Note the paper is about Alzheimer's.

Pisa et al. report [1]:
- 15 AD patients all with fungus in the brain detected;
- 10 controls, none with fungus detected.

They go on to write:

"Proceeding on the assumption that fungi are the aetiological agent of AD, all of the symptoms observed in AD patients can be readily explained. For example, the slow progression of the disease fits well with the chronic nature of fungal infections if they remain untreated. ... Disseminated fungal infections can induce cytokine production ..., which can take place years before the onset of cognitive decline as observed in AD. Thus, this disseminated infection may slowly spread to the CNS and synaptic dysfunction and neuronal loss takes place only when the fungal burden in some areas of the CNS is high. ... The diversity of fungal species that can affect the CNS, as well as the combinations of these species, may account for the observed differences in the evolution and severity of clinical symptoms found in AD patients."

I think this will prove to be relevant to PD too.

Reference:

[1] "Different Brain Regions are Infected with Fungi in Alzheimer’s Disease
Diana Pisa, Ruth Alonso, Alberto Rábano, Izaskun Rodal & Luis Carrasco
Scientific Reports 5, Article number: 15015 (2015)
http://www.nature.com/articles/srep15015

John