- In full:
- human immunodeficiency virus
HIV
What is HIV?
What are the two types of HIV and how do they differ?
How is HIV transmitted?
Who discovered HIV and when?
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HIV, retrovirus (family Retroviridae) that attacks and progressively weakens the immune system by targeting cells that help the body fight infection.
HIV is more specifically classified as a lentivirus, or “slow virus,” because disease progression can occur over many years. If left untreated HIV can severely damage immune function. The most advanced stage of infection is acquired immunodeficiency syndrome (AIDS). Although there is currently no cure for HIV infection, antiretroviral therapy (ART) can suppress the virus, allowing many people with HIV to live long, healthy lives.
Types and replication
HIV occurs in two principal forms, HIV-1 and HIV-2, which differ substantially in their genetic makeup and originated from different simian immunodeficiency viruses (SIVs) in African primates. HIV-1 is more transmissible and accounts for most infections worldwide, whereas HIV-2 is found primarily in western Africa and generally causes slower disease progression.
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Both types of HIV contain a genome composed of two copies of single-stranded RNA enclosed within a protein capsid and a lipid envelope. Embedded in the viral envelope are proteins that enable the virus to attach to and enter host cells, particularly CD4 T cells (helper T cells), a type of white blood cell that plays a central role in immune function. Once inside a host cell, HIV uses an enzyme called reverse transcriptase to convert its RNA into DNA. A second enzyme, integrase, inserts the viral DNA into the host cell’s genome, where it may remain dormant or direct the production of new viruses. Newly formed viral particles are assembled within the cell and released to infect additional cells. HIV replication is aided by another viral enzyme, protease, which helps produce mature, infectious virus particles.
Transmission and disease progression
HIV is transmitted through contact with certain bodily fluids, including blood, breast milk, semen, and vaginal or rectal fluids. The virus is spread primarily by unprotected sexual contact, sharing contaminated needles or syringes, and transmission from parent to child during pregnancy, childbirth, or breastfeeding. HIV is not spread through casual contact such as hugging or shaking hands.
HIV infection generally progresses through several stages. Shortly after infection some individuals experience an acute phase marked by flu-like symptoms, including fever, fatigue, sore throat, and swollen lymph nodes. This stage is followed by a prolonged period known as clinical latency, during which the virus remains active but may cause few or no symptoms. Over time untreated HIV gradually reduces the number of CD4 T cells, weakening the immune system. As immune function declines infected individuals become increasingly vulnerable to opportunistic infections and certain cancers. When immune damage becomes severe, HIV infection progresses to AIDS, which is characterized by profound immune deficiency and life-threatening complications.
Discovery
French virologists Luc Montagnier and Françoise Barré-Sinoussi identified HIV in 1983 while investigating the cause of AIDS, a disease that had begun to draw international attention after unusual clusters of rare infections and cancers were reported among previously healthy individuals in the United States in 1981. In 1984 American scientist Robert Gallo definitively proved that HIV is the cause of AIDS. Subsequent research traced the virus’s origins to SIVs carried by African primates, from which HIV emerged through cross-species transmission.
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Throughout the 1980s and ’90s HIV spread globally and became one of the most significant public health challenges of the modern era. The introduction of combination antiretroviral therapy in the mid-1990s dramatically improved survival rates and transformed the management of HIV infection. Despite major advances in treatment and prevention, nearly 41 million people worldwide live with HIV, and the virus remains an important focus of medical research and public health efforts.
For additional information on HIV, see AIDS.