Identification and genomic characterization of emerging CRESS DNA viruses in thoroughbred horses in China

Multiple novel circular replication-associated protein (Rep)-encoding single stranded (CRESS) DNA viruses have been extensively identified in the feces of humans and animals. Here, we first detected CRESS DNA virus (named Horse-CRESS DNA-like virus, HCLV) in two fecal samples from 10 imported thoroughbred (TB) horses in the customs quarantine station in North Xinjiang province, China. Additionally, we found that this virus was not detected in local breeds (LBs) (0/41) and was found only in imported TB horses (2/73). We obtained the whole-genome sequences of four viruses (HCLV ALSK-3-4, ALSK-13-10, CJ-1-2, and CJ-13-1). Unlike Circovirus and Cyclovirus, whose genome sequences have 1700 to 2100 nucleotides (nt), these HCLVs have circular genome with 3503, 3504, 3485, 3491 nt, respectively and five major ORFs. The ORF1 gene encodes the Rep protein in HCLVs. Furthermore, the Rep protein of the four HCLVs share 23.3-84.8%, 21.6-27.4%, 23.7-27.2% amino acid identity with the corresponding reference viruses of Kirkoviruses, genus Circovirus, and genus Cyclovirus, respectively. Moreover, RCR domain, P-loop NTPase domains, and nonanucleotide motif (TAGTATTAC) of the HCLVs are similar to Circovirus and Cyclovirus. Phylogenetic analysis showed that the virus was grouped together with members in Kirkoviruses. These results suggest the HCLV probably entered Xinjiang province via the international trade of horses.