Some farms where NA type MLV had been used for a long time, decided to change their vaccine to EU type MLV. After 1- 2 month since they started EU type MLV, they did antibody monitoring by using ELISA. Through this sero-monitoring, we can see the negative or variable level of antibody titer in the whole pig group. Are these ELISA results meaningful to understand vaccine efficacy in each farm?
Administration of the PRRSV vaccine in pigs will induce specific antibodies to corresponding viral proteins. Those antibodies can be detected by several serological tests. ELISA is one of the most common test to detect the PRRSV antibodies. Vaccination will increase the rate of antibody positive and its titer in vaccinated pigs but repetitive vaccination will not increase further the antibody titer.
Several ELISA kits are available for the PRRSV antibody detection and results are variable depending on the commercial kits. Animals vaccinated with PRRSV usually show seroconversion by 21 days post vaccination by ELISA test. Some of the specific kits are developed for the type 1 PRRS virus. IDEXX PRRS X3 Ab Test will detect antibodies to type 1 PRRSV, based on the manufacturer’s test result release.
Animals vaccinated with MLV vaccine would have a tendency of low or variable level of antibody titers because of the previous exposure to field strains. Therefore, titers in sow and young piglets are not reliable to evaluate vaccination efficacy.
Animals vaccinated with safe MLV vaccine may have the tendency of low or variable levels of antibody titers because of the limited replication efficiency compared to field strains of PRRSV.
Therefore, in field conditions, antibody titers should not be a sole parameter for the estimation of vaccine efficacy.
Humoral immunity is an important indicator to evaluate efficiency of the vaccine and cellular immunity is more critical to eliminate virus from the host. I do recommend to use proper test kit and RT-PCR for the detection of the virus from serum sample to ensure efficacy of the vaccination.
University of Konkuk, South Korea