Genome sequence and comparative virulence of raccoonpox virus: the first North American poxvirus sequence

We report here the complete genome sequence of raccoonpox virus (RCNV), a naturally occurring North American poxvirus. This is the first such North American sequence to the best of our knowledge, and the data showed that RCNV forms a new phylogenetic branch between orthopoxviruses and Yoka poxvirus. RCNV shared overall similarity in genome organization with orthopoxviruses, and the proteins in the central conserved region shared approximately 90  % amino acid identity with orthopoxviruses. RCNV proteins shared approximately 81  % amino acid identity with Yokapox virus proteins. RCNV is missing 10 genes normally conserved in orthopoxviruses, most of which are implicated in virulence. These gene deletions may explain the attenuated phenotype of RCNV in mammals. RCNV contained one unique genome region containing approximately 1 kb of DNA sequence that is not present in any reported poxvirus. It contained a unique ORF predicted to encode a protein with a transmembrane domain. RCNV replicates well in mammalian cells, is naturally attenuated and has been shown to be effective as a vaccine vector platform, so we further tested its safety. We showed here that RCNV is substantially more attenuated than even the highly attenuated VACV-A35Del mutant virus in pregnant, nude and severe combined immunodeficient (SCID) mouse models. RCNV was much safer in pregnant mice and was cleared rapidly from tissues, even in immunocompromised animals, whereas the VACV-A35Del mutant retains virulence and persists in tissues. Thus, RCNV is expected to be a superior vaccine vector for infectious diseases and cancer due to its excellent safety profile, reported vaccine efficacy and ability to replicate in mammalian cells.