TRANSMISSION OF 2 PSEUDORABIES VIRUS-STRAINS THAT DIFFER IN VIRULENCEAND VIRUS EXCRETION IN GROUPS OF VACCINATED PIGS

Objective-To determine whether 2 pseudorabies virus (PRV) strains that differ in virulence differ in transmission among vaccine strain 783-i noculated pigs. Design-Three experiments were conducted, each with 2 g roups of 10 pigs inoculated with the glycoprotein E-negative vaccine 7 83. In the first 2 experiments, half of one group was inoculated with the mildly virulent strain Sterksel, and half of the other group was i noculated with the virulent strain NIA-3. The remaining pigs were cont act-exposed to the inoculated pigs. In the third experiment, 2 pigs in each group were inoculated with strain NIA-3, and the other 8 pigs in each group were contract-exposed to these 2 pigs. Animals-Specific-pa thogen-free pigs that were seronegative for antibodies to PRV. Procedu re-Estimation of the transmission of virus in each group was based on a stochastic model, in which the observable variable was the number of contact infections. The sole parameter of the model was the reproduct ion ratio theta. A glycoprotein E ELISA was used to determine whether infection occurred. Virus excretion in the oropharyngeal fluid was det ermined by plaque assay to measure infectivity. Results-Vaccinated pig s had a significant difference in virus excretion between the mildly v irulent and virulent strains. Sterksel strain-inoculated pigs shed sig nificantly more virus than did NIA-3 strain-inoculated pigs. Despite t his difference in virus excretion, the 2 strains did not differ in tra nsmission.Conclusions-Both PRV strains would be eliminated from a popu lation of vaccine strain 783-inoculated pigs.