Dear Colleagues,

With the exception of retroviruses, until very recently it was not possible to trace the evolution of currently circulating viruses further back than a few thousand years. All of this changed in the past decade with increasing availability of the genomic sequences of a variety of organisms, and new computational methods for their annotation and investigation. In the last two years, application of these methods anaalyses have uncovered genomic fossils from ancient relatives of a number of virus families with both DNA and RNA genomes, revealing some to have existed for longer than ~90 million years, the current theoretical limit of such calculations. Such revelations have raised important and fascinating new topics for inquiry: By what mechanism(s) were these viral sequences integrated into their host species genomes? What selective pressures, if any, have led to their maintenance in the host populations? What new information may be gained concerning the organization and evolution of our own genomes and those of other species in our environment?

This special issue of viruses focuses on the emerging field of Paleovirology, and will include articles that summarize the new findings and methods cited above, and well as issues related to some fundamental questions now open for consideration. The search for answers and new knowledge obtained is sure to increase our understanding of both virus and host biology and evolution in the future.

Prof. Dr. Anna Marie Skalka
Guest Editor

• virus fossils
• LINE-facilitated integration
• intrinsic resistance
• virus reservoir species
• selective pressures
• genomic analyses