Bayesian Inference (BI) p4c phylogeny with ECTV as outgroup taxa. The BI tree was constructed with Mr Bayes 3.1.2 as detailed in Methods. Posterior probabilities are shown on the right side of each node. The scale bar represents expected substitutions per site. The topology of phylogenetic trees constructed with Neighbor Joining (NJ) method as implemented in MEGA 5.0.5 was similar to the BI and ML trees. CPXVs (14 in total) belonging to clusters (groups) 1 to 5 are CPXV-like because the 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).