When sprayed into the air, prions that cause mad cow and other neurodegenerative diseases may be in one of their most lethal forms.
A new study has revealed one short exposure to sprayed prions can be 100 percent lethal in mice. While the discovery doesn’t present any foreseeable public health threat, it comes as a surprise to scientists who study prion-based diseases and calls existing safety rules for laboratories and slaughterhouses into question.
“Common knowledge is that prions aren’t airborne, and can’t cause infection that way,” said neuropathologist Adriano Aguzzi of University Hospital Zurich, co-author of a study appearing today in PLoS Pathogens. “We were totally surprised and also a bit frightened at how efficient [airborne infections] were.”
Most infectious diseases are spread by bacteria or viruses, which use genes to copy themselves. But prions are a third form of disease discovered in 1982, and they’re made only of misfolded proteins. The molecules resemble regular proteins found in the brain cells and other nervous tissues, but their abnormal shape converts healthy proteins into long fibrils that ultimately kill cells.
Like a chain reaction, fibrils create more prions until the host dies from destroyed brain and nervous tissue. All prion infections are 100 percent fatal, and symptoms appear suddenly months or years after infection.
“Prions are like an enemy within, the alien in some B-movie that transforms people to an evil version,” said prion biologist Edward Hoover of Colorado State University, who was not involved in the study. “The immune system doesn’t see them coming.”
Five known human prion diseases exist, including Creutzfeldt-Jakob disease, as well as six non-human diseases, including scrapie, chronic wasting disease and mad cow disease (which sometimes jumps to humans through contaminated meat)....
“My real hope in studying prions is apply what I learn to much more common but similar diseases, such as Alzheimer’s,” Aguzzi said. “Knowing why aggregated proteins damage neurons will allow us to understand how they affect brain function.”
via Airborne Prions Make for 100 Percent Lethal Whiff | Wired Science | Wired.com.
Friday, January 14, 2011
Airborne Prions Make for 100 Percent Lethal Whiff
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4 comments:
It's important to note the distinction in this case between "aerosolized" and "airborne" - mice in the study were exposed to high concentrations of infected tissue via aerosol, not simply infectious particles that traveled through the air.
Infected mice housed with uninfected mice did not transmit the infection, and the author admits the concentrations used were unrealistic - it's more important for proof of concept. There is no evidence that prion diseases can be transmitted through the air naturally.
But, still is "aerosolized" as in being "sprayed into the air" really that far removed from prions, which are nothing but proteins, being "airborne"?
How much would it take for a protein to go from aerosolized to airborne?
How large are dust particles and chemicals that travel the air currents? We know that pollen, viruses and bacteria that travel the air currents are all larger than proteins.
And, Adriano Aguzzi did say, he was "a bit frightened at how efficient [airborne infections] were."
Although the article did say that "all mice except one group, which was exposed to a very light concentration of prions, got infected and died about 150 to 200 days after exposure."
It added ...
"When it came to a lethal dose, the researchers also found that prion concentration didn’t matter as much as exposure time. A group of four mice exposed for one minute to a light dose of prion-infected fluid, for example, died from scrapie in about 200 days."
Yes, there is no proof that prions can be distributed via air currents in the natural environment, but the concern is about the unnatural environments such as that of the slaughterhouse.
Ann,
I am not contesting the fact that prion-sized proteins can travel in respiratory droplets, etc. like viruses - obviously something small enough to be a constituent of a virus has the potential to do so as well.
I'm contesting the conclusion that some have drawn from the results of the article, which is: since aerosolized brain tissue containing prions can infect mice, prions must therefore be transmissible by sharing air with an infected individual.
For a disease to be considered "airborne" it must be "shed" in some manner - e.g. in respiratory droplets, urine, etc. However, this is not enough - it also must be shed in infectious amounts (i.e. enough must be passed from one individual to another to sufficiently inoculate the uninfected individual).
If this were the case, family members of those with sporadic cases of CJD and people who've provided care for or studied individuals with some type of TSE would have also contracted the disease at the height of its infectivity, through close contact. There is no evidence that this is the case.
The researchers essentially mashed up infected tissue and sprayed it at the mice, in high concentrations - this doesn't happen outside of the laboratory setting. Also, I'll repeat that uninfected mice did not contract the disease from infected mice.
They discovered another route by which you can infect something/someone with prions, not another route by which prions infect people - big difference!
Sorry, I didn't see where people thought, after reading the study, "prions must therefore be transmissible by sharing air with an infected individual."
I was merely commenting on the article, which said as I wrote, which agrees with what you had originally said: "aerosolized" or "airborne" transmission enough to cause prion illness does not occur in the natural environment.
But, that doesn't mean such transmissions can't occur in the unnatural environment of a slaughterhouse. Or, for that matter, in the unnatural environment of a biological war, given improved dispersal techniques. (Nothing like giving contrail/chemtrail theorists something else to worry about, though.)
By the way, please be careful to whom you point your "yous": "They discovered another route by which you can infect something/someone with prions ... ." I've never worn and never plan to ever wear a military uniform, thank you God!
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