Human CJD May Be Contagious May 29, 2004 22:00:25 GMT -5
Post by Big Bunny on May 29, 2004 22:00:25 GMT -5
Support for this observation was obtained from an experiment in which scrapie-infected brain material was mixed with soil, placed in a container, and then allowed to "weather" in a semi-interred state for 3 years.9 A small amount of residual infectivity was detected in the contaminated soil, and most of the infectivity remained in the topmost layers of soil, where the tissue had originally been placed--in other words, there had been no significant leaching of infectivity to deeper soil layers.
It is therefore plausible for surface or subsurface disposal of TSE-contaminated tissue or carcasses to result in long-lasting soil infectivity. Uncovered landfills are a favourite feeding site for seagulls, which could disperse the infectivity.10 Other animals might do likewise, and if the landfill site were later used for herbivore grazing, or tilled as arable land, the potential for disease transmission might remain. A further question concerns the risk of contamination of the surrounding water table, or even surface waste-water channels, by effluents and discarded solid waste from treatment plants.
A reasonable conclusion from existing data is that there is a potential for human infection to result from environmental contamination by BSE-infected tissue residues. The potential cannot be quantified because of the huge number of uncertainties and assumptions that attend each stage of the disposal process.
On the positive side, spongiform encephalopathy can be said to be not easily transmissible. Although the level of infectivity to which creatures are exposed is not known, it is probably very low, since sheep that die from scrapie, cattle that die from BSE, and human beings who die from nvCJD represent only a small proportion of their respective
Whatever risk exists is therefore extremely small, but not zero, hence all practical steps that might reduce the risk to the smallest acceptable level must be considered. What is practical and what is acceptable are concepts that will be hammered out on the anvil of politics: scientific input, such as it is, already waits in the forge. A fairly obvious recommendation, based on the science, would be that all
material that is actually or potentially contaminated by BSE, whether whole carcasses, rendered solids, or waste effluents, should be exposed to lye and thoroughly incinerated under strictly inspected conditions. Another is that the residue is buried in landfills to a depth that would
minimise any subsequent animal or human exposure, in areas that would not intersect with any potable water-table source. Certainly, it has been, and will continue to be, necessary in many instances to accept
less than the ideal.
Laboratory of Central Nervous System Studies, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
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