Viral infection may be a factor in accelerating neurodegeneration in the mid brain.

[Farooqji]

sciencedirect.com/science/a...

[MarionP]

Something related: some while ago I happened upon a study of an asian-sourced flu virus, I think the same "Spanish" flu that wiped out many people in 1918, that when introduced to mouse brains cut a wide swath, just killed the cells outright, in substanta nigra and several hypothalamic and amygdala or hippocampus, just going from memory here (ironic, that, eh?) regions.