Prions not destroyed by incineration?

[Mike Ewall <catalyst@envirolink.org>]

>Also has anyone any data on dioxin emissions from a BSE/cattle incinerator
>anywhere in the world?  As cattle, as a food, are a major source of our
>bodies dioxin contamination, surely these chemicals must be released into
>the environment when cattle, with BSE or not, are disposed of by
>incineration?

I can't speak to the dioxin issues in BSE/cattle incinerators, but I was
just checking out http://mad-cow.org/ (a very comprehensive website on the
topic) and the fact that prions are hard to destroy, even in incinerators
is quite disturbing.  Below are a few of the notable issues that I found
through that website's search engine.

Mike
------

http://cyber-dyne.com/~tom/biol_tse.html#res
Resistance of the agent to destruction

Chemical disinfectants (e.g. domestic bleach), weak acids, DNAase, RNAase,
proteinases (including those found in the animal gut), ultraviolet light,
ionising radiation, heat (cooking tempertures), and chemicals that react
with DNA (psoralins/UV light, hydroxylamine, zinc ions), all have little
effect on the infectivity of the agent. High temperature autoclaving (135
degrees centegrade for 18 minutes) decreases the infectivity dramatically,
as does the use of 1M NaOH, but neither will fully destroy the agent, as it
has been found to remain infective after 360 degrees C for 1 hour or even
after incineration. Internment of infective tissue in the soil for three
years did not destroy the agent. Some phenols and proteases will decrease
the infectivity of the agent but not to an adequate degree to be of value
in disinfection. 

http://cyber-dyne.com/~tom/well_apr14.html
Making the picture even bleaker is the resiliency of prions. They are not
destroyed by the usual means used to kill infectious agents. They are
resistant even to boiling at temperatures as high as 250 degrees Celsius
(well over 400 degrees Fahrenheit).  They are also resistant to ionizing
radiation. 


http://cyber-dyne.com/~tom/current_UK_news.html
Yesterday, the realisation that people who harbour the new variant may be
capable of passing on the infection through operations fuelled calls for
new rules on disposal of surgical instruments , since the prion protein
survives standard sterilising processes. Prof Liam Donaldson, the
Government's Chief Medical Officer, said: "We are looking at the
possibility of disposable instruments but in any field it is the matter of
balancing different sorts of risk.

This raised the prospect of using disposable instruments wherever possible
because "there is no means of sterilising surgical instruments adequately
against prions ".


http://cyber-dyne.com/~tom/May97_news.html
Prions don't need to be soluble to leach into the water table. My point is
again that we simply don't know what the level of risk is.  The phrase used
about nv-CJD is that the most likely hypothesis is "exposure to the BSE
agent". Nobody said by what medium.


http://cyber-dyne.com/~tom/blood_supply.html
Although organ tissue carries the greatest risk, animal studies do suggest
that meat itself can transmit prion-related diseases. However, we cannot
exclude the possibility that milk could also carry disease-inducing prions.

Eating the flesh of other animals (besides cows) or drinking their milk may
not be safe either. These other animals may also be affected with a
prion-related diseases. As we have already mentioned, sheep as well as
goats can become infected with such illnesses. Even if some of these
illnesses do not seem to be easily transmitted to humans (because of what
is often called, "the species barrier"), the possibility exists that
different strains of prions could present more danger.