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Re: Contaminated bone meal

Square Foot Gardening List - http://www.flinet.com/~gallus/sqft.html

<< It seems to me that if prions can be killed, they must perforce be alive.
 However, if it's true that they cannot reproduce (first time I've heard that
 part), certainly they are operating under a different understanding of the
 word "alive" than you and I are.
  >>

     I should have been more specific and clearer in what I was saying (as 
usual :).
     The prions in transmissable prion diseases (and there are more than just 
BSE) do not have DNA or RNA so are not technically "living." They *cannot* 
reproduce themselves, but *can* cause existing normal proteins to change 
their shape and become destructive in the same way as the disease causing 
prions. 
     Basically, the prion protein (PrP) is on nerve cell membranes in most 
mammals. What BSE and other TSEs can do is change the spape (although not the 
sequence of amino acids) of the PrP into PrPsc and, I believe, PrPc. A change 
in shape from helix to a mainly pleated sheet turns PrP into the destructive 
PrPsc. This is *not* reproduction....and definitely operating under a 
different understanding of "alive" than you and I or even viruses. 
     The don't reproduce and they don't replicate (you may want to confirm 
this for yourself for future use). But they can increase their numbers by 
altering normal proteins. The PrPsc proteins cause other PrP molecules to 
change into PrPsc. There is no immune response to the changed protein, and 
PrPsc is resistant to the protease which would ordinarily destroy the 
protien. The altered protein can't be destroyed, and can eventually build up 
large numbers of PrPsc.....which cause the spongiform damage to the brain and 
CNS. However, there is at least some debate in the medical field whether 
there is a certain number of "changed" prions that need to be ingested or 
otherwise introduced to cause significant changes in PrPs and whether there 
is a "safe" amount that can be ingested with no harmful effects. Then there 
is also the theory that PRPscs entering through a cut or any break in the 
skin is a significantly more effective means of transmission. Regardless, it 
stands to reason that one ingested BSE prion would take longer to produce 
changes in other PrPs......and much longer than if hundreds or thousands or 
millions were ingested.

     They are quite difficult to destroy.....killed is not the right word 
(you're absolutely right :). 
 
     "BSE and scrapie prions are resistant to destruction. Macerated bovine 
brain with the BSE agent and rodent brain infected with the scrapie agent 
were autoclaved at 134oC (Marsh, 1991) to 138oC (Brown, et. al., 1990) for 60 
minutes without complete inactivation. Homogenates of BSE bovine brain 
exposed for two hours to solutions of sodium hypochlorite (16,000 ppm of 
available chlorine) produced no detectable survival of infectivity; exposure 
for two hours to the sodium dichloroisocyanurate solution (16,000 ppm of 
available chlorine) did not completely deactivate infectiveness (Taylor, et 
al, 1994).  Homogenates of BSE-infected bovine brain and rodent brain 
infected with scrapie-agent and exposed to 2M sodium hydroxide for two hours 
did not inactivate the prion agents. High-infectivity hamster-adapted scrapie 
is extremely resistant to heat, chemicals, and processing (Brown, et. al., 
1982). The BSE infective agent is resistant to formalin fixative and 
cremation at 343oC (Marsh, 1991 ) or 360oC (Brown, et. al. , 1990) is 
inadequate to destroy the infectiveness."  

     Sodium Hydroxide is lye, btw. And they can't be destroyed by cremation 
either. Pretty tough buggers, those prions. And, obviously, none of the above 
methods would make infected meat (or milk) suitable for ingestion. I did not, 
however, find any reference to using a combination of heat and 
solvents....although a combination of methods destroying the harmful 
(changed) prions instead of a single one would seem to make a lot more sense. 

<<Thanks, Lisa.  You may be newer to the list than my last set of posts about
BSE (prolly 6-8 months ago).  I'm a writer/editor in the Legislative &
Public Affairs shop at USDA-APHIS.>>

     No, I wasn't around for your last set of posts, unfortunately (but, as 
you work for the USDA, would *love* to ask you some non-gardening questions 
privately). My last microbiology class was more than 6 years ago....and we 
barely touched on prion diseases (and visceral migrans was enough to keep me 
up nights :). And, TSE and BSE information I've come across since has been 
quite contradictory in at least some of the conclusions drawn. 

<<The idea of them pinging around inside brain tissue, making holes, sounds
bizarre.>>

     A paraphrased description from a year old newspaper article on BSE and a 
28 yo man with CJD who believed he was infected by eating the cattle he 
raised (here in Michigan). Whether he was actually infected by eating his 
cattle hasn't been determined. He died within a few months of onset of 
symptoms.

<<It might be useful to find out if the New Guinea women who died of kuru
after consuming the brains of their dead (and spongiform-infected) relatives
got sick after just one of these ritual meals or required many such
exposures to the kuru agent (per Lisa's suggested profile).>>

     It would be hard to determine, since symptoms can take as long as 30 
years to appear (for Kuru) and then the disease progresses rapidly...and 
diagnosis can only be done through examination of the brain and CNS. It might 
be interesting to find the average age of onset of Kuru. But, the cause could 
still be either cumulative ingestion or cumulative changes of PrP to PrPsc or 
another harmful protein shape. Could be both (is probably a combination of 
the two in all TSEs). Couldn't find much on Kuru specifically, and since I 
temporarily took a job in oncology research for a local hospital, I have 
access to all the online medical libraries there and at U of Michigan. 
There's just not too much information on Kuru....not that I could find, 
anyway. Just a few short references in relation to other TSEs.
     I did find (just on the internet) that the UK government has banned 
using bonemeal in commercial farming on fields used by ruminants (because of 
BSE), but not in home gardens. So, the whole thing seems a bit bizarre.
     I do know the issue of BSE, much less all the transmissable prion 
diseases and TSEs, is much too complicated to hash out on a gardening list.
     I'll tell ya, though, I know I'm glad our family is vegan and I've never 
used bonemeal or bloodmeal on anything we grow! :)

Lisa V


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