Tim Buss (tbuss at fred.fhcrc.org) wrote:
: I was told the infectious material (in brain pastes) isolated from
: cows differs from the original scrapie form. It is more infective and
: more resistant to high temperatures, so does anybody know how many
: different forms are out there? It seems a bit premature to assume humans
: are immune to this disease.
If by "the original scrapie form" you mean the sheep form, Prusiner's theory
about species barriers would explain this. He has used molecular biology
and transgenic animals to show that the longer latency period when infecting
across different species is due the differences in sequences of the prion
protein across different species. It appears that infectious protein
"recruits" the endogenous prion protein in its propagation thru the CNS, and
this takes longer if the sequences of the infectious protein and the endo-
genous protein differ. This also means that infectious material coming from
a sheep with scrapie will be different (in sequence) from that coming from a
cow with BSE. This different sequence may be more or less heat-sensitive,
more or less infectious in humans, etc.
With respect to the latter, some prion isolates SHOULD certainly be infectious
to humans, because the transmissible human spongiform encephalopathy kuru
seems to involve particles derived from the human homolog of the same prion
protein precursor that is involved in scrapie, BSE, Creutzfeld-Jacob,
Steven W. Barger, Ph.D.
Sanders-Brown Center on Agin