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.

During the 41st Chinese Antarctic Expedition (2024–2025), fresh faecal samples were collected from sympatric Adélie, chinstrap, and gentoo penguins on Ardley Island. The faecal viromes were systematically profiled via transcriptomic sequencing coupled with viral contig assembly. Thirty-two known viral families were annotated, yet over half of viral reads remained unclassified, indicating substantial uncharacterised viral diversity in Antarctic penguin guts. No significant interspecific differences in viral abundance or alpha-diversity were detected, and host-species exerted only a weak effect on viral community structure. While H5N1 highly pathogenic avian influenza and Newcastle disease virus were absent, several potential pathogens, including deltacoronaviruses, novel astroviruses, and picornaviruses, were recovered. This work establishes baseline virome data for Antarctic pygoscelid penguins and provides valuable insights for long-term pathogen surveillance of polar wildlife and assessments of viral spillover risk.