The Human Immunodeficiency Virus (HIV) is a virus which attacks the T-cells in the immune system. Acquired Immune Deficiency Syndrome (AIDS) is a syndrome which appears in advanced stages of HIV infection. The difference between HIV and AIDS is that HIV is a virus, while AIDS is a medical condition. HIV is sometimes referred to as the causative agent, since it is not possible to develop AIDS without an HIV infection, although it is possible to be infected with HIV without developing AIDS.
HIV can be transmitted sexually or through blood products. Some common risk factors for HIV infection include: unprotected sex, needle sharing, and exposure to contaminated blood products. Once someone is infected with HIV, the virus begins to replicate in the blood, slowly hijacking the T-cells so that they cannot function normally. If the infection is allowed to progress, eventually it will develop into AIDS. People with HIV and AIDS are at increased risk of opportunistic infections, because their immune systems are weakened.
AIDS is characterized by infection with HIV and the presence of one or more opportunistic infections. Toxoplasmosis, uncontrollable candida infections, cytomegalovirus, pneumocystitis pneumonia, and Kaposi's Sarcoma are some examples of AIDS-associated infections. In tests of the patient's blood, the number of T-cells is drastically below normal readings, reflecting the weakened state of the immune system. The HIV virus in an AIDS patient's body is also still present and still infectious, and someone with AIDS can pass HIV to someone else.
One could think of the difference between HIV and AIDS in the sense that HIV is a virus, while AIDS is a disorder, much like Toxic Shock Syndrome (TSS) is a disorder which is caused by infection with staph bacteria. Progression of viral infection to full-blown AIDS is very undesirable, as the opportunistic infections which set in can kill the patient. Routine HIV testing can identify infection in the early stages, allowing the patient to use prophylactic drugs which will slow the rate of replication for the virus, delaying the onset of AIDS.
The line between HIV and AIDS has been blurred in the popular media, which can be confusing for lay people. Many clinics, for example, advertise “free AIDS tests” to their clients, when in fact they mean “free HIV tests.” Both HIV and AIDS are also the subject of a great deal of research in the scientific community, with doctors looking for new treatment approaches to early stages of HIV infection as well as AIDS itself.