Transmission of two pseudorabies virus strains that differ in virulence and 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-inoculated pigs.

DESIGN

Three experiments were conducted, each with 2 groups of 10 pigs inoculated with the glycoprotein E-negative vaccine 783. In the first 2 experiments, half of one group was inoculated with the mildly virulent strain Sterksel, and half of the other group was inoculated with the virulent strain NIA-3. The remaining pigs were contact-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 contact-exposed to these 2 pigs.

ANIMALS

Specific-pathogen-free pigs that were sero-negative for antibodies to PRV.

PROCEDURE

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 reproduction ratio theta. A glycoprotein E ELISA was used to determine whether infection occurred. Virus excretion in the oropharyngeal fluid was determined by plaque assay to measure infectivity.

RESULTS

Vaccinated pigs had a significant difference in virus excretion between the mildly virulent and virulent strains. Sterksel strain-inoculated pigs shed significantly more virus than did NIA-3 strain-inoculated pigs. Despite this difference in virus excretion, the 2 strains did not differ in transmission.

CONCLUSIONS

Both PRV strains would be eliminated from a population of vaccine strain 783-inoculated pigs.