The Naked Scientists

The Naked Scientists Forum

Author Topic: How are infectious prion diseases, like BSE, transmitted?  (Read 35673 times)

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 1144
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #25 on: 23/10/2003 05:17:31 »
I read the article, but it really only applies to highly processed foods that can't really be hurt by drastic pressure and heat.  I don't think a steak would survive in recognizable form.  Maybe the process could be adapted though.

Personally, I think brains are very good when they are cooked right. I've never been much on the other end of the animal. [:p]

------------------------
No words of wisdom here.
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #26 on: 23/10/2003 10:34:05 »
Prion is a termed coined by nobel prize winner Stanley Prusiner and stands for "proteinaceous infective particle" (they switched a couple of lettes around to make it sound better !)

Like enzymes, prions are proteins; they are not alive and cannot be 'killed'. But they can be 'denatured' which means affecting the function of the protein by altering its structure. So when a steak goes in the pan it changes colour, consistency and taste because the proteins it contains permanently change their shape (conformation) in response to the heat of the cooking process.

In the brain the normal prion protein - PrPc - is a globular shape. We don't yet know what it does. But the prion protein can also exist in the form of a flattened fibrous sheet. This is the pathological prion found in scrapie, CJD and BSE. It's referred to as PrPsc and it is very stable and  heavily resistant to breakdown enzymically, chemically or with heat and other denaturing agents. It is a problem because this abnormally shaped PrPsc prion protein can, rather like a religious fanatic, go around inflicting itself on normal prions and forcing them to change to the abnormal form too. So in this way, the conversion of the brain's healthy Prpc to PrPsc follows a positive feedback loop because you make more abnormal prions that can then co off an convert more normal prions to the abnormal form. The proces therefore accelerates exponentially. The accumulation of the fibrous prion proteins in the brain produces pathological effects including neuronal cell death and the ensuing dementia.

The evidence for this mechanism is that high levels of the abnormally folded prion protein are found in the brain at death. Mice that have been genetically engineered to lack the normal prion protein can't get the disease. And people who have had brain surgery and been operated on using the same instruments (autoclaved) as someone who has subsequently developed CJD, themselves have gone on to develop CJD.

An interesting, though rare, disease. Your chance of getting it is less than being hit by lightning. The sporadic disease (CJD) crops up with a frequency of about 1 person in a million per year. Hence there are about 60 cases a year in the UK. BSE is much more difficult to predict because all of the victims so far have all shared a gene in common, suggesting that there might be an inherited susceptibility to the disease. Since that gene type is carried by about 20% of the population the future is difficult to predict, although the anticipated number of human cases of BSE has now been hugely down-graded from the terrifying suggestion of "millions" a few years ago to "hundreds" now.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 1144
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #27 on: 23/10/2003 19:26:02 »
Thanks Chris - That is the best description of prions and the various diseases they cause I've yet to hear.

John
 

Offline bezoar

  • Hero Member
  • *****
  • Posts: 950
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #28 on: 23/10/2003 21:30:45 »
It would seem that if the abnormal prions can go about coercing the normal ones to go abnormal, then there should be a way to reverse the process, with the normal ones coercing the abnormal ones to go normal.  Theoretically, there should be a cure, and maybe it should focus on the resistance and reactivity of the normal prions.

And Chris, do you eat beef?
« Last Edit: 23/10/2003 21:31:35 by bezoar »
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #29 on: 23/10/2003 22:04:45 »
Bezoar - I did reply to your beef enquiry - see above ! Maybe you've got BSE and forgot ;)

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline genegenie

  • Full Member
  • ***
  • Posts: 85
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #30 on: 23/10/2003 22:42:43 »
Great idea bezoar! Perhaps when they figure out how the variant protein alters the normal protein, that could be possible. I suppose I just don't like the idea of inactivation by denaturation, because I think about how easily renaturation occurs in heat denatured DNA. But of course, I'm speaking out of total ignorance [8D]....just my thoughts.[?]
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #31 on: 23/10/2003 23:20:49 »
There is a trial on-going with an agent derived from beech chippings called pentosan polysulphate which is administered intraparenchymally - i.e. directly into the brain. In the one case for which there is robust evidence at the moment it seems to have halted the progression of the disease, and produced some modest functional improvements. The agent is believed to hinder the interaction between the abnormal prion and its healthy counterpart.

