Is recombination of PRV vaccine strains a real problem?

Simultaneous inoculation of 50 doses of two modified live pseudorabies vaccines with either functional (strain Bartha) or inactivated (strain Begonia) thymidine kinase into piglets of 1 week of age did not induce any clinical signs of Aujeszky's disease. In only 3% of the cases could virus be re-isolated from organ specimens, namely from trigeminal ganglia or tonsils. In all samples only Bartha strain was recovered. By using a nested set of gII-specific primers viral DNA was found in 92% of the 135 samples. A deletion of 72 bp in the inverted repeats was used to differentiate Begonia from the Bartha strain. The genomes identified represented 12 times the Bartha, and 11 times the Begonia type, the remaining genome types could not (yet) be identified. We found no indications for the presence of the genomes of both viruses at the same time, nor for recombinants. The results suggest no selective pressure for recombinants by using vaccines with the same marker, i.e. gI-negative vaccines. Thus, when using gI-minus vaccines only, there are no indications that any real problems of recombination should arise.