ABSTRACT
Bovine coronavirus (BCoV) is associated with severe diarrhea in calves, winter dysentery in adult cattle, and respiratory diseases in cattle. However, there is limited information regarding its molecular characterization in the Republic of Korea (KOR). This study was conducted to investigate the prevalence of BCoV in diarrheic calves, perform global comparison of BCoV genome sequences, and suggest a new nomenclature. A total of 521 fecal samples were collected from diarrheic pre-weaned native Korean calves (age £60 days) from 100 herds in the KOR. The samples were divided into three groups based on age as follows: 1-21 days (n = 433), 21-40 days (n = 64), and 41-60 days (n = 24). The full-length Spike (S) gene was amplified and sequenced. The phylogenetic tree was constructed using the maximum-likelihood method and the evolutionary rates were estimated. BCoV infection was detected in 20 (3.8%) calves by real-time RT-PCR analysis, and nine full-length genome sequences were obtained from the 20 BCoV-positive samples. Genomic comparison analysis showed that these 2019-2020 variants exhibited the highest nucleotide sequence identity (98.6%-99.2%) with that of water deer (Hydropotes inermis) isolates. Phylogenetic analysis of the full genomes of the S gene revealed the following four BCoV groups: G1, classical BCoV strains; G2, 2002 Korean, Japan, Vietnam, Cuba, and USA strains/isolates; G3, European strains/isolates; and G4, Korean isolates (2004 and 2006 Korean isolates, 2010 BCoV-like, 2017 water deer, and 2019-2020 variants). The evolutionary rates accelerated from G1 to G4. This grouping was also closely related to the nucleotide substitution rate. Using molecular clock analysis of the S gene, the most recent common ancestor of each group was estimated to have originated in 1953, 1979, 1986, and 1993, respectively. Recently identified BCoV variants in the KOR are undergoing slow evolution. These findings provide useful information for understanding the molecular characterization of BCoVs. Further research is necessary to conduct recombination analysis to support BCoV evolution.