However it is worth bearing in mind that most of the symptoms of the condition are due to neuronal cell death and so treatment isn't merely a case of removing the pathological deposits.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline bezoar

  • Hero Member
  • *****
  • Posts: 950
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #32 on: 24/10/2003 13:08:28 »
But isn't the neuronal cell death triggered by the abnormal prion?
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #33 on: 24/10/2003 14:27:40 »
Yes, that's what we believe. But my point is that the disease only becomes clinically manifest, and robustly diagnosable, once there has been (considerable) neuronal cell death. To reverse the effects of the clinical syndrome you would need to not only prevent the further accumulation of pathological prions, but also replace the lost cells.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 1144
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #34 on: 24/10/2003 21:43:07 »
Is it possible to replace the lost neuronal cells?  If so, how would the new cells be "trained" back into the neural network? I guess what I'm asking is wouldn't the person's memories and skills be lost?

John
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #35 on: 25/10/2003 00:05:22 »
That's essentially what people are trying to achieve with stem cell therapy, and neuronal cell grafts taken from foetal tissue. It has shown some promise in patients with Parkinson's Disease, and a trial is underway on Huntington's too.

The reality is that we have no way of knowing how well the new cells integrate into the existing neural network and we have to go on clinical observations only, which could be confounded by a host of factors.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline bezoar

  • Hero Member
  • *****
  • Posts: 950
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #36 on: 25/10/2003 03:50:51 »
Isn't kuru also a prion disease?
 

Offline Ylide

  • Moderator
  • Hero Member
  • *****
  • Posts: 905
    • View Profile
    • http://clem.mscd.edu/~mogavero
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #37 on: 25/10/2003 06:56:36 »
Tweener:

Since prions exist in and infect brain matter, your chances of getting one from a steak are pretty slim, even from an infected cow.  Processed meats are where the danger lies.  And since processed meats can be treated (or will be able to be treated in the near future) I wouldn't worry too much about it.  

In the meantime, if you're really worried about it, avoid processed meats, ground beef (unless you pick out the cut of meat and have them grind it right in front of you), and all types of sausages.

This message brought to you by The Council of People Who Are Sick of Seeing More People
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #38 on: 25/10/2003 12:18:29 »
quote:
Originally posted by bezoar

Isn't kuru also a prion disease?



Yes, it was prevalent among the Fore people of New Guinea who practised ritualistic cannibalism which involved eating the brains of dead relatives. Since it was mainly the women that carried out the ritual, the disease predominated amongst the females of the tribe. It disappeared once the practise ceased, indicating the capacity of infectious prions to be transmitted via the oral route.

Kuru actually means "he who trembles" and is a reference to the symptoms experienced by sufferers as the disease becomes manifest and they develop involuntary movements. In some cases these involuntary movements were sufficient to throw some people into their camp fires, though whether they did this partially voluntarily in an attempt to escape the symptoms tey were experiencing, no one knows.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline Ians Daddy

  • Hero Member
  • *****
  • Posts: 532
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #39 on: 25/10/2003 14:30:48 »
That is an interesting story. You guys never cease to amaze me. That's a good story just in time for Halloween.
 

Offline bezoar

  • Hero Member
  • *****
  • Posts: 950
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #40 on: 28/10/2003 03:58:17 »
Oh, I thought you meant the rest of the tribe threw them into the fire.  Thought they were just preparing the next meal.  I didn't think the symptoms were painful at all.  My impression was that it was just a gradual neuro degeneration.
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #41 on: 28/10/2003 11:33:22 »
It causes mental anguish owing to the psychiatric changes experienced by some - uncertainty and stress caused by the symptoms. BSE sufferers frequently do complain of pain because the normal systems that relay pain stimuli to the brain and control our perception and conscious experience of pain are disturbed by the disease process.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline puddintame

  • First timers
  • *
  • Posts: 7
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #42 on: 01/12/2003 23:07:27 »
Topic of "Prions" and "BSE" from October, 2003 talking about other types of contamination that perhaps have occurred or are known to have occurred.  My physician had recommended melatonin, but cautioned me to be sure that it was synthetic and not produced from 'cow'.  It proved to be a study in 'who knows'.  In searching it out I found that most folks having this product on their shelves knew very little about it.  Most assured that they stocked nothing but synthetic and this subsequently proved to be true in most cases.  Interesting subject matter in this article.  The pursuit of how prions function is facinating and we are hearing a lot about the scientists' interest in them these days.
 

