A few other things to consider:
Are there any local starling roosts?
Do you have any bats in the roof?
See the thread "Histoplasma capsulatum" that shows the epidemiological evidence that suggests a link between this fungus and PD. The faeces of bats and starlings allows the fungus to grow.
http://neurotalk.psychcentral.com/thread170268.html
Is there a history of Lyme Disease in the area?
It may be that the house is not important, but other common ground is, e.g. your parent's house.
John