We only have two chicken left out of ten - the other 8 have died from Mareks disease and the other two are also sick and will probably die shortly. Once our chicken coop is cleared of all the sick chickens can we put a new flock in that same coop? Will a new flock be at risk of Mareks disease from the dirt or the old chicken feces? Is there a way to clean the coop before we add new chickens? Thank you very much.