Marek’s disease can wreck a chicken flock fast, causing tumors, paralysis, and then death in 100 percent of cases in organic chicken farms that refuse to accept vaccines. Yet it can wreck a chicken flock fast, causing tumors, paralysis, and then death in 100 percent of cases in organic chicken farms that refuse to accept vaccines. Their effort involved 65 Marek's disease virus (Mardivirus gallidalpha2) strains stored by the U.S. Department of Agriculture since the 1960s. A map of all ORFs in the MDV genome is shown below the x axis, with ORFs associated with genome-wide significant variants shown in color. The authors are particularly interested in a DNA variant where a segment of DNA gets duplicated - a tandem repeat - and intend to focus on that next.