A German scientist named Braak has published a very interesting series of papers over the last five years or so that may have a bacterial involvement.

One of PD's key features is the Lewy body - sort of a cyst in a neuron. Like it was walling something off. They show up in the part of the brain callen the substantia nigra and are always found there in dead Parkies. If no Lewy bodies are found then you didn't have PD and if found then you did.

What Braak has found is that the LBs actually show up in other areas of the nervous system first and then show up in additional areas in a predictable pattern every time. These areas fall along a route that begins in the nose and another route that begins in the stomach wall. Then they show uo in certain predictable areas one by one following along paths formed by the nervous system. The two paths finally converge after several years at the substantia nigra and you have PD.

Something finds a way through the defences of the brain's olfactory bulb in our nose and also the protections of the stomach wall, then creeps up the vagus nerve and along the olfactory nerves, bypassing the BBB entirely!

We typically lose our sense of smell early on. We know that h pylori is the only thing that can live in the stomach. And that it produces a nasty toxin. We know that at least one virus (polio) starts in the stomach, moves along nerve fibers, and makes similar cyst-like bodies. We know that inflammation makes both the BBB and the lining of the GI system "leaky". We know that bacteria (like h pylori) can cause such inflammation. We also know that sometimes a virus can take advantage of a bacterial infection to slip into the nervous system.

It is not hard to draw the outlines of a situation where something is inhaled and sticks to the mucal membranes of the nose and then through through nasal drip makes its way into the stomach. Over time the nervous system in both areas are penetrated and something goes creeping along the nerves toward the brain.

It could be a virus like polio. It could be a toxin like that found in house dust and made by h pylori. It could an environmental contaminant like the ultra-tiny particles of diesal exhaust. It could be any one or a combination of these or something else altogether.