Etiological and molecular genetic surveillance of scrapie in Mongolia

蒙古的养羊历史悠久，现在养着1200多万只羊。未来，蒙古有潜力成为世界上主要的畜产品供应国。因此，对蒙古动物中朊病毒疾病的监测将为评价该国畜产品的安全性提供重要信息。在研究期间，我们走访了蒙古中部、西部和东部地区，在听力上没有得到疑似羊瘙痒病存在的积极迹象。我们还检查了绵羊延髓中的PrPSc，显示神经症状，但所有的PrPSc均为阴性。为了研究蒙古绵羊PrP基因的多样性，我们采集了9个不同品种（Khalkh、Yeroo、Orkhon、Khangai、Sartuul、govis -altai、Bayad、Darhad和Symber-Karakul）共470份静脉血样本，并纯化了基因组DNA。通过对PrP开放阅读框对应的pcr扩增片段直接测序确定PrP基因型（氨基酸型）。关于决定痒病易感性的密码子171上的PrP基因型，携带与痒病易感性相关的171-Gln/Gln基因型的绵羊在不同品种之间的差异从58%到97%不等。携带171-Arg/Arg或171-Arg/Gln基因型的绵羊数量较少，特别是携带171-Arg等位基因纯合子的绵羊比例较小。这些结果表明，蒙古羊属于羊痒病易感人群，因此对感染朊病毒的动物采取持续监测和预防措施对评估朊病毒疾病的风险具有重要意义。这些结果也有助于进行选择性育种计划，以产生抗痒病的羊群。

Mongolia has a far long history for sheep-farming and is now farming over twelve million sheep. In the future, Mongolia has a potential for the major provider of livestock products among the world. Thus surveillance of prion diseases in animal in Mongolia will provide important information to evaluate the safety of livestock products in the country. During the research term, we visit to central, west, and east part of Mongolia, we did not get a positive indication on the existence of scrapie-suspected sheep in hearing. We also checked PrPSc in the medulla oblongata from sheep showed neurological symptoms, but all were negative for PrPSc.In order to investigate the diversity of PrP gene of sheep in Mongolia, we collected a total of 470 venous blood samples from 9 different breeds (Khalkh, Yeroo, Orkhon, Khangai, Sartuul, Govi-altai, Bayad, Darhad, and Symber-Karakul) and purified genomic DNA. PrP genotype (amino acid type) was determined by direct sequencing of PCR-amplified fragment corresponding to PrP open reading frame. With regard to PrP genotype at codon 171 determining susceptibility to scrapie, sheep carrying 171-Gln/Gln genotype that is associated with the susceptibility to scrape, varied from 58 to 97% among the breeds. Sheep carrying 171-Arg/Arg or 171-Arg/Gln genotype that confers resistance to scrapie infection were less abundant, especially only a small percentage of sheep possessed homozygous for 171-Arg alle. These results indicate sheep in Mongolia is composed rather of scrapie-susceptible population, so continuous surveillance as well as preventive measures against prion-infected animal are important to evaluate the risk of prion disease. These results are also useful for performing a selective breeding program that produce scrapie-resistant flock.