Konold Timm, Spiropoulos John, Thorne Jemma, Phelan Laura, Fothergill Louise, Rajanayagam Brenda, Floyd Tobias, Vidana Beatriz, Charnley Judith, Coates Nadya, Simmons Marion
Pathology Department, Animal and Plant Health Agency Weybridge, Addlestone, United Kingdom.
Central Sequencing Unit, Animal and Plant Health Agency Weybridge, Addlestone, United Kingdom.
Front Bioeng Biotechnol. 2020 Mar 12;8:164. doi: 10.3389/fbioe.2020.00164. eCollection 2020.
Current European surveillance regulations for scrapie, a naturally occurring transmissible spongiform encephalopathy (TSE) or prion disease in sheep and goats, require testing of fallen stock or healthy slaughter animals, and outline measures in the case of confirmation of disease. An outbreak of classical scrapie in a herd with 2500 goats led to the culling of the whole herd, providing the opportunity to examine a subset of goats, take samples, and examine them for the presence of disease-associated prion protein (PrP) to provide further information on scrapie test sensitivity, pathology, and association with prion protein genotype. Goats were examined clinically prior to cull, and the brains examined post mortem by Bio-Rad ELISA, a rapid screening test used for active surveillance in sheep and goats, and two confirmatory tests, Western blot and immunohistochemistry. Furthermore, up to 10 lymphoid tissues were examined by immunohistochemistry. Of 151 goats examined, three (2.0%) tested positive for scrapie by ELISA on brain, confirmed by confirmatory tests, and a further five (3.3%) were negative by ELISA but positive by at least one of the confirmatory tests. Only two of these, both positive by ELISA, displayed evident signs of scrapie. In addition, 10 (6.6%) goats, which also included two clinical suspects, were negative on brain examination but had detectable PrP in lymphoid tissue. PrP was detected most frequently in the medial retropharyngeal lymph node (LN; 94.4% of all 18 cases) and palatine tonsil (88.9%). Abnormal behavior and circling or loss of balance when blindfolded were the best clinical discriminators for scrapie status. None of the goats that carried a single allele in the prion protein gene associated with increased resistance to scrapie (Q, K, S) were scrapie-positive, and the percentage of goats with these alleles was greater than expected from previous surveys. Significantly more goats that were scrapie-positive were isoleucine homozygous at codon 142 (II). The results indicate that the sensitivity of the applied screening test is poor in goats compared to the confirmatory tests as gold standard, particularly for asymptomatic animals. Sensitivity of surveillance could be improved by testing retropharyngeal LN or palatine tonsil in addition to brain.
当前欧洲针对羊瘙痒病（一种绵羊和山羊自然发生的传染性海绵状脑病（TSE）或朊病毒病）的监测法规要求对死亡牲畜或健康屠宰动物进行检测，并概述了疾病确诊后的应对措施。一个拥有2500只山羊的羊群爆发了经典型羊瘙痒病，导致整个羊群被扑杀，这提供了一个机会来检查一部分山羊、采集样本，并检测样本中是否存在与疾病相关的朊病毒蛋白（PrP），以获取关于羊瘙痒病检测敏感性、病理学以及与朊病毒蛋白基因型关联的更多信息。在扑杀前对山羊进行临床检查，扑杀后对大脑进行检测，采用伯乐酶联免疫吸附测定法（Bio-Rad ELISA）（一种用于绵羊和山羊主动监测的快速筛查检测方法）以及两种确证检测方法——蛋白质印迹法和免疫组织化学法。此外，对多达10个淋巴组织进行免疫组织化学检测。在接受检测的151只山羊中，有3只（2.0%）大脑经酶联免疫吸附测定法检测为羊瘙痒病阳性，经确证检测得以确认；另有5只（3.3%）酶联免疫吸附测定法检测为阴性，但至少经一种确证检测为阳性。其中只有2只经酶联免疫吸附测定法检测为阳性的山羊表现出明显的羊瘙痒病症状。此外，有10只（6.6%）山羊，其中还包括2只临床疑似病例，大脑检测为阴性，但在淋巴组织中检测到了可检测到的PrP。PrP最常在咽后内侧淋巴结（LN；在所有18例病例中占94.4%）和腭扁桃体（88.9%）中检测到。异常行为以及蒙眼时转圈或失去平衡是区分羊瘙痒病状态的最佳临床指标。在朊病毒蛋白基因中携带与增强对羊瘙痒病抵抗力相关的单个等位基因（Q、K、S）的山羊均未检测为羊瘙痒病阳性，并且携带这些等位基因的山羊比例高于以往调查的预期。羊瘙痒病阳性的山羊中，密码子142处异亮氨酸纯合（II）的比例显著更高。结果表明，与作为金标准的确证检测相比，所应用的筛查检测在山羊中的敏感性较差，尤其是对于无症状动物。除大脑外，检测咽后淋巴结或腭扁桃体可提高监测的敏感性。
