Acquired immune deficiency syndrome, or AIDS, is a
disease entity that has been recognized since 1981. It is caused by
infection with the human immunodeficiency virus, which attacks
selected cells in the immune system and produces defects in
function. This leaves the body open to an invasion by various
infections, which are therefore called opportunistic diseases, and
to the development of unusual cancers. The virus also tends to
reach certain brain cells. Since the first AIDS cases were
reported in 1981, through mid-1991, more than 190,000 AIDS
cases and more than 120,000 deaths had been reported in about
162 countries worldwide. Sub-Saharan Africa in particular
appears to suffer a heavy Berden of this illness.
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