Efficacy test of novel PRRSV live vaccine candidate in pigs

The purpose of this study was to evaluate immunogenicity of WGV1014 (KCTC 12784BP) by analyzing PRRSV-specific Ab titer and VN titer after challenge.

Animal. A total of 12 pigs, 3 weeks of age from a pig farm were used in the study. All pigs were confirmed to be free of PRRSV infections by use of IDEXX PRRSV X3 and VeTekTM PRRSV Detection kit. All groups of pigs were inoculated by IM route. Group 1 (n=3), 2 (n=3) and 3 (n=3) were inoculated with 10^4.5 TCID₅₀, 10^5.5 TCID₅₀ and 10^6.5 TCID₅₀ of strain WG1014, respectively. Group 4 (n=3) was injected with PBS as controls. All of 4 groups were inoculated 1 time. At day 35 after vaccination, all the animals were challenged intranasally with 10^4.5 TCID₅₀ field isolated PRRSV. Blood was taken on 0, 7, 14, 21, 28, 35, 42 and 49 days after vaccination and oral fluid samples were taken on 0, 1, 2, 3, 7, 14, 21, 28, 35, 42 and 49 days after vaccination. Serum and oral fluid samples were collected and stored at -70℃ before testing with ELISA and VN assay.

Enzyme-linked immunosorbent assay. The ELISA was performed using a IDEXX PRRS X3 as directed by the manufacturer. Serum samples were diluted 1:40 in a sample diluent. OD of each well was measured at 655 nm using a microplate reader. The presence or absence of antibody to PRRS was determined by calculating the sample to S/P ratio. Samples were considered to be positive for PRRS virus an antibody if S/P ratio > 0.4.

PRRSV VN titer assay. VN titers were determined by SN test on MARC-145 cells. A 2-fold diluted serum sample was prepared, and an equal volume of virus solution with a titer of 200 TCID50/mL was added to each dilution and incubated for 1 h at 37°C. The CPEs on the cells were analyzed for 7 days after inoculation. The VN antibody titer was defined as the reciprocal of the highest dilution that inhibited CPE in 50% of the inoculated wells.

SN titer of each vaccine group was depending on concentration. After challenge, S/P ratio and neutralizing antibody titers in vaccinated animals were significantly higher to protect PRRSV infection.

The novel PRRSV vaccine candidate raised enough S/P ration and SN titer to prevent PRRSV infection.

Disclosure of Interest: None Declared.