We lost our first flock to Mareks. While our ladies are all vaccinated now, it is no guarantee that it won't strike again. We allowed the coop to be empty for about 6 months. During that time we completely cleaned and sanitized the coop with a commercial sanitizer. We also sprayed the ground around the coop as a safety measure. After the 6 month period we allowed chickens back in and haven't lost a bird since. If you like I can get the name of the commercial sanitizer we used. It is well thought of and used in commercial egg farms.