from food:

www.ncbi.nlm.nih.gov/pmc/articles/PMC5701169/

• so human source probably also possible
• leaky gut probably a factor

According to research from John Hopkins, Duke University, and Utah State University, caregivers of someone with neurodegenerative disease are six times more likely to develop the condition themselves. Neurodegenerative disease is a spectrum disease.

Resection of the vagus nerve before rotenone treatment stopped the spread of PD-like pathology.¹³ Taken together, these data support the intriguing Braak and prion hypotheses of PD development.