Best I can say about BSE (and related diseases - scrapie, CJD etc) is that it appears to be caused by 'prions'. Prions are types of proteins that have the habit of generating more of their kind when placed in a conducive environment - to that extent they are a lot like viruses. Because, however, they contain no genetic material - neither DNA nor RNA (as viruses do) - it is difficult to classify them as infectious agents. Proteins, in any case, seem to do their job primarily through their shape - the way the amino acid chains are folded up - and it seems that prions merely happen to be proteins whose shape catalyses nearby amino acids to take on the same shape. This, as you can imagine, will trigger off a chain reaction of sorts within an amino acid rich area, thereby starving other cells/functions of the amino acids they require for their functioning. In time, the prions take over the area concerned. As we have seen - brains appear to be particularly vulnerable to these processes - hence the 'mad cow' aspect of the disease.
Since prions aren't viruses or bacteria, killing them, or 'sterilising' food material that contains them, is virtually impossible (I don't think any methods so far have eliminated prions whilst retaining the food - since the sibstances are virtually identical) - hence the danger of eating any prion-infected material.
This is an 'educated' collation on my part, having read a number of articles in the UK concerning the disease. Hope it helps.
On-topic - regarding confusion between human and computer viruses, you might wish to read Neal Stephenson's Snow Crash in which a type of computer virus affects humans. The whole Tower of Babel premise is suitably far-fetched, but the novel is great fun anyway (until the rather OTT ending).
cheer
the sunshine warrior
