Marek's has been a much smaller "fish in our pond" than I was warned it would be. After all of the dire predictions and warnings after our first outbreak, we have not seen it. Don't get me wrong - I know it lies dormant, sometimes for years. I also still run a pretty tight ship as far as nutrition, cleanliness/antimicrobial use, and stress reduction. But, we had a very stressful summer (major wildfire, evacuations, and more) and they sailed through very well. I really do believe Marek's to be part of every poultry environment, just not in outbreak form.