Phylogenetic tree analysis of sequences of nucleocapsid (N), matrix (M), phosphoprotein (P), and non-virion protein (NV) of various IHNV strains. Information about the IHNV strains used in this analysis is described in additional file 1. IHNV 220-90 strain is marked with blue diamond. Phylogenetic tree analysis was conducted by neighbor-joining method using 1000 bootstrap replications. The scale at the bottom indicates the number of substitution events and bootstrap confidence values are shown at branch nodes.