COMPARISON OF 2 PSEUDORABIES VIRUS-VACCINES, THAT DIFFER IN CAPACITY TO REDUCE VIRUS EXCRETION AFTER A CHALLENGE INFECTION, IN THEIR CAPACITY OF REDUCING TRANSMISSION OF PSEUDORABIES VIRUS

Pseudorabies virus (PRV) vaccines are often compared for their capacit y to reduce virus excretion after a challenge infection. Vaccines, use d for the eradication of PRV, however, should reduce transmission of P RV among pigs. The purpose of this study was to investigate whether th e amount of virus excreted after a challenge infection is an accurate measure of the capacity of a vaccine to reduce transmission of PRV amo ng pigs. Two experiments were carried out, each using two groups of 10 pigs. The pigs in group one were intramuscularly vaccinated once with the glycoprotein E (gE)-negative vaccine X, the pigs in group two wit h the gE-negative strain 783. Eight weeks later, 5 pigs in each group were inoculated with wild-type PRV. A gE-ELISA was used to detect PRV infection. The transmission of PRV was estimated from the number of co ntact infections and expressed as the reproduction ratio R. The inocul ated pigs vaccinated with vaccine X shed significantly more virus than the inoculated pigs vaccinated with strain 783. However, despite the difference in virus excretion, the transmission of PRV between the two groups did not differ. We conclude that virus excretion is not an acc urate measure for determining vaccine effectiveness. However, R of vac cine X (R = 0.98) was not significantly below one, whereas R of vaccin e 783 (R = 0) was significantly below one. Consequently, we cannot exc lude the possibility that major outbreaks of PRV occur among pigs vacc inated with vaccine X.