How HIV Causes Infections
HIV transmission occurs when a person is exposed to body fluids infected with the virus, such as blood, semen, vaginal secretions, and breast milk. The primary modes of HIV transmission are (1) sexual relations with an infected person (see Sexually Transmitted Infections ); (2) sharing hypodermic needles or accidental pricking by a needle contaminated with infected blood; and (3) transfer of the virus from an infected mother to her baby during pregnancy, childbirth, or through breast-feeding. When HIV enters the body, it infects lymphocytes, which are a type of white blood cell in the immune system . HIV uses its glycoproteins to attach itself to receptors on the surface of a lymphocyte. The outer envelope of HIV then fuses with the lymphocyte, enabling the HIV capsid to enter the lymphocyte itself. HIV commandeers the genetic material of the lymphocyte, instructing the cell to replicate more viruses. The newly formed viruses break free from the host, destroying the cell in the process