Longitudinal Immune Response on PRRS in Vaccinated Pigs for 26 Weeks Period

The most economically important infectious disease in pig industry is Porcine Reproductive and Respiratory Syndrome (PRRS). Serological profiles of the PRRS using ELISA test is an important tool in monitoring and evaluating health status in farms. The dynamic of immune response on PRRS in a longitudinal fashion has not yet been studied in the real situation on farm in Thailand. The purpose of this study was to observe serological profiles on PRRS immune response, in pigs for 26 weeks period, in a longitudinal fashion.

A total of 126 blood samples were collected from 18 pigs in a self-replaced farm with history of PRRS-stabilized health status. The blood samples were longitudinally collected at 2, 6, 10, 14, 18, 22 and 26 weeks of age and assayed for ELISA using IDEXX PRRS X3 Ab Test (Idexx Laboratories, USA) as well as serum neutralizing (SN) titer. All pigs were vaccinated with MLV PRRS vaccine at 2 weeks of age.

The result from ELISA test was presented as mean of sample to positive ratio (S/P) ± standard deviation. The overall average S/P was 1.432 ± 0.905 (0.014-3.192). The average of S/P in each age group was 1.315±0.73, 1.028±0.64, 1.339±1.08, 1.788±1.02, 1.621±1.00, 1.472±0.92 and 1.461±0.81, respectively. For the SN titer was log2 transformed and shown as mean ± standard deviation. The overall average of the SN titer was 2.302±0.906 (range 1.77 -3.55). The averages of SN titer at 2, 6, 10, 14, 18, 22 and 26 weeks were 3.556±0.784, 1.833±0.786, 1.722 ±0.575, 1.778±0.808, 1.778 ±0.878, 2.556±1.381, and 2.889±1.132, respectively. The lowest SN titer was 1.722±0.575 at 10 weeks, which occur with neutralizing of maternal derived antibody and MLV vaccine. The highest was 3.556 ±0.786 at 2weeks form maternal derived antibody.

This was a preliminary study observing ELISA titer and SN titer for PRRS in pigs in a longitudinal fashion. This would represent the status of protective immunity in pigs to PRRS. All samples in this study were collected from a stable herd, thus, the ELISA S/P showed low variability. However, the maximum S/P was found at 14 weeks of age, the highest in average S/P, and decline after 18 weeks of age. The study also showed that SN in pigs that had vaccinated once at 2 weeks of age could maintain SN titer for a long period of time, at least 24 weeks after vaccination, in this study. This might answer some questions asked about the preparation of replacement gilts on farm to acclimatize for the PRRS to keep stability of health status of sow herds on vaccination program.

Disclosure of Interest: None Declared.