Chamba Pardo Fabian Orlando, Alba-Casals Ana, Nerem Joel, Morrison Robert B, Puig Pedro, Torremorell Montserrat
Veterinary Population Medicine Department, University of Minnesota, St. Paul, MN, United States.
Pipestone Veterinary Services, Pipestone, MN, United States.
Front Vet Sci. 2017 Oct 11;4:167. doi: 10.3389/fvets.2017.00167. eCollection 2017.
Influenza is a costly disease for pig producers and understanding its epidemiology is critical to control it. In this study, we aimed to estimate the herd-level prevalence and seasonality of influenza in breed-to-wean pig farms, evaluate the correlation between influenza herd-level prevalence and meteorological conditions, and characterize influenza genetic diversity over time. A cohort of 34 breed-to-wean farms with monthly influenza status obtained over a 5-year period in piglets prior to wean was selected. A farm was considered positive in a given month if at least one oral fluid tested influenza positive by reverse transcriptase polymerase chain reaction. Influenza seasonality was assessed combining autoregressive integrated moving average (ARIMA) models with trigonometric functions as covariates. Meteorological conditions were gathered from local land-based weather stations, monthly aggregated and correlated with influenza herd-level prevalence. Influenza herd-level prevalence had a median of 28% with a range from 7 to 57% and followed a cyclical pattern with levels increasing during fall, peaking in both early winter (December) and late spring (May), and decreasing in summer. Influenza herd-level prevalence was correlated with mean outdoor air absolute humidity (AH) and temperature. Influenza genetic diversity was substantial over time with influenza isolates belonging to 10 distinct clades from which H1 delta 1 and H1 gamma 1 were the most common. Twenty-one percent of farms had three different clades co-circulating over time, 18% of farms had two clades, and 41% of farms had one clade. In summary, our study showed that influenza had a cyclical pattern explained in part by air AH and temperature changes over time, and highlighted the importance of active surveillance to identify high-risk periods when strategic control measures for influenza could be implemented.
流感对养猪生产者来说是一种代价高昂的疾病，了解其流行病学对于控制该疾病至关重要。在本研究中，我们旨在估计种猪到断奶仔猪养殖场中流感的群体水平流行率和季节性，评估流感群体水平流行率与气象条件之间的相关性，并随时间推移对流感的遗传多样性进行特征描述。我们选择了一组34个种猪到断奶仔猪养殖场，这些养殖场在5年期间每月都有断奶前仔猪的流感状况数据。如果至少一份口腔液体经逆转录酶聚合酶链反应检测为流感阳性，则该养殖场在给定月份被视为阳性。我们结合自回归积分移动平均（ARIMA）模型和三角函数作为协变量来评估流感的季节性。气象条件从当地地面气象站收集，按月汇总并与流感群体水平流行率相关联。流感群体水平流行率的中位数为28%，范围为7%至57%，呈周期性模式，秋季水平上升，初冬（12月）和晚春（5月）达到峰值，夏季下降。流感群体水平流行率与室外平均空气绝对湿度（AH）和温度相关。随着时间的推移，流感的遗传多样性很大，流感分离株属于10个不同的进化枝，其中H1δ1和H1γ1最为常见。21%的养殖场随着时间的推移有三种不同的进化枝共同流行，18%的养殖场有两种进化枝，41%的养殖场有一个进化枝。总之，我们的研究表明，流感呈周期性模式，部分原因是空气AH和温度随时间变化，并且强调了主动监测对于识别可实施流感战略控制措施的高危时期的重要性。
