TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES: THE ROLE OF GENETICS, STRAIN VARIATION, AND ENVIRONMENTAL CONTAMINATION IN DISEASE CONTROL
Location: Animal Diseases Research
Title: Scant PrP-Sc accumulation in the placentas of goats with naturally acquired scrapie
Submitted to: BioMed Central (BMC) Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2011
Publication Date: February 1, 2011
Citation: Orourke, K.I., Zhuang, D., Truscott, T.C., Yan, H., Schneider, D.A. 2011. Scant PrP-Sc accumulation in the placentas of goats with naturally acquired scrapie. BioMed Central (BMC) Veterinary Research. 7(1):7.
Interpretive Summary: Scrapie is a fatal brain disease of sheep and goats, apparently spread through contact with placentas, milk, or blood from infected dams. The disease associated with a tightly folded form of the prion protein, a normal constituent of many tissues of goats and sheep. The normal form of the protein, PrP-cellular, is readily degraded by enzymes but the abnormal form, PrP-scrapie or PrP-sc, is resistant to degradation in the laboratory and in the tissues of the infected animal. PrP-Sc is therefore a reliable marker for the disease. Relative resistance to scrapie in sheep is genetically controlled and small changes in the gene encoding the cellular prion protein protect adults and lambs from infection following exposure. In addition, PrP-Sc is detected in the placentas of infected sheep only if the fetus is genetically susceptible, so that placental exclusion of PrP-Sc in a fetus with a novel genotype is a useful method for assessing potentially resistant genotypes. The role of the placenta in scrapie transmission in goats is not well understood. Scrapie in goats in rare in the United States and until the introduction of live animal testing, there were no reliable methods for investigating the role of the placenta in naturally infected goats. Although scrapie is readily transmitted experimentally to goats, there are no data on the accumulation of PrP-Sc infected goats and very little information on the placenta in infected sheep. In this study, we evaluated the placentas of naturally infected goats and sheep for PrP-Sc deposits. Although experimentally infected sheep and goats showed similar patterns of placental PrP-Sc accumulation, the placentas of naturally infected goats showed only sparse PrP-Sc deposits. Although the PrP-Sc levels were low, the shed placenta may represent a source of infectious prions.
Scrapie is a transmissible spongiform encephalopathy or prion disease, occurring in sheep and goats. First described 300 years ago, scrapie is the prototype prion disorder and the well characterized scrapie phenotypes provided important clues to the origin of kuru and bovine spongiform encephalopathy when they were discovered. Much of the early seminal research on scrapie was based on experimental transmission to goats. Because scrapie in goats is rarely reported in the United States, experimental transmission studies will be useful in pathogenesis, transmission and diagnostic studies. However, the potential for transmission from experimentally infected sheep or goats by the placental route is not well understood. In this study, we examined the placentas from naturally infected sheep and goats for PrP-Sc, the disease-associated isoform of the prion protein. The placentas from naturally infected goats showed PrP-Sc accumulation patterns similar to those observed in naturally infected sheep. However, placentas from naturally infected goats contained only scant amounts of PrP-Sc detectable by immunohistochemistry, enzyme linked immunosorbent assay or western blot analysis. The relative paucity of PrP-Sc in the placentas of goats may represent a source of infectious prions in the areas used for parturition, although the relative risk to copastured animals remains to be determined.