Birmingham, United Kingdom - A provocative new theory about the origin of the "mad cow" and its counterpart human stirred debate at the annual International Congress of biochemistry and molecular biology yesterday. Stanley Prusiner of the University of California, San Francisco (UCSF), suggested that abnormal prion proteins thought to cause bovine spongiform encephalopathy (BSE), as the disease is formally known, can coexist in sheep and prions involved in scrapie, a disease that does not appear to infect humans. If correct, this would mean that the proteins are still hiding sheep.
Since BSE erupted in cattle in the United Kingdom in the mid-1980s, scientists have wondered where the disease came. The studies on the origins of BSE - a fatal disease marked in the early stages of loss of balance - gained urgency with the emergence in 1996 to man the new disease variant Creutzfeldt-Jakob disease BSE-like (vCJD ). Linked to the consumption of beef contaminated with BSE, vCJD has so far killed several dozen people in the UK, France and Ireland. With the extent of the vCJD threat to public health still unclear, scientists have been busy studying the relationship between prion strains blamed for neurodegenerative diseases, including the alleged connection between BSE and scrapie .
Scientists generally assume that BSE arose in cattle whose diet was enriched with a high protein supplement: sheep parts, unfortunately infected with scrapie. While diseases have similar symptoms, BSE prions do not trigger scrapie and vice versa. The main theory is that a technique for rendering the heat mutton pieces which became mandatory in the 1970s somehow modified prions enough to allow them to jump the species barrier and cause BSE and scrapie . (The BSE prions and vCJD prions appear to be identical.)
Challenging this scenario UCSF neurologist Michael Scott and Prusiner, who won a Nobel Prize for the theory that prions cause disease. They think that sheep can be infected by both BSE and scrapie prions, but only because the latter disease in sheep. The rendering process heat, they suggest, may actually destroy or inactivate scrapie prions, opening the way for BSE prions scarcer but more robust to infect cattle. The idea is that scrapie prion could somehow interfere with the infectivity of BSE prions. "It is a kind of selection mechanism. You wipe the scrapie prion labile "by rendering the heat, says Prusiner." Scrapie Prion can even protect human [from BSE]. "
The duo admits they have little evidence to support their proposal but they point to studies in their laboratory mice, which have been modified to be sensitive to both the prion infection of BSE and scrapie. the different strains infected by different brain areas. in . Furthermore, mice infected with scrapie have grown faster disease extrapolating from these results, says Prusiner, "there seems to be a different tank [prion] strains in sheep ': a single action fast that causes scrapie and another slower that causes BSE / vCJD. Because the strain of scrapie spreads faster, Prusiner said, it would greatly outnumber BSE / vCJD strain in infected sheep .
experts contacted by Science NOW are skeptical. Prion expert Moira Bruce of the Institute for Neuropathogenesis unit in Edinburgh for Animal Health said that sheep experimentally infected with BSE become ill almost as soon as the sheep naturally infected with scrapie. "There is no direct evidence that BSE in sheep was" the beginning of the BSE epidemic, she said, even if such a scenario "can not be excluded." And even if 'prion BSE is present in sheep, Prusiner said that there is no reason to avoid eating lamb chops. "in some 25 years of intense study, no one has found signs of transmission [from sheep to humans], "he said.
with reporting by Michael Balter.
0 Komentar