M gene analysis of canine coronavirus strains detected in Korea

Jeoung, Seok-Young; Ann, So-Yun; Kim, Hyun-Tae; Kim, Doo

Although the number of samples in our study is too small to yield firm conclusions, we provided evidence that the circulating CCVs in Korea can be divided into four Amino acids identical to those in the reference strain are indicated by dashes while amino acids different from those in the reference strain are indicated by letters. separate clusters. CCVs in cluster I had unique amino acid changes in the M protein and these isolates were very close to the CCV type II reference strains. However, these strains are divergent from the CCV type II reference strains. CCVs in cluster II were close to the CCV type II reference strains and TGEV. Members of cluster III were similar to the CCV type II reference strains and FCoV-like CCV strains, and had greater identities with the FCoV-like CCV strains than CCV type II reference strains. In another study, CCV 500 Seok-Young Jeoung et al. isolates from Austrian dogs were found to belong to both the CCV type II cluster and FCoV-like CCV cluster [4] . A phylogenic analysis by Wang et al. [34] showed that one Chinese strain belonged to a cluster between the FCoV-like CCV and CCV type II branches, suggesting the existence of a novel strain. However, Swedish CCVs were segregated into two distinct subgroups of type II CCV strains [9] . The increasing evidence suggests that recombination of coronaviruses, such as CCV and FCoV, often occur under natural conditions. The potential of interspecies circulation of either CCV in cats or FCoV in dogs is very high. And when co-infection occurs in the host, recombination can happen between two coronaviruses naturally [3, 16, 21, 26, 31] . The CCVs in cluster IV consisted of FCoV-like CCV reference strains. This result showed that there are FCoV-like CCV strains in Korea similar those described by Pratelli et al. [22, 26, 27] in Italy and Benetka et al. [4] in Austria. The FCoV-like CCV strain differs from the CCV type II strain with amino acid changes at 12 positions (Ile123Ile/Val, Val124Ile, Ile127Ala, Ser154Asn, Val173Thr, Cys187Tyr, Ile193Met, Asp200Glu, Asn201His, Val212Ser, Lys223Gln, and Asp242Gly) in the M protein [4, 25] . This finding highlights the possibility that FCoVs may be transmitted to dogs, and that there may be frequent recombination between the two types of virus [4] . Moreover, the high frequency of recombinations (in addition to small insertions and deletions) in genome containing both structural and non-structural proteins is the dominant force in the microevolution of positive RNA viruses, and results in the proliferation of different virus strains with different biological and immunological functions [6, 27] . Coronavirus genome is predicted to accumulate several base substitutions per round of replication as a result of RNA-dependent RNA polymerase errors [14, 27] . Due to the relatively high mutation frequency, CCVs have the potential to rapidly adjust to negative pressures such as those presented by the immune system [21, 25] . The possibility that the dogs might have been infected simultaneously with population of genetically distinct CCVs and that one population might have prevailed against the other during the long period of virus shedding cannot be excluded. This hypothesis could explain the stable and identical substitutions observed in the nucleotide sequences of the M gene.