Esteban and Hutchinson BMC Genomics 2011, 12:261 http://www.biomedcentral.com/1471-2164/12/261 Authors’ contributions DJE conceived of the study, participated in its design and coordination, carried out the analysis and drafted the manuscript. APH participated in the design of the study, carried out the analysis, and helped to draft the manuscript. All authors have read and approved the final manuscript. Received: 9 July 2010 Accepted: 23 May 2011 Published: 23 May 2011 References 1. Moss B: Poxviridae: The Viruses and Their Replication. In Fields Virology.. 5 edition. Edited by: Knipe DM,Howley PM,Griffin DG, et al. Philadelphia: Lippincott Williams 2007:. 2. Upton C, Slack S, Hunter AL, Ehlers A, Roper RL: Poxvirus orthologous clusters: toward defining the minimum essential poxvirus genome. J Virol 2003, 77(13):7590-600. 3. Gubser C, Hué S, Kellam P, Smith GL: Poxvirus genomes: A phylogenetic analysis. J Gen Virol 2004, 85(1):105-117. 4. 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