The first experimental evidence that scrapie, a prion disease mostly affecting sheep, has the potential to infect humans, is presented online this week in Nature Communications. Prion diseases are fatal neurodegenerative disorders that affect a large spectrum of mammalian species.
Prion diseases are caused by infectious, malformed prion proteins that interact with normal prion proteins and cause them to deform and accumulate in the body. The ability of prions to break the transmission barrier between species is determined by compatibility between the prion protein of a given host and the misfolded, infectious prion particle. In humans, the most common form of prion disease is sporadic Creutzfeldt-Jakob disease (sCJD), which is considered to be a spontaneous disorder. Bovine Spongiform Encephalopathy (BSE), a prion disease that occurs in cattle, is the cause of variant Creutzfeldt-Jakob disease (vCJD) in humans. The potential of scrapie prions to infect humans was unknown.
Olivier Andreoletti and colleagues investigate this potential using a mouse model that has been genetically engineered to express the human prion protein. The same model was previously used to confirm the ability of BSE to infect humans during the 1996 outbreak of vCJD in the United Kingdom. The authors show that a panel of sheep scrapie prions transmit to several of these mouse models with efficiency comparable to that of cattle BSE. The transmission of different scrapie prions in these mice also led to the propagation of prions that appear identical to those causing sCJD in humans.
These results suggest that scrapie prions may have the potential to infect humans and raise new questions about the possible link between animal and human prions. However, this study is not conclusive as it does not directly show transmission to humans; therefore, more research will be needed to confirm that there is a link.