Human immunodeficiency virus (HIV) is a virus that attacks the white blood cells called helper T cells (CD4). These cells are part of the immune system. They fight off infections and disease. As a result, an HIV infection can leave you vulnerable to severe illnesses.

AIDS is a late stage of HIV infection. It reflects severe damage to the immune system. One or more opportunistic infections will also likely exist. Opportunistic infections are a type of infection that only occur in people with compromised immune systems.

HIV is spread through contact with HIV-infected blood or other body fluids. This includes semen, vaginal fluid, and breast milk. The infection may be the result of HIV-1 or HIV-2 virus.

AIDS is caused by the destruction of T cells. The destruction is caused by the HIV virus.

Immune System
Immune system white blood cell
HIV destroys white blood cells vital to the immune system.
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HIV is most commonly spread through:

  • Sexual contact with an HIV-infected person, especially vaginal or anal sex
  • Transfer of HIV from a mother to child during pregnancy, childbirth, or breastfeeding
  • Using an HIV-contaminated needle

Rarely, HIV can be spread through:

  • A blood transfusion with HIV-infected blood
  • Blood from an HIV-infected person getting into an open wound of another person
  • Being bitten by someone infected with HIV
  • Sharing personal hygiene items with an HIV-infected person