Etiological and molecular genetic surveillance of scrapie in Mongolia

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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.