Abstract:
The humoral antibody responses following vaccination with different lineage of modified live genotype 2 porcine reproductive and respiratory syndrome virus (PRRSV) vaccines (MLVs) were investigated. Moreover, the mortality and growth performance in pigs were observed. Twenty-four pigs with high maternally derived antibody (MDA) levels (SN titer ≥ 8) from each PRRSV positive Herd 1 and Herd 2 were allocated to the H1, H1-1, and H1-2 groups (Herd 1) and H2, H2-1, and H2-2 groups (Herd 2). Twenty-four pigs with low MDA levels (SN titer <8) were allocated to the L1, L1-1, and L1-2 (Herd 1) and L2, L2-1, and L2-2 groups (Herd 2). Twenty-four pigs from the negative herd (Herd 3) were allocated to 3 groups: N, N-1, and N-2 groups. The H1, H2, L1, L2, and N groups were unvaccinated. The H1-1, H2-1, L1-1, L2-1, and N-1 groups were vaccinated with MLV (Ingelvac® PRRS MLV) at 2 weeks of age. The 5 other groups: H1-2, H2-2, L1-2, L2-2, and N-2 groups were vaccinated with MLV2 (Prime Pac® PRRS MLV) at 2 week of age. The antibody responses were measured by ELISA and serum neutralization (SN). The mortality was not observed in all vaccinated groups. Additionally, pigs with high MDA levels from the H1 and H2 groups did not exhibit the mortality throughout the study. ADG in pigs vaccinated with each MLV1 and MLV2 was significant higher than that in unvaccinated pigs. However, pigs vaccinated with MLV2 showed the highest values of ADG. Seroconversion was observed in all vaccinated groups with no significance difference in antibody titers between pigs with low and high MDA levels. However, pigs with low MDA levels showed the earliest and highest antibody level post vaccination. The highest SN-titer against MLV1 isolate and MLV2 isolate was observed in pig from the L1-1 and L2-2 groups, respectively. The field PRRSV-2 isolates: THA_SP/RB_S1/P1/0120-18 and THA_WC/RB_F165/20-22, the SN titers against these isolates were not observed in vaccinated groups. These results indicated that MDAs might not affect the immune response post vaccination. PRRSV-2 MLVs reduced the mortality and improved growth performance of pigs in the endemically PRRSV infected herds. Although, the vaccine was changed in weaning pigs, the antibody responses were detected post vaccination in both pigs with low and high level of MDAs. Moreover, the genetic similarity between vaccine and field virus was not related to the protection. Vaccine selection should depend on the induction of immune response and protection against heterologous PRRSV infection.
