VACCINE GENOTYPE AND ROUTE OF ADMINISTRATION AFFECT PSEUDORABIES FIELD VIRUS LATENCY LOAD AFTER CHALLENGE

The influence of vaccine genotype and route of administration on the e fficacy of pseudorabies virus (PRV) vaccines against virulent PRV chal lenge was evaluated in a controlled experiment using five genotypicall y distinct modified live vaccines (MLVs) for PRV. Several of these MLV s share deletions in specific genes, however, each has its deletion in a different locus within that gene. Pigs were vaccinated with each va ccine, either via the intramuscular or intranasal route, and subsequen tly challenged with a highly virulent PRV field strain. During a 2-wee k period following challenge with virulent PRV, each of the vaccine st rains used in this study was evaluated for its effectiveness in the re duction of clinical signs, prevention of growth retardation and virule nt virus shedding. One month after challenge, tissues were collected a nd analyzed for virulent PRV latency load by a recently developed meth od for the electrochemiluminescent quantitation of latent herpesvirus DNA in animal tissues after PCR amplification. It was determined that all vaccination protocols provided protection against clinical signs r esulting from field virus challenge and reduced both field virus shedd ing and latency load after field virus challenge. Our results indicate d that vaccine efficacy was significantly influenced by the modified l ive vaccine strain and route of administration. Compared to unvaccinat ed pigs, vaccination reduced field virus latency load in trigeminal ga nglia, but significant differences were found between vaccines and rou tes of administration. We conclude that vaccine genotype plays a role in the effectiveness of PRV MLVs. (C) 1998 Elsevier Science B.V. All r ights reserved.