Mareks is a bit of an unknown. Some sources say it can remain in your environment for as much as seven years after the chickens are gone. So every new chicken should be vaccinated and kept away from any dust or dander, or from the coop of the infected birds until they are 2-3 weeks old, when they should be immune. They will still be carriers of the disease, but are not supposed to get the disease. There are numerous ongoing threads about Mareks where you can read and learn from other's experience by searching "Mareks disease" at the top of this page. Look for "The Great Big Giant Mareks Faq" for a good collection of research and info on Mareks. Googling the disease will also get you a good sampling of articles to read. Just clean your coop and equipment with some 10% bleach water, or your favorite disinfectant, as you would getting any new birds. Sorry for your loss.