In the process of getting a copy of John's reference, I came across a good source of background information (IMHO):

Avian Flu Diary: Nature Comms: Revisiting The Influenza-Parkinson's Link

... and buried within all that background information is a link to the research paper that was the subject of John's previous post (07-31-2013):

"Highly pathogenic H5N1 influenza virus can enter the central nervous system and induce neuroinflammation and neurodegeneration", Jang H, Boltz D, Sturm-Ramirez K, Shepherd KR, Jiao Y, Webster R, Smeyne RJ. PNAS August 18, 2009 vol 106 no. 33, doi: 10.1073/pnas.0900096106.

Highly pathogenic H5N1 influenza virus can enter the central nervous system and induce neuroinflammation and neurodegeneration

(this is an open-access document)