the virus. in the toroviruses, the berne virus has been extensively studied at the molecular level as compared to its other members. in 1992, the international committee on taxonomy of viruses ictv got enough data to consider torovirus in the coronavirus family due to the similarities in structure, replication behavior and the genetic sequencing. evolution toroviruses, coronaviruses and arteriviruses are in the order nidovirales, a group of non segmented, positive sense single stranded animal viruses. despite the differences in their genome size, varying host range and their replication strategies, the similarities in the sequence identities of the replicase proteins among different species of order nidovirales ensures their common ancestry. sequence analysis and comparison of the polymerase and helicase domains of coronaviruses and toroviruses reveled 40-45% identical amino acids in both families, providing evidences of large evolutionary distance between the two families.