Well,
Farm Boy logic tells me that if redworms/earthworms are feeding on chicken poo their is a slight chance of parasites such as round worm and gape worm. HOWEVER, I feel if the redworms/earthworms have not been associated or feeding on the droppings of chickens. The chance is very very slim.
SO, I raise worms and feed worms to my chickens on occasion, I do feed chicken poo to my worms. My birds free range, if they find a worm in the woods I do not worry about it.
I personally question the few studies out there. Most of these studies are done in massive factory farm type settings with huge flocks and all...
Just my opinion...
ON