Two more years have passed.

The aetiology of Parkinson's is still unknown. In a number of posts that I've made in the past, in both this and other threads, I've used epidemiological data to suggest an association between fungal infection and PD.

In this paper [1] Berstad and Berstad present the hypothesis that "a causative agent in [PD] might be either a fungus or bacteria with fungus-like properties".

Reference:

[1] "Parkinson's disease; the hibernating spore hypothesis"
K. Berstad, J Berstad
Medical Hypotheses, July 2017
Parkinson’s disease; the hibernating spore hypothesis - ScienceDirect

John