What are HIV and AIDS?

The human immunodeficiency virus, or HIV, attacks the body's immune system. By weakening the body's defences against disease, HIV makes the body vulnerable to a number of potentially life-threatening infections and cancers. HIV is infectious, which means it can be transmitted from one person to another.

HIV infects cells that are part of the body's immune system. As more cells are infected by the virus, the immune system becomes less able to fight off disease.

To productively infect a cell, HIV must introduce its genetic material into the interior of the cell. This process begins with attachment and entry of the virus, uncoating of the virus membrane and integration of the virus genes into the human gene. The human cell is hijacked to manufacture viral building blocks for multiple copies that are subsequently assembled, eventually breaking out of the infected cell in search of other cells to infect. The virus kills the cells it infects and also kills uninfected bystander cells. The virus ensures that the human cell survives until its own multiplication is completed. Even more damaging, HIV establishes stable dormant forms that are reservoirs of infection that cannot be reached by currently available drugs. These reservoirs make complete eradication-and a cure for AIDS-a challenge.

Soon after HIV infection occurs, the body's immune system mounts an attack against the virus by means of specialized killer cells and soluble proteins called antibodies that usually succeed in temporarily lowering the amount of virus in the blood. HIV still remains active, though, continuing to infect and kill vital cells of the immune system. Over time, viral activity significantly increases, eventually overwhelming the body's ability to fight off disease.

If left untreated, HIV will almost always deplete the immune system. This leaves the body vulnerable to one or more life-threatening diseases that normally do not affect healthy people. This stage of HIV infection is called AIDS, or acquired immunodeficiency syndrome. The more the immune system has been damaged, the greater the risk of death from opportunistic infections.

Experts agreed on the term 'AIDS' in the early 1980s, before the discovery of HIV, to describe the then-new syndrome of profound immune suppression. Today, AIDS is understood as the latter stage along a continuum of HIV infection and disease.

In the absence of treatment, HIV generally takes 8 to 10 years to progress to AIDS. The interval between initial infection and the appearance of symptoms, however, varies and appears to be shorter for persons infected through blood transfusion and for paediatric patients. Factors that alter the natural history of HIV infection are termed 'cofactors' for disease progression. Many potential cofactors have been investigated, including genetic factors, age, gender, route of infection, smoking, nutrition, and other infectious diseases. There is strong evidence that the disease progresses faster if HIV infection occurs at a later age.

You cannot. Worldwide, most people living with HIV have yet to develop AIDS. A fraction of people infected with HIV develop symptoms early in the course of infection, while others remain without symptoms for 15 or more years after they become infected. Because most people with HIV do not appear sick, it is impossible to tell if a person has the virus just by looking at, or talking to, him or her. People with HIV look and act just like people without HIV infection. By being tested. Detectable antibodies to HIV appear within days or weeks of initial exposure to the virus. These can be detected by a simple test that is available to you as a UN employee and to your family. Currently available tests can pick up 99.9% of infections and detect antibodies within about 3-4 weeks of infection. This 'window period' during which recent infections can be missed may be shortened by looking for portions of the virus (using antigen tests) and viral genetic material (nucleic acid-detection methods). Positive tests are normally repeated once to protect against laboratory error. Since the HIV antibody test can miss very recent infections, it is recommended that an initial negative test be followed by another antibody test within 3-6 months if possible exposure to the virus was very recent.

For detailed information about HIV and AIDS here are sites that we recommend:

• 25 years of AIDS factsheet
  This year will mark 25 years since scientists in the United States reported the first clinical evidence of a disease that would later become known as acquired immunodeficiency syndrome or AIDS. A factsheet on the history of the epidemic can now be found on the UNAIDS website.
• The HIV Life Cycle
  A comprehensive description of the HIV Life cycle, by AIDSMEDS.org
• Stages of HIV infection
  A description by AVERT.org, a UK based charity
• Questions and Answers: HIV is the Cause of AIDS
  Information by Centers for Disease Control and Prevention