Introduction
The term AIDS is the commonly used name for the deadly disease called acquired immunodeficiency syndrome. AIDS is caused by the human immunodeficiency virus, or HIV. The virus slowly attacks and destroys the immune system, which is the body's natural way of fighting disease and infection. When the immune system stops working, a person can pick up infections and illnesses that can eventually cause death.
HIV
A virus is a tiny particle that can reproduce only after invading a living cell of an animal, plant, or bacteria. The main target of HIV is a special type of white blood cell essential to the human immune system. These cells are known as helper T lymphocytes, or helper T cells. (Helper T cells are also called CD4+ T cells because they have on their surfaces a protein called CD4.) Helper T cells play a major role in developing the body's defensive response to disease and infection. They activate almost all the other cells in the immune system.
After entering a helper T cell, HIV multiplies very quickly. This rapid reproduction makes the virus difficult for the immune system or drugs to fight. Most infected cells die quickly (in about one day). The number of helper T cells that are destroyed is greater than the number of new cells produced by the immune system. This leads to a decline in the number of helper T cells, which damages the immune system.
Researchers initially named the virus that causes AIDS the human T-lymphotropic virus type III, or HTLV-III. After discovering in the late 1980s that several forms of the AIDS virus existed, they renamed the original virus the human immunodeficiency virus type 1, or HIV-1. Since then another form of the virus has been named HIV-2. It can cause AIDS, but it does so more slowly than HIV-1.
Spread of the virus
HIV is passed on from one person to another. It is transmitted, or spread, when a person's bloodstream is contaminated with the body fluids of an infected person. These fluids include blood, semen, and breast milk. HIV has been found in tears and saliva, but it exists there in such small amounts that the spread of the virus through these body fluids is very rare.
HIV is usually transmitted through sexual intercourse or the sharing of needles used to inject drugs into the bloodstream. A pregnant woman infected with HIV can pass on the virus to her child during pregnancy or nursing. The HIV virus cannot pass through intact bodily surfaces, such as skin, and it quickly dies outside the human body. For this reason the virus is not spread through coughing, sneezing, or routine physical contact such as shaking hands. Blood transfusions—the transfer of one person's blood to another for medical reasons—were once a major cause of HIV infection. Today, however, the risk of getting the virus from a blood transfusion is very small. In the United States, all donated blood is tested for HIV and discarded if there is evidence of infection.
Stages of infection
The course of HIV infection involves a number of stages. In the first stage HIV invades the body's cells and reproduces rapidly. Many people recently infected by HIV look and feel healthy. Other people, however, develop a flulike illness that usually lasts about one to two weeks. The symptoms include joint and muscle pain, fever, rash, sore throat, and swollen lymph glands.
After this initial stage, an infected person may go for years without any symptoms of illness. During this period, however, the virus continues to reproduce and the number of helper T cells slowly decreases. As the immune system weakens, the infected person begins to experience opportunistic infections—that is, infections that arise only in people with a damaged immune system. The body is unable to defend itself against illnesses that would not affect a healthy person. This is AIDS, the final stage of HIV infection.
The most common opportunistic infections include tuberculosis and a type of pneumonia. AIDS sufferers are also more likely to develop certain tumors, particularly a rare form of cancer called Kaposi's sarcoma. The AIDS virus may also attack the nervous system and cause brain and eye damage.
A small proportion of people infected with HIV has survived longer than ten years without developing AIDS. These people may be infected with a weakened strain of the virus, or their immune systems might fight the virus more strongly than those of other people. Even when infected people appear healthy, however, they can still pass the virus on to others.
Prevention and treatment
Despite much research, no cure or effective vaccine for HIV infection has yet been found. Efforts at preventing AIDS have focused on stopping the spread of HIV. Preventive methods include practicing safe sex by using condoms, discouraging needle sharing among drug users, and the screening of blood used for transfusions.
The treatment of AIDS was initially limited to treatment of the individual infections as they arose. Since then, however, researchers have developed a number of drugs that stop the action of enzymes that HIV needs to do its work. These drugs are most effective when several of them are used together. This is known as combination treatment. Although the drugs do not wipe out HIV altogether, they slow down or stop its reproduction. The immune system is then able to recover and fight the virus more effectively.
History
AIDS was first identified in 1981 in the United States. Most of the early AIDS cases in the United States affected homosexual men. Other early AIDS patients were drug users who got the disease by sharing contaminated needles. HIV was identified as the cause of the disease in 1983. By 1985 tests to detect the virus had been developed.
Within a decade of the first AIDS case, the disease spread all over the world. It became clear that anyone—not just homosexuals and drug users—could be at risk. People with AIDS included patients infected during blood transfusions, women infected by their male sexual partners, and children infected by their mothers before birth. Public awareness of AIDS spread as several famous people became victims of the disease, including actor Rock Hudson, basketball superstar Magic Johnson, and tennis legend Arthur Ashe.
By the end of 2002 about 42 million people worldwide were living with HIV or AIDS. More than 3 million people died from AIDS in 2002 alone. African countries south of the Sahara accounted for about 70 percent of all infections. Another area of high incidence was South and Southeast Asia, with about 14 percent of all global cases. Rates of infection were lower in other parts of the world, but the disease was spreading rapidly in eastern Europe, central Asia, China, and other places.
