1. Introduction
With the explosion of sequencing technology and development of bioinformatic tools, an eruption in the number of novel microorganisms, especially viruses, were discovered in a variety of sample types (Mokili, Rohwer, & Dutilh, 2012; Tisza et al., 2020). In the field of veterinary medicine, since the detection of a closed circular single-stranded DNA virus (porcine circovirus, PCV) (Tischer, Gelderblom, Vettermann, & Koch, 1982), four circular DNA viruses were detected from clinically diseased pigs, including PCV2 (Meehan et al., 1998), P1 (Wen et al., 2012), PCV3 (Palinski et al., 2017) and the most recent PCV4 (Zhang et al., 2020). Up to date, by reverse genetics, the genomic clones of PCV2, P1 and PCV3 were demonstrated to be infectious and were able to induce gross and histopathological lesions in experiment specific pathogen free or conventional pigs (Fenaux et al., 2002; Jiang et al., 2019; Wen et al., 2012). Despite that, only PCV2 is widely acknowledged as an primary causative agent of porcine circovirus‐associated diseases (Opriessnig, Meng, & Halbur, 2007; Segales, 2012).
Of the 2 viruses most recently described, PCV3 and PCV4 viruses, PCV3 was widely detected in Asia (Kedkovid et al., 2018; D. Zhao et al., 2018), Europe (Faccini et al., 2017; Franzo et al., 2018) and America (Arruda et al., 2019; Tochetto et al., 2018). In contrast, to date, PCV4 were reported in China (Tian et al., 2020; Zhang et al., 2020) but none were detected in retrospective samples collected from 1997- 2018 in Spain and Italy (Franzo et al., 2020). In order to contribute to the understanding of geographic distribution and genomic structure of this novel virus, this study firstly performed molecular based screening for the presence of PCV4 in Korea from tissue samples collected from August 2019 to August 2020. Upon having complete genomic sequence of PCV4, a wide range of bioinformatic tools were utilized to investigate the potential biological important proteins encoded by PCV4 which might play roles in the replication process and/or pathogenesis of PCV4 in pigs.