BSE transmission to humans

BSE transmission to humans - Compelling transgenetic...

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Compelling transgenetic evidence for transmission of bovine spongiform encephalopathy prions to humans Michael R. Scott* ²‡ , Robert Will § , James Ironside § , Hoang-Oanh B. Nguyen*, Patrick Tremblay* ² , Stephen J. DeArmond* ²¶ , and Stanley B. Prusiner* ² i *Institute for Neurodegenerative Diseases, Departments of ² Neurology, i Biochemistry and Biophysics, and Pathology, University of California, San Francisco, CA 94143; and § National CJD Surveillance Unit, Western General Hospital, Edinburgh EH4 2XU, United Kingdom Contributed by Stanley B. Prusiner, October 27, 1999 There is growing concern that bovine spongiform encephalopathy (BSE) may have passed from cattle to humans. We report here that transgenic (Tg) mice expressing bovine (Bo) prion protein (PrP) serially propagate BSE prions and that there is no species barrier for transmission from cattle to Tg(BoPrP) mice. These same mice were also highly susceptible to a new variant of Creutzfeldt–Jakob disease (nvCJD) and natural sheep scrapie. The incubation times ( 250 days), neuropathology, and disease-causing PrP isoforms in Tg(BoPrP)Prnp 0/0 mice inoculated with nvCJD and BSE brain ex- tracts were indistinguishable and differed dramatically from those seen in these mice injected with natural scrapie prions. Our find- ings provide the most compelling evidence to date that prions from cattle with BSE have infected humans and caused fatal neurode- generation. T here is growing concern that bovine spongiform encepha- lopathy (BSE) may have passed from cattle to humans, resulting in 50 cases of an atypical, new variant of Creutzfeldt– Jakob disease (nvCJD) in teenagers and young adults (1–4). Epidemiological findings (2, 4), gel electrophoresis of the prion protein (PrP) (5), and transmissions to inbred mice (6, 7) and primates (8) have each raised the possibility of a link between BSE and nvCJD. More than 175,000 cattle, primarily dairy cows, have died of BSE over the past decade (9). How many more cattle were exposed to BSE prions but slaughtered before developing clin- ical signs is uncertain (10). Given the enormity of the affected cattle population in the United Kingdom, a means of assessing risk to the human population is paramount (9), and more sensitive methods for detection of prions are urgently needed (11). The magnitude of the potential risk to the human popu- lation is still speculative, but the death rate from nvCJD per year had remained approximately constant until recently, when a disquietingly high number of deaths from the disease, a total of nine new cases, was reported in the last quarter of 1998 (4). Although it is not yet known whether this trend will continue, the possibility that a large section of the population is at high risk must be seriously entertained. In assessing this potential risk, it is generally assumed that humans would benefit from some degree of protection from exposure to BSE prions because of the ‘‘species barrier.’’ This term refers to the relative lack of susceptibility of one species to prions derived from another species (12). Transgenic mice
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