Department of Microbiology, National Veterinary Institute, 75189, Uppsala, Sweden.
Department of Disease Control and Epidemiology, National Veterinary Institute, 75189, Uppsala, Sweden.
Acta Vet Scand. 2021 Apr 7;63(1):16. doi: 10.1186/s13028-021-00580-4.
The vector-borne human viral zoonosis tick-borne encephalitis (TBE) is of growing concern in Sweden. The area where TBE is considered endemic has expanded, with an increasing geographical distribution of Ixodes ricinus as the tick vector and a rising number of reported TBE cases in humans. Efforts to map TBE risk areas have been carried out by sentinel monitoring, mainly based on individual sampling and analysis of wild and domestic animals, as well as ticks, for tick-borne encephalitis virus (TBEV). However, the interpretation of the geographical distribution has been hampered by the patchy and focal nature of TBEV occurrence. This study presents TBEV surveillance data based on antibody analysis of bulk tank milk collected from dairy herds located throughout Sweden before (May) and after (November) the vector season. A commercial TBEV antibody ELISA was modified and evaluated for use in this study.
The initial comparative TBEV antibody analysis revealed a good correlation between milk and serum antibody levels from individually sampled cows. Also, the TBEV-antibody levels for the mean-herd serum showed good comparability with TBEV antibody levels from bulk tank milk, thus indicating good predictability of seroprevalence when analysing bulk tank milk from a herd. Analyses of bulk tank milk samples collected from 616 herds in May and 560 herds in November showed a geographical distribution of TBEV seropositive herds that was largely consistent with reported human TBE cases. A few TBEV-reactive herds were also found outside known locations of human TBE cases.
Serological examination of bulk tank milk from dairy cattle herds may be a useful sentinel surveillance method to identify geographical presence of TBEV. In contrast to individual sampling this method allows a large number of animals to be monitored. TBEV seropositive herds were mainly found in coastal areas of southern Sweden similar to human TBE cases. However, some antibody-reactive herds were found outside known TBE areas at the time of the study.
由媒介传播的人病毒性人畜共患病蜱传脑炎（TBE）在瑞典受到越来越多的关注。被认为是地方性疾病的地区范围已经扩大，由于媒介蜱壁虱属蓖麻硬蜱的地理分布不断增加，以及人类报告的 TBE 病例数量不断增加。已经通过哨点监测来努力绘制 TBE 风险区域图，主要是基于对野生动物和家畜以及壁虱属蓖麻硬蜱进行的病毒分析。然而，由于 TBEV 发生的局灶性和斑块性，对地理分布的解释受到了阻碍。本研究根据在媒介季节前后（5 月和 11 月）从瑞典各地奶牛场采集的批量牛奶进行的抗体分析，提供了 TBEV 监测数据。对一种商业 TBEV 抗体 ELISA 进行了修改并用于本研究。
最初的比较 TBEV 抗体分析显示，从单独采样的奶牛获得的牛奶和血清抗体水平之间存在良好的相关性。此外，平均群体血清中的 TBEV 抗体水平与批量牛奶中的 TBEV 抗体水平具有良好的可比性，因此表明分析群体中批量牛奶的血清阳性率具有良好的预测性。对 616 个牛群 5 月采集的批量牛奶样本和 560 个牛群 11 月采集的批量牛奶样本进行分析，发现 TBEV 血清阳性牛群的地理分布与报告的人类 TBE 病例基本一致。在已知的人类 TBE 病例位置之外也发现了一些 TBEV 反应性牛群。
对奶牛场的批量牛奶进行血清学检查可能是一种有用的哨点监测方法，可用于识别 TBEV 的地理存在。与个体采样相比，该方法可以监测大量动物。TBEV 血清阳性牛群主要分布在瑞典南部沿海地区，与人类 TBE 病例相似。然而，在研究时，在已知的 TBE 区域之外也发现了一些抗体反应性牛群。
