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The brain eaters:

A medical detective story behind our understanding of Mad Cow

Part 3: The prion connection: not a virus after all?

Some uncertainty still remains about the causes of spongiform encephalopathies. Most scientists now agree that they aren't caused by viruses. As described in our virtual textbook pages on Mad Cow the strongest hypothesis to explain SE's was proposed by researcher Stanley Prusiner. Back in the early 70πs, Prusiner became interested in scrapie, a kind of SE found in sheep. (It was called "scrapie" because affected sheep repeatedly scrape their bodies against the walls of their pens.) After many experiments, Prusiner proposed that scrapie was caused by an entirely new kind of infectious agent, a kind of protein that Prusiner called prions.

Stanley Prusiner

Prions are so radically different from any known form of life that they are still controversial among biologists, even though Prusinerπs work earned him a Nobel Prize in 1997. Prions contain neither DNA nor RNA. This helps explain some of their more frightening abilities. They are not affected by sterilization techniques that kill all known disease-causing organisms and most viruses. Superheated steam in autoclaves doesnπt touch them. Intense bombardment with radiation and soaking in formaldehyde does nothing either. Whatπs more, prions can cause disease after being buried for years or being frozen for decades. (So forget about just cooking your meat a little longer!)

It is now generally accepted that prions cause several forms of SE's in livestock, including Scrapie in sheep and Mad Cow -- officially called Bovine Spongiform Encephalopathy (BSE). Evidence was mounting that prions are also responsible for vC-JD. But how could those prions have spread so rapidly through cows? How did they jump to humans? And why did all this happen when it did?

For more information:

Kuru: The Dynamics of a Prion Disease

http://www.as.ua.edu/ant/bindon/ant570/Papers/McGrath/McGrath.htm

National Institute of Neurological Disorders and Stroke Kuru Information Page

http://www.ninds.nih.gov/health_and_medical/disorders/kuru.htm

	Why has the prion hypothesis been so controversial among biologists? Can you think of another situation during the last 30 years in which the cause of a new disease was difficult to identify — and then controversial for some time?
Continue the Story Part 4: Where's the beef? Part 5: What we know now — and what don't we know
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