Thanks for the Mad Cow disease president Reagan and daddy Bush

<snip>The US scrapie eradication program was dismantled in 1983 deregulation under Reagan so only lamb and mother, female line within flock were slaughtered, source flock ignored, causing disease incidence to soar and become established and widespread across 39 states according to Hadlow, JAVMA 196 1676 1990. It is hard to know what is going on with US scrapie incidence today due to lack of meaningful reporting standards. There is less of problem in goats though cross-species lateral transmission in mixed flocks seems an unavoidable inference (with relevence to CWD?).

Given the US rendering situation and problems with goats, but prior to developments with BSE in the UK and Stetsonville, the question came up in 1979, could scrapie pass to cows (bovine scrapie) and what is the extent of this disease in the US?

Cattle were successfully inoculated in 1979 in a Mission, Texas APHIS facility both from scrapie passaged in a Suffolk ewe from a pool of 4 scrapie sheep and separately from a passage of goat to goat (co-pastured with same sheep, caprine scrapie). WW Clark et al. Am J Vet Res 56#5 606 1995.

The good news in the Cutlip et al. 1997 paper reviewed here, the cow-to-cow second passage study, is that while the pooled US forms of scrapie considered do indeed induce a transmissible prion disease passagable with consistent symptoms and incubation times in cattle, that disease is clearly not the UK strain of bovine TSE even at second passage when sheep prion protein is long gone. Not particularly spongiform, so technically a TE or BE rather than TSE or BSE. The pathological documentation for this in the paper is excellent.

The bad news is that:

(1) US scrapie easily crosses the species barrier to cattle (and goats). Some other unstudied US strain of scrapie could cause the BSE strain of bovine TSE. The results here clearly disfavor the idea that UK BSE came from sheep, but do not disprove it. The origin of UK BSE remains unknown (as does the much older origin of scrapie). Neither cattle nor sheep prion genotypes nor strain types were determined here.

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