English: Maximum likelihood phylogeny of 24 complete genome sequences of MYXV. Viruses are color- coded according to virulence grade.

• Grade 1: Case fatality rate: 99.5% Average survival time: less than 13 days
• Grade 2: Case fatality rate: 95-99% Average survival time: 14-16 days
• Grade 3: Case fatality rate: 70-95% Average survival time: 17-28 days
• Grade 4: Case fatality rate: 50-70% Average survival time: 29-50 days
• Grade 5: Case fatality rate: less than 50% Average survival time: not defined.

• Grade 1 = red
• Grades 3–4 = green
• Grade 5 = blue

The tree is rooted between the two oldest strains in the collection – Lausanne (1949) and SLS (1950) – which were used to seed the European and Australian epidemics, respectively (marked by asterisks).