Food and Veterinary Service, Riga, Latvia.
Institute of Food Safety, Animal Health and Environment-'BIOR', Riga, Latvia.
Transbound Emerg Dis. 2020 Nov;67(6):2615-2629. doi: 10.1111/tbed.13611. Epub 2020 May 31.
In 2014, African swine fever (ASF) emerged in Latvia for the first time. The majority of cases appeared in wild boar, but the presence of ASF in these animals constitutes a permanent threat to domestic pig holdings. Recent studies have shown an increase in serologically positive and a decrease in PCR-positive ASF cases in wild boar, possibly indicating a decline of ASF incidence. We aimed to investigate the course of the ASF epidemic in wild boar in Latvia, thus attaining further insights into the ASF epidemiology in this country with the goal of assessing the stage of the epidemic. Latvian ASF surveillance data of wild boar were utilized to estimate the seroprevalence and ASF virus (ASFV) prevalence in the wild boar population. Prevalence estimates were obtained for both the eastern and western part of the country and in addition for the 2014/2015 to 2018/2019 hunting seasons. Moreover, prevalence estimates for three different age classes were calculated. An increase in serologically positive yet PCR-negative wild boar samples from active surveillance was identified over time. When comparing the age groups, wild boar younger than one year displayed the ASFV prevalence to be higher than the seroprevalence, whereas older animals shared higher seroprevalence estimates. These findings support the assumption that only a small proportion of affected animals survive an infection, leading to an accumulation of their numbers over time. As a result, ASF elimination in a country with an infected wild boar population could possibly be achieved, if effective wild boar population management and surveillance is maintained and combined with the detection and removal of wild boar carcasses to reduce the viral load in the environment. In addition, the wild boar population should be kept as small as possible to break the ASFV infection cycle.
2014 年，非洲猪瘟（ASF）首次在拉脱维亚出现。大多数病例出现在野猪中，但这些动物中存在 ASF 对国内养猪场构成了永久性威胁。最近的研究表明，野猪中血清学阳性病例增多，PCR 阳性 ASF 病例减少，这可能表明 ASF 发病率有所下降。我们旨在调查拉脱维亚野猪中 ASF 疫情的发展，从而进一步了解该国的 ASF 流行病学，目的是评估疫情阶段。我们利用拉脱维亚野猪 ASF 监测数据来估算野猪种群中的血清流行率和 ASF 病毒（ASFV）流行率。对该国东部和西部以及 2014/2015 至 2018/2019 狩猎季节进行了流行率估计。此外，还计算了三个不同年龄组的流行率估计值。随着时间的推移，从主动监测中发现血清学阳性但 PCR 阴性的野猪样本数量有所增加。在比较年龄组时，年龄小于一岁的野猪显示出比血清流行率更高的 ASFV 流行率，而年龄较大的动物则具有更高的血清流行率估计值。这些发现支持了一个假设，即只有一小部分受感染的动物能够存活下来，从而导致其数量随时间积累。因此，如果有效管理和监测野猪种群，并结合检测和清除野猪尸体以降低环境中的病毒载量，那么在感染野猪的国家中可能实现 ASF 的消除。此外，应尽可能减少野猪种群数量，以打破 ASFV 感染循环。
