An adagio for viruses, played out on ancient DNA.

Studies of ancient DNA have transformed our understanding of human evolution. Palaeogenomics can also reveal historic and prehistoric agents of disease, including endemic, epidemic and pandemic pathogens. Viruses - and in particular those with single or double-stranded DNA genomes - are an important part of the palaeogenomic revolution, preserving within some remains or environmental samples for tens of thousands of years. The results of these studies capture the public imagination, as well as giving scientists a unique perspective on some of the more slowly-evolving viruses which cause disease. In this review, we will revisit the first studies of historical virus genetic material in the 1990s, through to the genomic revolution of recent years. We will look at how palaeogenomics works for viral pathogens, such as the need for careful precautions against modern contamination, and robust computational pipelines to identify and analyse authenticated viral sequences. We will discuss the insights into virus evolution which have been gained through palaeogenomics, concentrating on three DNA viruses in particular: parvovirus B19, herpes simplex virus 1, and smallpox. As we consider recent worldwide transmission of monkeypox and synthetic biology tools that allow the potential reconstruction of extinct viruses, we show that studying historical and ancient virus evolution has never been more topical.