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What
is HIV?
HIV (human immunodeficiency virus) weakens the body's
immune defenses by destroying CD4 (T-cell) lymphocytes.
CD4 lymphocytes are a group of white blood cells
that normally help guard against attacks by bacteria,
viruses and other germs by coordinating the immune
system. When HIV destroys CD4 lymphocytes, the body
becomes vulnerable to many different types of opportunistic
infections (infections that have an "opportunity"
to invade the body because its immune defenses are
weak). HIV infection also increases the risk of
certain malignancies (cancers), neurologic illnesses
(illnesses of the brain and nerves), body wasting
and death. The entire spectrum of symptoms and illnesses
that can happen when HIV infection significantly
depletes immune defenses is called AIDS (acquired
immunodeficiency syndrome).
Since 1981, when HIV/AIDS was first recognized
as a new illness, scientists have learned much
about the HIV infection process. HIV is spread
through contact with an infected person's body
fluids, especially through blood, semen and vaginal
fluids. Once inside the body, HIV viral particles
attach to CD4 lymphocytes and use a series of
chemicals, including viral RNA (ribonucleic acid)
and viral proteins, to turn the CD4 lymphocytes
into viral factories. When this happens, infected
CD4 cells devote their energy to manufacturing
new HIV particles rather than to protecting the
body. As newly manufactured HIV particles enter
the bloodstream, they infect more CD4 cells, which
produce even more HIV particles. In this way,
the cycle of HIV infection continues, and the
number of infected CD4 lymphocytes increases.
Eventually, HIV destroys the infected CD4 lymphocytes,
and as CD4 numbers drop, the body's immune defenses
weaken. In addition, HIV may also remain "silent"
as a latent (dormant) infection in some CD4 cells,
only to awaken and spread after long periods of
inactivity.
Within the past two decades, more than 400 million
people worldwide have become infected with HIV,
and approximately 12 million have died. As of
mid-1997, there had been more than 612,000 cases
of AIDS reported in the United States, with almost
380,000 deaths, including 4,600 children.
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