A modified-live porcine reproductive and respiratory syndrome virus (PRRSV)-1 vaccine protects late-term pregnancy gilts against heterologous PRRSV-1 but not PRRSV-2 challenge

The objective of this study was to determine the efficacy of a commercially available porcine reproductive and respiratory syndrome virus (PRRSV)-1 modified-live virus (MLV) vaccine against PRRSV-1 and PRRSV-2 challenge in late-term pregnancy gilts. Gilts were vaccinated with the PRRSV-1 MLV vaccine at 4 weeks prior to breeding and then challenged intranasally with PRRSV-1 or PRRSV-2 at 93 days of gestation. After PRRSV-1 challenge, vaccinated pregnant gilts had a significantly longer gestation period, significantly higher numbers of live-born and weaned piglets and a significantly lower number of stillborn piglets at birth compared to unvaccinated pregnant gilts. No significant improvement in reproductive performance was observed between vaccinated and unvaccinated pregnant gilts following PRRSV-2 challenge. Vaccinated pregnant gilts also exhibited a significantly improved reproductive performance after challenge with PRRSV-1 compared to vaccinated pregnant gilts following PRRSV-2 challenge. The PRRSV-1 MLV vaccine was able to reduce PRRSV-1 but not PRRSV-2 viremia in pregnant gilts. Vaccinated gilts also showed a significantly higher number of PRRSV-1-specific IFN-γ-secreting cells (IFN-γ-SC) compared to PRRSV-2-specific IFN-γ-SC. The data presented here suggest that the vaccination of pregnant gilts with a PRRSV-1 MLV vaccine provides good protection against PRRSV-1 but only limited protection against PRRSV-2 challenge in late-term pregnancy gilts based on improvement of reproductive performance, reduction in viremia and induction of IFN-γ-SC.