In multiple system atrophy (MSA), progressive neurodegeneration results from the protein α-synuclein misfolding into a self-templating prion conformation that spreads throughout the brain. MSA prions are transmissible to transgenic (Tg) mice expressing mutated human α-synuclein (TgM83(+/-)), inducing neurological disease following intracranial inoculation with brain homogenate from deceased patient samples. Noting the similarities between α-synuclein prions and PrP scrapie (PrP(Sc)) prions responsible for Creutzfeldt-Jakob disease (CJD), we investigated MSA transmission under conditions known to result in PrP(Sc) transmission. When peripherally exposed to MSA via the peritoneal cavity, hind leg muscle, and tongue, TgM83(+/-) mice developed neurological signs accompanied by α-synuclein prions in the brain. Iatrogenic CJD, resulting from PrP(Sc) prion adherence to surgical steel instruments, has been investigated by incubating steel sutures in contaminated brain homogenate before implantation into mouse brain. Mice studied using this model for MSA developed disease, whereas wire incubated in control homogenate had no effect on the animals. Notably, formalin fixation did not inactivate α-synuclein prions. Formalin-fixed MSA patient samples also transmitted disease to TgM83(+/-) mice, even after incubating in fixative for 244 months. Finally, at least 10% sarkosyl was found to be the concentration necessary to partially inactivate MSA prions. These results demonstrate the robustness of α-synuclein prions to denaturation. Moreover, they establish the parallel characteristics between PrP(Sc) and α-synuclein prions, arguing that clinicians should exercise caution when working with materials that might contain α-synuclein prions to prevent disease.