Hamir Amir N, Miller Janice M, O'Rourke Katherine I, Bartz Jason C, Stack Mick J, Chaplin Melanie J
National Animal Disease Center, ARS, USDA, 2300 Dayton Avenue, PO Box 70, Ames, IA 50010, USA.
J Vet Diagn Invest. 2004 Jan;16(1):57-63. doi: 10.1177/104063870401600110.
To determine the transmissibility of transmissible mink encephalopathy (TME) agent to raccoons and to provide information about clinical course, lesions, and suitability of currently used diagnostic procedures for detection of transmissible spongiform encephalopathies (TSEs) in raccoons, 4 raccoon kits were inoculated intracerebrally with a brain suspension from mink experimentally infected with TME. One uninoculated raccoon kit served as a control. All 4 animals in the TME-inoculated group showed clinical signs of neurologic disorder and were euthanized between 21 and 23 weeks postinoculation (PI). Necropsy examinations revealed no gross lesions. Spongiform encephalopathy was observed by light microscopy, and the presence of protease-resistant prion protein (PrPres) was detected by immunohistochemistry and Western blot techniques. Scrapie-associated fibrils were observed by negative-stain electron microscopy in the brains of 3 of the 4 inoculated raccoons. These findings confirm that TME is experimentally transmissible to raccoons and that diagnostic techniques currently used for TSE in livestock detect prion protein in raccoon tissue. According to previously published data, the incubation period of sheep scrapie in raccoons is 2 years, whereas chronic wasting disease (CWD) had not shown transmission after 3 years of observation. Because incubation periods for the 3 US TSEs (scrapie, TME, and CWD) in raccoons appear to be markedly different, it may be possible to use raccoons for differentiating unknown TSE agents. Retrospective genotyping of raccoons using frozen spleens showed that the raccoon PrP gene is identical to the mink gene at codons 179 and 224. Further studies, such as the incubation periods of bovine spongiform encephalopathy and other isolates of scrapie, CWD, and TME in raccoons, are needed before the model can be further characterized for differentiation of TSE agents.
为确定传染性水貂脑病（TME）病原体对浣熊的传染性，并提供有关临床病程、病变以及当前用于检测浣熊传染性海绵状脑病（TSE）的诊断程序适用性的信息，将4只浣熊幼崽脑内接种来自实验感染TME的水貂的脑悬液。1只未接种的浣熊幼崽作为对照。接种TME的组中的所有4只动物均表现出神经功能障碍的临床症状，并在接种后（PI）21至23周实施安乐死。尸检未发现肉眼可见的病变。通过光学显微镜观察到海绵状脑病，通过免疫组织化学和蛋白质印迹技术检测到抗蛋白酶朊病毒蛋白（PrPres）的存在。在4只接种浣熊中的3只的脑中，通过负染电子显微镜观察到瘙痒病相关纤维。这些发现证实TME可通过实验传染给浣熊，并且当前用于家畜TSE检测的诊断技术可检测浣熊组织中的朊病毒蛋白。根据先前发表的数据，绵羊瘙痒病在浣熊中的潜伏期为2年，而慢性消耗病（CWD）在观察3年后未显示传播。由于美国的3种TSE（瘙痒病、TME和CWD）在浣熊中的潜伏期似乎明显不同，因此有可能利用浣熊来区分未知的TSE病原体。使用冷冻脾脏对浣熊进行回顾性基因分型表明，浣熊PrP基因在密码子179和224处与水貂基因相同。在该模型可进一步用于区分TSE病原体之前，还需要进行进一步的研究，例如牛海绵状脑病以及瘙痒病、CWD和TME的其他分离株在浣熊中的潜伏期研究。
