Viral surveillance of invasive mammals in New Zealand reveals unique viral lineages reflecting their introduction history.

Introduced mammalian species in Aotearoa New Zealand pose significant ecological risks and may serve as reservoirs for novel or emerging infectious diseases. In this study, we present the first metatranscriptomic survey of viruses in five introduced mammals: ferrets (Mustela furo), stoats (Mustela erminea), weasels (Mustela nivalis), brushtail possums (Trichosurus vulpecula), and European hedgehogs (Erinaceus europaeus), sampled across both the North and South Islands. Through total RNA sequencing, we identified 11 mammalian-infecting viruses spanning eight viral families, including four novel virus species: Ferret mastadenovirus, Possum astrovirus, Ferret pestivirus, and Weasel jeilongvirus. Whole genomes were recovered for six of these viruses, enabling detailed phylogenetic analysis. Notably, we observed strong global geographic clustering in both Wobbly possum disease virus and Ferret hepatitis E virus, suggesting localized viral evolution following the introduction of their hosts into New Zealand. In addition, the detection of Human rotavirus A in hedgehogs highlights the possibility of reverse zoonotic transmission. Together, these findings broaden our understanding of the viral diversity harbored by New Zealand's introduced mammals and provide a critical foundation for future biocontrol and disease surveillance efforts.IMPORTANCEIntroduced mammals in Aotearoa New Zealand not only threaten native biodiversity through predation and competition, but also represent a largely overlooked source of infectious disease risk. Viruses circulating in these species may spill over into native wildlife, livestock, or even humans, while human viruses can also establish in introduced animals and create new reservoirs. Understanding which viruses are present, and how they evolve in isolated host populations, is critical for anticipating future disease outbreaks, improving biosecurity, and guiding wildlife management strategies. This work provides foundational knowledge that links ecology, conservation, and health, highlighting the need to consider pathogens as part of the broader impact of invasive species.