Acquired immunodeficiency syndrome
Classification and external resources
The Red ribbon is a symbol for solidarity with HIV-
positive people and those living with AIDS.
List of abbreviations used in this article
AIDS: Acquired immune deficiency syn-
HIV: Human immunodeficiency virus
CD4+: CD4+ T helper cells
CCR5: Chemokine (C-C motif) receptor 5
CDC: Centers for Disease Control and Pre-
WHO: World Health Organization
PCP: Pneumocystis pneumonia
MTCT: Mother-to-child transmission
HAART: Highly active antiretroviral ther-
STI/STD: Sexually transmitted infec-
Acquired immune deficiency syndrome or
(AIDS) is a disease of the human immune
system caused by the human immunodefi-
ciency virus (HIV).
This condition progressively reduces the
effectiveness of the immune system and
leaves individuals susceptible to opportunist-
ic infections and tumors. HIV is transmitted
through direct contact of a mucous mem-
brane or the bloodstream with a bodily fluid
containing HIV, such as blood, semen, vagin-
This transmission can involve anal, vaginal
or oral sex, blood transfusion, contaminated
mother and baby during pregnancy, child-
birth, or breastfeeding, or other exposure to
one of the above bodily fluids.
AIDS is now a pandemic. In 2007, it was
estimated that 33.2 million people lived with
the disease worldwide, and that AIDS had
killed an estimated 2.1 million people, includ-
ing 330,000 children. Over three-quarters
of these deaths occurred in sub-Saharan
Africa, retarding economic growth and des-
troying human capital.
Genetic research indicates that HIV ori-
ginated in west-central Africa during the late
nineteenth or early twentieth century.
AIDS was first recognized by the U.S.
Centers for Disease Control and Prevention