Risk assessment

Sheep BSE

In vitro evaluation of the risks posed by serial passage of BSE in sheep

2010: 1 year / Grant: 50 000 euros

Project: BSE has been shown experimentallyto infectsheep. The fact that BSE infected sheep have never been reported to occur in the field, even although sheep were exposed to BSE contaminated feed, could be used to argue that BSE may have adapted on serial passage in sheep and could have evolved a new molecular signature, similar to that of scrapie. The aim of the project was to investigate this potential in vivo scenario using serial PMCA to mimic BSE replication (and perhaps evolution) in different sheep genotypes.

Main results and related published data: BSE seeds could be amplified by PMCA using ovine brain substrates (step 1). Products obtained in step 1 were then used to seed PMCA reaction using ovine brain substrates to model adaptation in sheep (step 2). Amplification products from step 2 exhibited BSE-like molecular features after 1 round of PMCA, but after 8 rounds, a BSE-like or a scrapie-like molecular signature was found depending on the genotype of the sheep, suggesting (genotype-dependent) molecular evolution. Step 2 BSE-like products (round 1 and round 8) could be amplified in PMCA reactions using human PrP substrates, whereas the scrapie-like seeds failed to amplify in human PrP substrates. Extrapolation of these results strongly suggested that BSE can evolve in sheep and come to resemble scrapie at the molecular level, but when this happens the ready ability of BSE to cross the species barrier and transmit to humans is lost.

Genotype-dependent molecular evolution of sheep bovine spongiform encephalopathy (BSE) prions in vitro affects theirzoonotic potential. Krejciova Z, Barria MA, Jones M, Ironside JW, Jeffrey M, González L, Head MW. J Biol Chem. 2014 Sep 19;289(38):26075-88. doi: 10.1074/jbc.M114.582965. Epub 2014 Aug 6.