Comparative Genomics Analysis between frog Virus 3-like Ranavirus from the First Canadian Reptile Mortality Event and Similar Viruses from Amphibians

Ranaviruses are emerging pathogens that threaten the biodiversity of wild and captive cold-blooded vertebrates. Reports of ranavirus-induced mortality events are increasing and ranavirus disease is reportable to the World Organization for Animal Health. Previous studies have suggested interclass transmission of ranaviruses and Frog virus 3 (FV3)-like viruses are of particular interest. This study presents the whole-genome assembly of a 106 kb FV3-like genome obtained from the liver tissue of a reptile (wild Chelydra serpentina, common snapping turtle) that died of ranavirus disease in Canada. The FV3-like ON turtle/2018 strain shares the highest genome-wide nucleotide identity (99.71%) with the wild-type FV3 virus detected in the USA from a Northern leopard frog and an FV3-like strain identified from a wood frog in 2017 in Alberta, Canada. The novel genome contains all 26 Iridoviridae core genes, 11 FV3-like genes, and 9 unique truncations, three of which are core Iridoviridae ORFs. Additionally, the two most closely related FV3-like strains from amphibians, were compared to a non-FV3-like amphibian infecting and a fish infecting ranavirus species that showed similar codon usage patterns. G/C-ending codons were the preferred codons for all five strains. Investigation of putative recombination events identified four potential recombination events in the FV3-like ON turtle/2018 genome consistent with this FV3-like reptile infecting strain originating from an amphibian infecting FV3-like ranavirus. Altogether, this study provides insights into the genome structure and the differences in the novel FV3-like genome compared to other ranavirus genomes.