The Spleen Viromes of Australia’s Endemic Platypus are Dominated by Highly Diverse Papillomaviruses

The platypus (Ornithorhynchus anatinus), a unique monotreme, represents a pivotal point in mammalian evolution, with its distinctive traits, such as electroreception and venom production. Despite its evolutionary significance, the viral diversity within platypuses remains poorly understood. This study employed next-generation sequencing to investigate the virome of the dead platypuses, uncovering a range of novel and divergent viruses. Among the identified viruses were four complete genomes of papillomaviruses (OaPV1–4) exhibiting substantial divergence from known strains, suggesting a novel genus within the subfamily Secondpapillomavirinae. Additionally, five novel parvoviruses were detected, including two with complete genomes, highlighting the complex viral ecosystem of the platypus. Phylogenetic analysis placed these viruses in unique evolutionary branches, further demonstrating the platypus’s evolutionary significance. A circular DNA virus, a tombus-like virus, and a Nodamuvirus were also identified, expanding the understanding of viral diversity in monotremes. These findings offer crucial insights into viral evolution in one of the most unique mammalian lineages, emphasising the need for further exploration to assess ecological and pathological impacts on platypus populations.