The p4c gene Maximum Likelihood (ML) phylogenetic tree with CPXV-No-H2 as outgroup. The ML tree was constructed with MEGA 5.05 as outlined in Methods. ECTV sequences were excluded from the analysis. Bootstrap analysis with 1000 replicates was performed and only bootstrap values above 70% are shown. The scale represents substitutions per site. Neighbor Joining (NJ) tree and Bayesian Inference (BI) trees constructed with MEGA 5.05 and Mr Bayes 3.1.2 have tree topologies similar to the ML tree generated with MEGA 5.05. CPXVs (14 in total) belonging to clusters (groups) 1 to 5 are CPXV-like because they descended from the same common ancestor as the reference strain CPX-BR. CPXV groups 6 and 7 (4 viruses in total) are VACV-like because they are closer to VACV than CPXV-like viruses (groups 1 to 5). CPXV group 7 and VACV share a common ancestor.