The Human Immunodeficiency Virus (HIV) targets the immune system and weakens people's defence systems against infections and some types of cancer.
HIV is a blood-borne virus typically transmitted via sexual intercourse, shared intravenous drug paraphernalia, and mother-to-child transmission, which can occur during the birth process or during breastfeeding.
HIV disease is caused by infection with HIV-1 or HIV-2, which are retroviruses in the Retroviridae family, Lentivirus genus.
As the virus destroys and impairs the function of immune cells, infected individuals gradually become immunodeficient. Immune function is typically measured by CD4 cell count. Immunodeficiency results in increased susceptibility to a wide range of infections and diseases that people with healthy immune systems can fight off.
The most advanced stage of HIV infection is Acquired Immunodeficiency Syndrome (AIDS), which can take from 2 to 15 years to develop depending on the individual. AIDS is defined by the development of certain cancers, infections, or other severe clinical manifestations.

Key facts

HIV continues to be a major global public health issue, having claimed more than 34 million lives so far. In 2014, 1.2 [980,000–1.6 million] million people died from HIV-related causes globally.

There were approximately 36.9 [34.3–41.4] million people living with HIV at the end of 2014 with 2.0 [1.9–2.2] million people becoming newly infected with HIV in 2014 globally.
Sub-Saharan Africa is the most affected region, with 25.8 [24.0–28.7] million people living with HIV in 2014. Sub-Saharan Africa accounts for almost 70% of the global total of new HIV infections.

HIV infection is often diagnosed through rapid diagnostic tests (RDTs), which detect the presence or absence of HIV antibodies. Most often these tests provide same-day test results; essential for same-day diagnosis and early treatment and care.

There is no cure for HIV infection. However, effective antiretroviral (ARV) drugs can control the virus and help prevent transmission so that people with HIV, and those at substantial risk, can enjoy healthy and productive lives.

It is estimated that currently only 54% of people with HIV know their status. In 2014, approximately 150 million children and adults in 129 low- and middle-income countries received HIV testing services.

By mid-2015, 15.8 million people living with HIV were receiving antiretroviral therapy (ART) globally.

Between 2000 and 2015, new HIV infections fell by 35%, AIDS-related deaths fell by 24% with some 7.8 million lives saved as a result of international efforts such as the United Nations' Millennium Development Goals, which included halting the spread of HIV.

Expanding ART to all people living with HIV and expanding prevention choices can help avert 21 million AIDS-related deaths and 28 million new infections by 2030.

See reference for details.

World Health Organization. HIV/AIDS Fact sheet N°360 updated November 2015. Internet. Accessed January 25, 2016.