The virosphere is all those places where viruses are found or in which they interact with their hosts. It has also been spelled as viriosphere, though this is less common and seems to have been supplanted by the other form.
Its appearance shows how scientists are coming to realise that the viruses are not mere causes of disease and parasitic nuisances on the fringes of life but a key part of the living world. Vastly more virus species exist than previously thought (100 million or more, outnumbering any other type of organism) and they are to be found in pretty much every environment on the planet. They contain more genetic material than the rest of life, so much of it unique that it’s no longer possible to dismiss them as a irrelevant aside but a separate class of biological existence that may be even older than bacteria. A significant part of the human genome turns out to consist of viral genes and it is beginning to look as though the ability of viruses to transfer genes to and from their hosts and each other — so spreading genes throughout the biological world — may have been an important factor in the evolution of species.
The term appeared no later than 1997 in a poster issued by the International Committee on Taxonomy of Viruses, in the slightly different sense of the diversity of virus types. Professor Curtis Suttle of the University of British Columbia used it in the current sense (but spelled viriosphere) in the journal Environmental Microbiology in 2005 and its current usage dates from that. It remains uncommon, even in scientific literature, but a few straws in the wind suggest it is becoming a standard term.
The need to periodically update the classification schemes testifies to the dynamic nature of the “virosphere”.
Animal Viruses, by Thomas C Mettenleiter and Francisco Sobrino, 2008
Only three of these systems survive to this day in the form of the three domains of cellular life; much of the rest lives on the virosphere.
New Scientist, 30 Aug. 2008