If I am not mistaken I heard Turkies are common hosts for Histomoniasis a type of protazoa. For this reason it is not recommended that turkies be house with chickens as chickens may infect turkies, while it is not as deadly to chickens it effets turkies more severely causing mortality.
That being said, I don't know exactly how common it is- most people I know let their turkies and chickens free range together.
Prevention and Treatment:
Because healthy chickens often carry infected cecal worms, any contact between chickens and turkeys should be avoided. Grouse and quail also may carry the infection to turkey yards. Because H gallinarum ova can survive in soil for many months or years, turkeys should not be put on ground contaminated by chickens. Once established in a flock, infection spreads rapidly without the use of a carrier.
(NOT TO SCARE YOU!!! but good info to know and be aware of)