Chicken diseases are real.I don’t have any real concerns. This is our first time raising chickens and I want to make sure they’re good. They look and act like regular chickens but what do I know. . They free range for several hours a day and there was a suggestion on another thread that wild bird carry different things that can affect a back yard flock.
Wild birds do carry "stuff" but it is my opinion that you are more likely to unknowingly bring home a diseased bird if you don't learn about biosecurity and practice it.
Know that people sell sick birds all day every day.
Be careful who you buy future birds from.
An ounce of prevention...you know the saying.

http://extension.uga.edu/publicatio...&title=Biosecurity Basics for Poultry Growers