Identification and phylogenetic analysis of Korean frog virus 3 (FV3)-like ranaviruses through whole-genome sequencing.

Infectious diseases, particularly those caused by members of the genus Ranavirus (Iridoviridae), have caused mass mortality events in amphibian populations worldwide. Frog virus 3 (FV3) infects a wide range of amphibian hosts and results in high mortality. Despite the global prevalence of FV3, its origin and routes of spread remain unclear, largely because of limited genetic data from limited geographic regions. This study aimed to classify the ranaviruses isolated in the Republic of Korea through whole-genome sequencing. We collected amphibian carcasses and both symptomatic and asymptomatic live amphibians. The asymptomatic amphibians were collected from locations with previous infections. Among the 278 amphibian samples collected from 24 locations, 44 were positive for ranavirus according to quantitative PCR (qPCR) analysis. We obtained whole-genome sequences from 5 isolates, all of which were identified as FV3-like ranaviruses and belonged to the Asian FV3 clade in the maximum likelihood phylogenetic tree. By comparative analysis of open reading frames (ORFs) and phylogenomic trees, the Korean isolates were further divided into 2 strains: FV3-Kor_MT (mountain lineage) and FV3-Kor_LL (lowland lineage). Our findings highlight the importance of surveillance of a wide range of amphibian species and facilitate phylogenetic analyses of global FV3-like strains, including newly verified Korean strains.