GerryW, thanks very much for your substantial post. There are a number of things there which I will look into.

One point I would like to make at this stage is that I think your statement "A recent Chinese study confirmed the role of infections in PD" could be a bit misleading. I read this paper recently and I remember that they do not claim to have established causality. All they claim to have established so far is that "infectious burden" (i.e. the number of different infections you've had during your life) is greater in PWPs compared with non-PWPs. I would agree though, that they have certainly established a relationship between infection and PD.

Perhaps I'm splitting hairs once again!