Emergence of a Novel CRESS-DNA Virus Associated with Swine Reproductive Failure in China

The continuous emergence of circular Rep-encoding single-stranded (CRESS) DNA viruses across diverse hosts has been closely associated with the occurrence of severe diseases. Four circoviruses within the genus Circovirus have been identified in pigs, including porcine circovirus Type 1 (PCV1), PCV2, PCV3, PCV4, and PCV5. In late 2021, a large pig farm experienced an outbreak of reproductive disorders that were undiagnosed by standard tests. Subsequent viral metagenomic analysis of stillborn piglets identified a novel single-stranded circular DNA virus, designated porcine megalocircovirus (PMCV). PMCV has a large genome of 9426 nt and encodes nine open reading frames. Biochemical analyses of Rep confirm PMCV as a CRESS DNA virus. However, PMCV Rep showed low amino acid sequence identities to the four PCV species and several human CRESS DNA viruses, with the highest identity of 23.6% to PCV4 Rep. The genetic evolutionary tree indicates that PMCV belongs to an unknown family of the CRESS DNA viruses. The positive detection rate for PMCV in tested samples was 24% (30/125), while the positive rate regarding pig farms was 41.18% (14/34) in China. The emergence of PMCV warrants further investigation.