[USCC] composting carcasses in windrows

[wiebebh@mts.net]

As Helane Shields points out:

- research indicates that composting temperatures do not deactivate prions and also that in the 
soils used in once in soil (although 
- Iowa State "Due to many unknown factors regarding the biodegradability of the prions that 
cause bovine spongiform encephalopathy (commonly called BSE or "mad cow" disease), composting 
should NOT be used for disposal of cattle suspected to have BSE."
-  and that in the soils used by  Dr. Joel Pedersen,et al, Wisconsin State,  prions can survive 
for years in soils, and soil can increase the infectivity by a factor of 680.

However, the temperature is not the only potential degradation/deactivation process for prions 
during composting.  They are organic molecules subject to decomposition and this process needs 
careful study before disregarding composting solely based on temperature.  The work of Pedersen 
is important but since soils are highly variable and extremely complex his results apply to the 
soils he used (one should never group all soils and assume they will all react the same way).  
The article you refer to (PLoS Pathogens, July 2007, Johnson et al.) of which Pedersen is a co-
author  indicates that prions bound to montmorillonite increase oral infectivity by a factor 
680.  Montmorillonite is not soil it is a pure clay mineral with a very high charge and a large 
specific surface area and is found in some soils.  Montmorillonite is known to protect soil 
organic matter from degradation by soil microorganisms.  In the same article they report using 
3 different actual soils and found that 2 out of 3 increased infectivity, the third was 
equivalent to unbound prions.  More recently, "Joel Pedersen, Fabio Russo of the University of 
Naples and Christopher J. Johnson of UW-Madison, ... and co-authors  Chad J. Johnson of the UW-
Madison School of Veterinary Medicine, and Judd Aiken and Debbie McKenzie of the University of 
Alberta .. have found that a common soil mineral, an oxidized from of manganese known as 
birnessite, can penetrate the prion's armor and degrade the protein. The new finding, ... was 
reported ...in the Journal of General Virology (Jan. 2, 2009).  

That being said compost is not soil and compost itself is highly variable depending on 
feedstocks.  Therefore we need work looking specifically at prions and SRM/carcasses during the 
composting process.  One researcher working on this is Dr. Xiying Hao at the Lethbridge 
Research Station of Agriculture and AgriFood Canada ( haoxy at agr.gc.ca ).  I am sure if anyone 
is interested they could contact Xiying directly and she would be happy to discuss this in more 
detail.

Brian Wiebe
Winnipeg, MB