The nsp 3 ORF has 43.66% of all amino acid differences observed between Ark/Ark-DPI/81 and Ark-attenuated (including a ten amino acid deletion in the attenuated virus at positions 789-798), 34.75% of all amino acid differences observed between GA98/CWL0470/98 and GA98-attenuated (including an eight amino acid deletion in the pathogenic virus at positions 901-908 and a three amino acid deletion in the pathogenic virus at positions 950-952), and 37.08% of all amino acid differences observed between Mass/Mass41/41 and Mass-attenuated (including a ten amino acid deletion in the attenuated virus at positions 797-806).