Clinical Evaluation And Analysis On The Efficacy Of Highly Pathogenic PRRSV Attenuated Live Vaccine TJM-F92

Modified (attenuated) live virus (MLV) vaccines are widely used to control porcine reproductive and respiratory syndrome virus (PRRSV) infection in China, however, much attention has been paid to the clinically safety and efficacy of PRRSV MLV. In this study, clinical use, safety and efficacy of the MLV vaccine derived from the highly pathogenic PRRSV (HP-PRRSV) TJM-F92 were evaluated and analyzed in order to provide scientific basis for reasonable application of this vaccine in practice.Seven hundred and twenty pig farms in 24 provinces with the use of TJM-F92 vaccine were investigated through questionnaire during March to May of 2015, in order to obtain information on the safety of this vaccine for sow herds and efficacy for growing herds. The feedback information showed tnat the percentage of "good", "better" and "less" for its safety from 700 sow herds was 52.29%,40.5% and 7.14%, respectively. Massive vaccination with 3-4 times per year was performed by over 93% sow herds. As well, the feedback information from 634 growing herds showed that the percentage of "good", "better" and "less" was 29.96%,59.31%, and 10.73%, respectively. In addition, some factors such as productive system, vaccination program and geographical region of farms were found to be related to the effectiveness of its vaccination.The situation and strains of PRRSV infection on pig farms were analyzed in order to evaluate the efficiency of TJM-F92 vaccine clinically. One hundred and sixty-three samples from 56 pig farms in 15 provinces, which were confirmed to be PRRSV-positive by RT-PCR, were used to amplfy and sequence ORF3, ORF5 and NSP2 highly variant region during April 2014 to April 2016. The amplified 130 ORF3 sequences,139 ORF5 sequences and 113 NSP2 fragments belonged to genotype 2 of PRRSV, and could be divided into 5 subgroups. A novel subgroup of ORF3 and ORF5 genes were discovered. Most of ORF3, ORF5 and NSP2 were clsuted into the group of HP-PRRSV, and they shared 68.4%, 68.46% and 84.07% of the sequenced products, respectively. Meanwhile,12 patterns of deletion in NSP2 region were found. After comprehensive analysis of the 3 genes of all samples from all the pig farms, the complication of PRRSV infection in the pig farms was revealed, and 9 PRRSV subgroup strains and 18 infectious patterns of PRRSV stain were found in the pig farms. The frequency of emergence for HP-PRRSV, NADC30-like and VR-2332 strains was 66.07%,26.79%, and 8.93%, respectively. And pig farms infected with single one of the three PRRSV strains, such as HP-PRRSV, NADC30-like and VR-2332 like, shared with 53.5%, and the ration of farms infected with single HP-PRRSV strain was highest, with 41.07%. In addition, Pig farms infected undefined and two or three PRRSV strains shared with 45.64%, and HP-PRRSV and NADC30-like strains co-existed on some pig farms were observed with the ration of 12%.Thirty-five of 56 pig farms with different PRRSV strain infections where the vaccine was used were investigated to evaluate its effectiveness through questionnaire survey.13/35,13/35 and 9/35 of the pig farms showed significant, less and no efficiency, respectively. After further analysis, the difference in the efficacy on the pig farms infected with different patterns of PRRSV strain was revealed. And on the pig farms infected with single HP-PRRSV,50%,38.5% and 12.5% of pig farms showed significant, less and no efficiency for the vaccinated pig herds, respectively. No significant efficiency for the farms infected by NADC30-like strains was observed.A pig farm vaccinated with TJM-F92 vaccine was monitored to evaluate the long-term influence of the vaccine on the reproductive performance of sow herds and the health status of growing herds from July 2014 to December 2015. Farrowing rate, litter performance of the vaccinated sows in different pregnant period, and mortality of different growing phases, serum antibody and PRRSV strains circulating in nursery pig herds were assessed. On the one hand, no significant difference was found for litter performance and farrowing rate of sow herds between post-vaccination and pre-vaccination. And the difference of the effect on litter performance was revealed in sow herds vaccinated with the TJM-F92 vaccine during different pregnant periods, and the highest mummy per litter was observed for sow herds vaccinated during 0-30 days after pregnancy, and there was significant difference with sow herds vaccinated during any other pregnant periods. On the other hand, after vaccination, the performance of growing herds was significantly improved, and the survival rate in nursery and finishing phases was 96.97±1.48% and 97.50±0.61%, respectively. In addition, the performance of nursery pig herds was observed to be closely related to the infection time and strains of PRRSV. Overall, the vaccination with the TJM-F92 vaccine is helpful to decline the circulation and infection of HP-PRRSV on pig farms.In conclusion, the systematic assessment on the safety and efficacy of TJM-F92 was conducted clinically, and valuable scientific basis were provided for the rational use of the attenuated live vaccine of TJM-F92 in the pig industry.