December 1, 2015
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Human Immunodeficiency Virus (HIV)

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Human immunodeficiency virus (HIV) facts

  • HIV is the virus that causes HIV infection and the acquired immunodeficiency syndrome (AIDS).
  • Anal or vaginal sexual intercourse and illicit injectable drug use commonly transmit HIV. Infected mothers may also transmit HIV to their child during pregnancy or breastfeeding. Less common routes of transmission include needle-stick injuries or exposure to contaminated blood.
  • The blood supply in the United States is tested for HIV before use, and statistics show the risk of acquiring HIV infection from a transfusion is less than one in 1.5 million.
  • HIV attacks the immune system, especially cells known as CD-4 lymphocytes. Serious impairment of the CD-4 lymphocytes makes people susceptible to specific infections and cancers.
  • Untreated HIV infected progresses through three stages, with stage three being AIDS.
  • Health-care professionals diagnose HIV with tests that measure antibodies against the virus or measure the virus directly.
  • Treatment with highly active antiretroviral therapy (HAART or ART) dramatically increases life expectancy although it does not cure HIV infection.

What is the human immunodeficiency virus?

The human immunodeficiency virus is the cause of HIV infection and the acquired immunodeficiency syndrome (AIDS). HIV belongs to a family of organisms known as retroviruses. Once someone acquires the virus, it attaches to and enters human cells, especially cells known as CD4 T-cells, macrophages, and dendritic cells. The virus contains RNA, which it transcribes into DNA using an enzyme called reverse transcriptase. The resulting DNA integrates into the human genome in the cell. In this way, the virus fools the human genome into making more copies of the virus.

HIV may remain quiescent (latent) in the genome or may be actively transcribed, causing the virus to replicate. HIV is a prolific virus and is able to create trillions of copies of itself in a short period of time. During times of peak viral reproduction, even 1 milliliter of blood can contain more than 1 million copies of the virus. Many of these copies differ in small ways from the original virus and may be resistant to different medications. There are two types of HIV: HIV-1 and HIV-2. HIV-1 is the primary cause of HIV infection and AIDS in the world. HIV-2 is less common and less easily transmitted.

Medically Reviewed by a Doctor on 3/3/2014


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