Norden's avirulence in pigs. Through the comparison of PrY Norden with the wild-type strain of PrY, Rice, this study has determined the precise location of this deletion using methods of restriction enzyme mapping and end-labeled DNA sequencing. The results generated in this study indicate that the genes which code for the viral envelope glycoproteins gX, gp50, and gp63 are not affected by the Us deletion, but that the gene which codes for the glycoprotein gI has been deleted, as well as a series of genes whose functions are unknown. The deletion begins in the region of BamH I 7, 77 bases downstream from the gp63 termination codon, and extends 5OO bases into the region of BamH I 12. In addition to the characterization of the Norden Us deletion, several restriction maps have been constructed using a series of restriction endonucleases which were largely untested on PrY DNA. The generation of such restriction maps has illustrated several regions of heterogeneity between the two strains, and should prove useful in future comparisons of the two strains of PrY.