African swine fever (ASF) was first detected in the Estonian wild boar population in September 2014, while the first domestic pig farm was affected in July 2015. In the present study, we aimed to analyse, retrospectively, the epidemiology of the disease in all 26 outbreaks in domestic pig herds that occurred in Estonia during the period 2015-2017. Formal interviews were conducted to estimate the high-risk period for every farm, and to identify the possible origin of the ASF virus and the mode of virus introduction. Furthermore, the clinical manifestation of the disease as well as the course of the disease within the farm were investigated. Survival analysis was used to calculate herd incidence and to estimate outbreak risk. A hierarchical Bayesian space-time model was used to analyse the associations between outbreaks and ASF occurrence in wild boar. The spatial and temporal distribution of outbreaks was analysed to characterise the ASF epidemic in the Estonian domestic pig population from 2015 to 2017. The estimated high-risk period varied from seven to 20 days with a median of 11 days. On most of the affected farms, the first clinical signs were mild and not specific to ASF despite the high virulence of the circulating virus. Morbidity and mortality were often limited to a single pen or unit of the farm. The highest mortality (29.7%) was seen on backyard farms with 1-10 pigs and the lowest (0.7%) on large commercial farms (>1000 pigs). The spread of the virus within affected farms has been slow and the contagiousness of the virus has been relatively low. Farms of all sizes and types have been at risk, including large commercial farms operating at a high biosecurity level. In none of the affected farms could the specific route of introduction be verified. However, the findings suggested that virus introduction occurred via indirect transmission routes due to insufficient biosecurity. The total herd incidence of outbreaks was similar across all three years, being 2.4% in 2015 and 2016, and 2.0% in 2017. All outbreaks occurred from June to September, during the warmest period of the year. The results suggest that the increase in ASF cases in local wild boar populations is the main risk factor leading to the infection of farms; 88% of outbreaks occurred in areas where ASF virus was detected in wild boar prior to the outbreak, within a radius of 15 km from the outbreak farm.

中文翻译：

---

爱沙尼亚2015-2017年非洲猪瘟疫情的流行病学分析。

2014年9月，在爱沙尼亚野猪种群中首次发现非洲猪瘟（ASF），而2015年7月，第一个家养猪场受到了感染。在本研究中，我们旨在回顾性分析该疾病的流行病学2015-2017年期间，爱沙尼亚发生了26起家养猪群暴发。进行了正式访谈，以估计每个农场的高风险期，并确定ASF病毒的可能来源和病毒引入方式。此外，还研究了该疾病的临床表现以及农场内的疾病进程。生存分析用于计算牛群的发病率和估计暴发风险。使用分级贝叶斯时空模型分析野猪中暴发与ASF发生之间的关联。分析了疫情的时空分布，以表征爱沙尼亚2015年至2017年家猪种群中的ASF流行病。估计的高危期从7天到20天不等，中位数为11天。在大多数受影响的农场中，尽管正在传播的病毒具有高毒力，但最初的临床体征是轻度的，并不是针对ASF的。发病率和死亡率通常仅限于农场的单个围栏或单位。在1-10头猪的后院农场中，死亡率最高（29.7％），而在大型商业农场（> 1000头猪）中，死亡率最低（0.7％）。病毒在受影响的农场中的传播缓慢，病毒的传染性相对较低。各种规模和类型的农场都处于危险之中，包括具有高生物安全水平的大型商业农场。在所有受影响的农场中，都无法验证具体的引入途径。但是，研究结果表明，由于生物安全性不足，病毒是通过间接传播途径引入的。在这三年中，牛群的总体暴发率相似，在2015年和2016年为2.4％，在2017年为2.0％。所有暴发发生在当年最热的6月至9月。结果表明，当地野猪种群中ASF病例的增加是导致农场感染的主要危险因素。88％的暴发发生在爆发前野猪在距离爆发农场15公里半径内的野猪中检测到ASF病毒的地区。