Offline pixcdust

  • First timers
  • *
  • Posts: 1
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #43 on: 15/01/2004 00:25:15 »
Why doesn't our body break down the BSE? Why are Prions processed by oral ingestion and not destroyed by our enzymes? I need answers, I am a college student and this is for extra credit can someome please help, thanks.
 

Offline Ylide

  • Moderator
  • Hero Member
  • *****
  • Posts: 905
    • View Profile
    • http://clem.mscd.edu/~mogavero
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #44 on: 15/01/2004 08:21:05 »
You can't uncook a steak.  The intermolecular forces that fold proteins together are not quite the same in frequency and structure that bind DNA.  

Do they have any idea at all how prions do what they do?  Is it a genetic change where RNA is creating proteins incorrectly, or do they alter existing proteins?



This message brought to you by The Council of People Who Are Sick of Seeing More People
 

Offline genegenie

  • Full Member
  • ***
  • Posts: 85
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #45 on: 23/01/2004 13:00:39 »
They alter existing proteins apparently. There's an intersting article at http://www.cyber-dyne.com/~tom/prionSP.html which also talks about genetic susceptibility to prion disease. Nasty stuff!!
 

Offline Big_Jules

  • Jr. Member
  • **
  • Posts: 10
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #46 on: 09/04/2004 02:56:02 »
To add another layer to this discussion, there is variation in the sequence of bases in the gene and hence the sequence of amino acids (building blocks) in normal prion protein among any animal species, including us. Such differences also confer a greater disposition to heritable neurodegenerative diseases such as conventional CJD. It appears that certain of these variations make the normal prion protein more or less susceptible to confirmational change induced by the 'rogue' prion protein. Several of these sequences have been identified. Presumably, interaction between key amino acid sequences in the rogue and normal proteins enact the conformational change. As Chris has stated, the beta-sheet conformation appears to be highly resistant to enzymatic digestion, so that enzymatic digestion, specially within neural tissue, is unlikely. With respect to antibodies, one would imagine that the indigenous protein, while changed in shape, would still be recognised as 'self' and not susceptible to immune attack.
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #47 on: 09/04/2004 06:07:20 »
The point is Jules, that since the abnormal form of the prion protein seems to be heavily resistant to digestion with proteases, it is hard to envisage how an antigen presenting cell could chew it up and present it effectively in the first place, in order to initiate an immune response. This may be why there is so little immune response to the accumulating pathological prions.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline Big_Jules

  • Jr. Member
  • **
  • Posts: 10
    • View Profile
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #48 on: 09/04/2004 02:56:02 »
To add another layer to this discussion, there is variation in the sequence of bases in the gene and hence the sequence of amino acids (building blocks) in normal prion protein among any animal species, including us. Such differences also confer a greater disposition to heritable neurodegenerative diseases such as conventional CJD. It appears that certain of these variations make the normal prion protein more or less susceptible to confirmational change induced by the 'rogue' prion protein. Several of these sequences have been identified. Presumably, interaction between key amino acid sequences in the rogue and normal proteins enact the conformational change. As Chris has stated, the beta-sheet conformation appears to be highly resistant to enzymatic digestion, so that enzymatic digestion, specially within neural tissue, is unlikely. With respect to antibodies, one would imagine that the indigenous protein, while changed in shape, would still be recognised as 'self' and not susceptible to immune attack.
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #49 on: 09/04/2004 06:07:20 »
The point is Jules, that since the abnormal form of the prion protein seems to be heavily resistant to digestion with proteases, it is hard to envisage how an antigen presenting cell could chew it up and present it effectively in the first place, in order to initiate an immune response. This may be why there is so little immune response to the accumulating pathological prions.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

The Naked Scientists Forum

Re: How are infectious prion diseases, like BSE, transmitted?
« Reply #49 on: 09/04/2004 06:07:20 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums