Analysis of the Immune Efficacy of Attenuated Live Vaccine in the Pig Herds Previously Infected with Wild-type Porcine Reproductive and Respiratory Syndrome Virus

To evaluate the immune efficacy of porcine reproductive and respiratory syndrome (PRRS) attenuated live vaccine,this study selected 4 litters from two small pig farms (two litters each farm) and vaccinated with porcine reproductive and respiratory syndrome virus (PRRSV) attenuated live vaccine.Sera were collected on different days post vaccination (dpv) to detect PRRSV nucleic acid by RT-PCR,and PRRSV antibody using two different ELISA Kits,i.e.N-ELISA and G-ELISA.The results showed that PRRSV nucleic acid were positive on 0 dpv until 30 dpv in piglets and also positive on 0 dpv in the corresponding sows.All piglets were negative for PRRSV antibody on 0 dpv,but were positive on 30 dpv until 150 dpv.The positive rates detected by N-ELISA Kit were higher than those of G-ELISA Kit on 30 and 60 dpv,but lower than those of G-ELISA Kit on 120 and 150 dpv.A total of 216 sera were detected respectively by two ELISA Kits and the coincidence rate of the results was 95.83%.The P value of χ² test was more than 0.05,showing there was no significant difference between the results of two Kits.The Kappa value was 0.87,showing there was strong consistence between them.The correlation coefficient was 0.605,showing there was significantly linear correlation between them.The results indicated that the wild-type PRRSV in the previously infected pig herds could be eliminated by vaccination with attenuated live vaccine and both N-ELISA and G-ELISA Kits could be used to estimate the immune efficacy of the attenuated live vaccine effectively.