Chelsea House, 2012. - 139 p. - No one knows the origins of
viruses. They have been on Earth for so long that it is believed
that they may predate the first living cells. Today, viruses are
found around the world, infecting bacteria and the cells of plants,
fungi, animals, and humans. Viruses are parasites that cannot copy
themselves and must invade other forms of life to reproduce. As
they invade, viruses can inflict fatal diseases and transform
normal cells into tumor cells. In Viruses, examine the life cycles
of these tiny parasites, the ways they affect their hosts, and the
ways that their ability to mutate present an ongoing challenge to
the medical community.