Human Immunodeficiency Virus

The Human Immunodeficiency Virus is a chronic disease that gradually weakens the immune system by disabling and killing "T-helper ", which normally signal other constituents of the immune system to perform their respective roles. When HIV reduces the number of T-helper cells below a certain threshold, an infected person is vulnerable to opportunistic infections and cancers that typify Acquired ImmunoDeficiency Syndrome, or AIDS. It is transmitted primarily through sexual contact with an infected person, sharing of needles or syringes, and, less frequently, through transfusion of infected blood or blood clotting factors. .

HIV is a retrovirus, and integrates its genetic information into the host cell's genome.