White L A, Torremorell M, Craft M E
Department of Ecology, Evolution & Behavior, University of Minnesota, 140 Gortner Laboratory, 1479 Gortner Avenue, St. Paul, MN 55108, USA.
Department of Veterinary Population Medicine, University of Minnesota, 385 Animal Science/Veterinary Medicine Building, 1988 Fitch Avenue, St. Paul, MN 55108, USA.
Prev Vet Med. 2017 Mar 1;138:55-69. doi: 10.1016/j.prevetmed.2016.12.013. Epub 2016 Dec 24.
Recent modelling and empirical work on influenza A virus (IAV) suggests that piglets play an important role as an endemic reservoir. The objective of this study is to test intervention strategies aimed at reducing the incidence of IAV in piglets and ideally, preventing piglets from becoming exposed in the first place. These interventions include biosecurity measures, vaccination, and management options that swine producers may employ individually or jointly to control IAV in their herds. We have developed a stochastic Susceptible-Exposed-Infectious-Recovered-Vaccinated (SEIRV) model that reflects the spatial organization of a standard breeding herd and accounts for the different production classes of pigs therein. Notably, this model allows for loss of immunity for vaccinated and recovered animals, and for vaccinated animals to have different latency and infectious periods from unvaccinated animals as suggested by the literature. The interventions tested include: (1) varied timing of gilt introductions to the breeding herd, (2) gilt separation (no indirect transmission to or from the gilt development unit), (3) gilt vaccination upon arrival to the farm, (4) early weaning, and (5) vaccination strategies of sows with different timing (mass and pre-farrow) and efficacy (homologous vs. heterologous). We conducted a Latin Hypercube Sampling and Partial Rank Correlation Coefficient (LHS-PRCC) analysis combined with a random forest analysis to assess the relative importance of each epidemiological parameter in determining epidemic outcomes. In concert, mass vaccination, early weaning of piglets (removal 0-7days after birth), gilt separation, gilt vaccination, and longer periods between introductions of gilts (6 months) were the most effective at reducing prevalence. Endemic prevalence overall was reduced by 51% relative to the null case; endemic prevalence in piglets was reduced by 74%; and IAV was eliminated completely from the herd in 23% of all simulations. Importantly, elimination of IAV was most likely to occur within the first few days of an epidemic. The latency period, infectious period, duration of immunity, and transmission rate for piglets with maternal immunity had the highest correlation with three separate measures of IAV prevalence; therefore, these are parameters that warrant increased attention for obtaining empirical estimates. Our findings support other studies suggesting that piglets play a key role in maintaining IAV in breeding herds. We recommend biosecurity measures in combination with targeted homologous vaccination or vaccines that provide wider cross-protective immunity to prevent incursions of virus to the farm and subsequent establishment of an infected piglet reservoir.
最近关于甲型流感病毒（IAV）的建模和实证研究表明，仔猪作为地方病宿主发挥着重要作用。本研究的目的是测试旨在降低仔猪IAV发病率的干预策略，理想情况下，首先防止仔猪接触病毒。这些干预措施包括生物安全措施、疫苗接种以及养猪生产者可单独或联合采用的管理选项，以控制其猪群中的IAV。我们开发了一种随机易感-暴露-感染-康复-接种（SEIRV）模型，该模型反映了标准繁殖猪群的空间组织，并考虑了其中不同生产类别的猪。值得注意的是，该模型考虑了接种疫苗和康复动物的免疫力丧失，以及如文献所建议的，接种疫苗的动物与未接种疫苗的动物具有不同的潜伏期和感染期。测试的干预措施包括：（1）向繁殖猪群引入后备母猪的时间不同，（2）后备母猪隔离（与后备母猪培育单元无间接传播），（3）后备母猪到达农场后接种疫苗，（4）早期断奶，以及（5）不同时间（大规模和产前）和效力（同源与异源）的母猪疫苗接种策略。我们进行了拉丁超立方抽样和偏秩相关系数（LHS-PRCC）分析，并结合随机森林分析，以评估每个流行病学参数在确定疫情结果中的相对重要性。同时，大规模疫苗接种、仔猪早期断奶（出生后0 - 7天断奶）、后备母猪隔离、后备母猪疫苗接种以及后备母猪引入间隔时间延长（6个月）在降低患病率方面最为有效。总体地方病患病率相对于空模型情况降低了51%；仔猪的地方病患病率降低了74%；在所有模拟中，23%的猪群中IAV被完全消除。重要的是，IAV最有可能在疫情的头几天内被消除。具有母源免疫力的仔猪的潜伏期、感染期、免疫持续时间和传播率与IAV患病率的三个单独指标具有最高的相关性；因此，这些参数值得更多关注以获得实证估计。我们的研究结果支持其他研究，表明仔猪在繁殖猪群中维持IAV方面起着关键作用。我们建议将生物安全措施与针对性的同源疫苗接种或提供更广泛交叉保护免疫力的疫苗相结合，以防止病毒侵入农场并随后建立感染仔猪宿主。
