Gene specific assay to differentiate strains of pseudorabies virus

The need for compatibility between Pseudorabies vaccination and disease eradication measures has caused the production and release of diverse Pseudorabies virus (PRV) vaccine strains with altered genetic makeups due to the deletion of specific genes. These genes code for antigens used as differential serologic markers. By use of polymerase chain reaction (PCR), it is possible to determine, in a rapid and sensitive way, if a given PRV strain has a "wildtype" genotype, or if instead it carries a deletion for a specific gene. A sequence of 217 bp was selected as an amplification target within the gene of the essential glycoprotein 50 (gp50). Another sequence of 173 bp was selected in the joint area of glycoprotein 63 (gp63) and glycoprotein I (gI) genes. Under optimal amplification conditions, the simultaneous use of both PCR tests allowed us to differentiate specifically gI negative strains from several other wild type PRV strains, utilizing cell culture-propagated virus, acutely and latently infected neural tissue of mice and pigs as source of DNA targets. This kind of test will be useful for the rapid identification of PRV strains detected in tissues from individual animals, especially in cases of single reactors occurring in vaccinated herds. At the same time, the gene-defined PCR test will be useful for the evaluation of vaccines in their ability to prevent latency, by permitting unequivocal differentiation between vaccine and challenge virus strains.