Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St. Paul, MN, USA.
Transbound Emerg Dis. 2022 Mar;69(2):524-537. doi: 10.1111/tbed.14016. Epub 2021 Feb 21.
Swine production in the United States is characterized by dynamic farm contacts through animal movements; such movements shape the risk of disease occurrence on farms. Pig movements have been linked to the spread of a virulent porcine reproductive and respiratory syndrome virus (PRRSV), RFLP type 1-7-4, herein denoted as phylogenetic sub-lineage 1A [L1A]. This study aimed to quantify the contribution of pig movements to the risk of L1A occurrence on farms in the United States. Farms were defined as L1A-positive in a given 6-month period if at least one L1A sequence was recovered from the farm. Temporal network autocorrelation modelling was performed using data on animal movements and 1,761 PRRSV ORF5 sequences linked to 494 farms from a dense pig production area in the United States between 2014 and 2017. A farm's current and past exposure to L1A and other PRRSV variants was assessed through its primary and secondary contacts in the animal movement network. Primary and secondary contacts with an L1A-positive farm increased the likelihood of L1A occurrence on a farm by 19% (p = .04) and 23% (p = .03), respectively. While the risk posed by primary contacts with PRRS-positive farms is unsurprising, the observation that secondary contacts also increase the likelihood of infection is novel. Risk of L1A occurrence on a farm also increased by 3.0% (p = .01) for every additional outgoing shipment, possibly due to biosecurity breaches during loading and transporting pigs from the farm. Finally, use of vaccines or field virus inoculation on sow farms one year prior reduced the risk of L1A occurrence in downstream farms by 36% (p = .04), suggesting that control measures that reduce viral circulation and enhance immunological protection in sow farms have a carry-over effect on L1A occurrence in downstream farms. Therefore, coordinated disease management interventions between farms connected via animal movements may be more effective than individual farm-based interventions.
美国的生猪生产以农场间频繁的动物调运为特征，这种调运方式塑造了农场疫病发生的风险。猪的调运与一种强毒猪繁殖与呼吸综合征病毒（PRRSV）、RFLP 类型 1-7-4 的传播有关，本文将其命名为系统进化亚系 1A[L1A]。本研究旨在量化美国生猪生产中猪的调运对农场 L1A 发生风险的贡献。如果在特定的 6 个月内，从一个农场至少获得一个 L1A 序列，则将该农场定义为 L1A 阳性。使用 2014 年至 2017 年间美国一个密集的养猪生产区的动物调运数据和 1761 个与 494 个农场相关的 PRRSV ORF5 序列，对时间网络自相关模型进行了分析。通过动物调运网络中农场的主要和次要接触，评估农场当前和过去对 L1A 和其他 PRRSV 变体的暴露情况。与 L1A 阳性农场的主要和次要接触，使农场发生 L1A 的可能性分别增加了 19%（p=0.04）和 23%（p=0.03）。虽然与 PRRS 阳性农场的主要接触带来的风险并不出人意料，但次要接触也增加感染可能性的观察结果是新颖的。农场发生 L1A 的风险也会随着每增加一次出栏而增加 3.0%（p=0.01），这可能是由于在装载和运输猪的过程中出现了生物安全漏洞。最后，在一年前对母猪场使用疫苗或田间病毒接种，可使下游农场发生 L1A 的风险降低 36%（p=0.04），这表明减少母猪场病毒循环和增强免疫保护的控制措施，对下游农场 L1A 的发生具有延续效应。因此，通过动物调运相互联系的农场之间开展协调一致的疾病管理干预措施，可能比单个农场的干预措施更有效。
