Genome characterization of Salem virus reveals its evolutionary intermediate status in the subfamily Paramyxovirinae

Salem virus (SalPV) was originally isolated from a horse during a disease outbreak in 1992 in the USA. In this study, we complete the genome characterization of SalPV and confirm the classification of this virus as a member of the subfamily Paramyxovirinae. The SalPV genome is 16,698 nucleotides in length, with six transcriptional units in the order 3'-N/P/V/C-M-F-G-L-5'. SalPV has a fixed 3-nt intergenic region, which is the same as in all Paramyxovirinae members except rubulaviruses and avulaviruses. The genome size of SalPV is greater than those of the "old" members of the subfamily, such as morbilliviruses and respiroviruses, but smaller than those of the "new" members, including henipaviruses and several unclassified novel viruses. Interestingly, this evolutionary "middle point" was also reflected in the phylogeny, suggesting that SalPV represents an important intermediate between the previously well-characterized paramyxoviruses and the recently emerged members of this subfamily.