I don't know that much about rabbits but I remember my grandma telling me that you should never eat rabbits unless it is a month with an "R" in it because all the other months the rabbits have worms. What kind of worms, I have no earthly idea. If you notice the months without "R"s are the hot months which would be the months more likely to have flies of any kind. Maybe I am just rambling about some old folks rumor or maybe not, again I have no clue about rabbits but hope it helped or started the ball rolling in the right direction. Good Luck and so sorry your bunny has a worm.
Edited to say:
And now I feel stupid because you were not asking about a rabbit in your thread so maybe I should not post until I am fully awake. Can chickens get worms? Yes definitely!! Can they get the same worms as rabbits? Not a clue. Sorry. I suppose its not entirely impossible though.