In answer to a recent query, the article about prion-diseases bewing
caused by a Spiroplasma bacterium was written by Frank O. Bastian and was
published in the ASM News, vol 59 #5 in 1993. Apparently, these bacteria
are very small, passing thru pores of 50 nm (?), are neurotropic and very
fastidious in their nutrition, and proteins extracted from them form
fibrils similar to scrapie-associated fibrils characteristic of many prion
disease processes. According to Bastian, as I understand it, antibodies
formed in scrapie-infected animals reacts to these bacteria.