is an annoying little bug. Although most people who get it are fine,
four percent get sick with everything from leukemia to lower limb
paralyses, arthritis and uveitis, an inflammation of the iris.
basic viruses are tiny intracellular parasites whose sole purpose
is to invade the cells of other organisms - like yours, for instance
- and make copies of themselves. Scientists debate whether viruses
are alive or whether they're just molecules capable of reproduction
under specific conditions, like microscopic Xerox machines that
need your DNA to work.
viruses make people sick in a variety of ways: destroying the cells
they have invaded; whipping up the immune system into a frenzy of
fevers, fatigue, and other symptoms or by jury-rigging the DNA of
their host's chromosomes.
specialty is retroviruses, which reproduce by making DNA from RNA
using an enzyme called reverse transcriptase. Because they make
DNA retroviruses can integrate into their host's DNA, sometimes
(as in the case of HIV) lying dormant for years.
is one of three viruses that have since been linked to cancer in
humans. The others are human papilloma virus, which causes cervical
cancer, and hepatitis C virus, which causes liver cancer.
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