HIV is the virus that causes acquired immunodeficiency syndrome (AIDS). The name stands for human immunodeficiency virus, a group of related lentiviruses that infect cells of the human immune system.
HIV primarily targets CD4 T cells, along with macrophages and dendritic cells. After entering a cell, it uses reverse transcriptase to convert its RNA genome into DNA, allowing the viral genetic material to become established inside the host cell. Over time, untreated infection can reduce CD4-cell levels and weaken immune defenses.
AIDS is not a separate virus. It is the advanced stage or clinical syndrome of HIV infection, defined by severe immune damage or particular opportunistic illnesses and cancers. Modern antiretroviral therapy can suppress HIV to very low levels and prevent progression to AIDS, although it does not routinely eliminate the virus.
A common mix-up is confusing HIV with HPV, HCV, or HBV. HPV is human papillomavirus; HCV and HBV are hepatitis C and B viruses. HIV was recognized as the cause of AIDS in the early 1980s, after AIDS itself was first reported in 1981.