After contemplating on the parasite I have, and the complicity of it, I have thought about similar strains that could be really nasty.
Since these things have a certain amount of tolerance in the immune system, they have a certain freedom of movement within the host.
I have also been wondering if I inherited the parasite at birth, which is a possibility with these types.
That calls into question, the history of ancestral stem-lines.

If, for example, the parasite jumps through several generations, and survives [think animals as well] is it not possible to evolve to a point where there could be symbiosis with host cellular functions?
If the parasite could manufacture peptides [which it does] could this not directly effect our behaviour?
Our thoughts, are based on chemicals\molecules acting on cells. In this respect, the parasite could evolve to embed it's own instuctions to act upon these processes.
Could an animal, or human act out, based on impulses received by a parasitic entity? I don't see bacteria or viruses doing this, but certain fungus might.

parasites are designed to survive in a host, while keeping a discreet presents.
The motives of such a relationship, could perceivably allow the host to become more than just a physical host, and also become part of the host personality.
It could explain the motives of many people who act out in weird, ways.

I know there are studies on this, and I never really looked into it. It would be an interesting subject to blog.

http://www.sciencedaily.com/releases/2006/08/060804085444.htm

Shroom