Abstract
Vaccination is currently the most effective strategy to control porcine reproductive and respiratory syndrome (PRRS). New-generation PRRS vaccines are required to be safe and broadly cross-protective. We have recently created the chimeric PRRS virus K418DM which proved to be a good vaccine candidate under field conditions. In the present study, we designed safety and efficacy tests under experimental and field conditions for further evaluation of K418DM1.1, a plaque-purified K418DM. In the homologous challenge study, K418DM1.1 induced high serum virus neutralization (SVN) antibody titers (i.e., 4.2 log2 ± 1.7) at 21 days post-challenge (dpc) and provided protection as demonstrated by the significantly lower levels of viremia at 3 and 7 dpc and significantly lower microscopic lung lesion scores compared to the unvaccinated group. K418DM1.1 was also protective in the heterologous challenge study, with vaccinated pigs showing significantly lower levels of viremia at 14 dpc compared to the unvaccinated pigs. A field study was performed to evaluate the efficacy of K418DM1.1 against heterologous exposure and vaccinated pigs presented significantly lower viremia than unvaccinated pigs. According to the safety test for the examination of virulence reversion, no infectivity was observed in tissue homogenate filtrate both in the vaccinated and comingled groups. Thus, the risk of virulence, as well as transmission, appeared negligible. These overall results indicate that K418DM1.1 is a good vaccine candidate based on its safety and protective efficacy.