count me as another fan of Molly's herbals.
My flock is in a good sized run, but they tend to stay under the coop and under the pines - and that is where the droppings build up. So, yup, worms. This spring I have grandiose plans of digging out under the coop (its an old construction trailer) and hauling that dirt to the garden and replacing it with garden dirt.
Having the chickens in the run for 8 or 9 years means there is a pretty good build up of cysts. I've had to keep them more confined the last year because a neighbor dog from down the road was picking them off. I doubled the run - its about 1,500 feet , but still, the flock has its favorite places to be.
I could move the coop and run, but I'm happy where it is, and it would be quite the underaking to move the coop, run fence, etc.
I do think health helps a chicken handle the normal worm load, but even a very healthy chicken can get overrun - stress, age, change, etc.
I wonder if there's a way to treat the affected ground to kill off the eggs without harming the chickens/other life? Now THAT would be great! My main run is muddy muck for about half the year. At least twice a year I scrape off the top poo layer to bring it back down to fresh earth and that seems to help. I do the same to the coop floor (it's dirt) but much more frequently.