Swine Disease Eradication Center, University of Minnesota, College of Veterinary Medicine, 385C Animal Science Veterinary Medicine Building, 1988 Fitch Avenue, St. Paul, MN 55108, USA.
Vaccine. 2012 Jan 5;30(2):407-13. doi: 10.1016/j.vaccine.2011.10.075. Epub 2011 Nov 7.
There are ongoing efforts to eliminate porcine reproductive and respiratory syndrome virus (PRRSv) from regions in the United States swine industry. However, an important challenge for the accomplishment of those efforts is the re-infection of pig units due to the area spread of PRRSv. The objective of this study was to evaluate the effect of PRRS modified-live virus vaccine (MLV) on viral shedding and on dynamics of PRRSv infection in pig populations raised under commercial conditions. The study composed of two rooms of 1000 pigs each. Ten percent of pigs of each room were inoculated with a field isolate of PRRSv. Rooms had separate air spaces and strict scientifically validated biosecurity protocols were adopted to avoid movement of pathogens between rooms. At 8 and 36 dpi (days post inoculation), all pigs of the challenge-vaccine group were inoculated with a MLV vaccine. Pigs of the challenge-control group were placebo-inoculated. Blood and oral fluid samples were collected from each room at 0, 8, 36, 70, 96 and 118 dpi for PRRSv RNA detection using PCR. PRRSv-antibodies were also screened from blood serum samples with a commercially available ELISA test. Additionally, tonsil scraping samples were collected from both groups at 70, 96 and 118 dpi. Moreover, air samples were collected 6 times per week from 0 to 118 dpi and were tested for PRRSv RNA using qPCR assay. There was no difference in the PRRSv infection dynamics measured as duration and magnitude of viremia and seroconversion. Also, there was no difference in the frequency of tonsil scraping samples PRRSv-positive by PCR. However, the challenge-vaccine group had significantly less PRRSv shed compared to the challenge-control group. The challenge-vaccine group had significant less PRRSv-positive oral fluids at 36 dpi. Moreover, the challenge-vaccine group had significant reduction in the cumulative PRRSv shed in the air.
目前，美国养猪业正在努力清除猪繁殖与呼吸综合征病毒（PRRSv）。然而，由于 PRRSv 在该地区的传播，这些努力的一个重要挑战是猪群的再次感染。本研究的目的是评估 PRRS 减毒活疫苗（MLV）对商业条件下饲养的猪群中病毒脱落和 PRRSv 感染动力学的影响。该研究由两个各有 1000 头猪的房间组成。每个房间的 10%的猪接种了 PRRSv 的田间分离株。两个房间有独立的空气空间，并采用严格科学验证的生物安全协议，以避免病原体在房间之间传播。在接种后 8 天和 36 天（dpi），接种疫苗组的所有猪都接种了 MLV 疫苗。接种对照组的猪进行安慰剂接种。在 0、8、36、70、96 和 118 dpi 时，从每个房间采集血液和口腔液样本，使用 PCR 检测 PRRSv RNA。使用商业上可用的 ELISA 试验从血清样本中筛选 PRRSv 抗体。此外，在 70、96 和 118 dpi 时，从两组猪中采集扁桃体刮取样本。此外，从 0 天到 118 天，每周采集 6 次空气样本，使用 qPCR 检测 PRRSv RNA。病毒血症和血清转化的持续时间和幅度等 PRRSv 感染动力学没有差异。PCR 检测扁桃体刮取样本 PRRSv 阳性的频率也没有差异。然而，接种疫苗组的 PRRSv 脱落量明显少于接种对照组。接种疫苗组在 36 dpi 时口腔液中 PRRSv 阳性的比例显著较低。此外，接种疫苗组空气中累积的 PRRSv 脱落量显著减少。
