Human immunodeficiency virus (HIV) is a virus that causes acquired immunodeficiency syndrome or AIDS. AIDS is a condition in humans in which the immune system begins to fail, leading to life-threatening infections.
Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. The four major routes of transmission are unsafe sex, dirty needles, breast milk and transmission from an infected mother to her baby at birth (vertical transmission).
HIV infects about 0.6% of the world’s population. Medication reduces both the death rate and the sickness rate of HIV infection. Most people infected with HIV eventually develop AIDS. They mostly die from infections or cancers associated with the progressive failure of the immune system.
HIV progresses to AIDS at different rates; HIV-specific treatment delays this process. Most will progress to AIDS within 10 years of HIV infection: some will have progressed much sooner and some will take much longer.
Treatment with anti-retroviral medication increases the life expectancy of people infected with HIV. Even after HIV has progressed to AIDS, the average survival time with medication is estimated to be more than 5 years. Without medication, someone who has AIDS typically dies within a year.