AIDS (acquired immunodeficiency syndrome)

Acquired immunodeficiency syndrome (AIDS) is a disease caused by the human immunodeficiency virus (HIV). HIV damages the immune system by attacking certain white blood cells called lymphocytes (specifically those called helper T cells). Lymphocytes normally help to protect the body against invading microorganisms. When these cells are destroyed, the body loses its ability to fight infection and becomes vulnerable to a variety of infections and rare cancers that are the hallmarks of AIDS.

From 1981 (when cases of AIDS were first recorded) through 2000, more than 753,000 cases of AIDS had been reported in the United States, resulting in over 360,000 deaths, 5,086 of which were children under the age of 15. It is the leading cause of death for people between the ages of 25 and 44. The World Health Organization estimated that at the beginning of the twenty-first century, 36.1 million adults and children around the world were living with AIDS or the virus. An estimated 21.8 million people have died from AIDS since the epidemic began. In 2000 alone, AIDS caused the deaths of an estimated 3 million people, including 1.3 million women and 500,000 children under 15. Eighty percent of those deaths occurred in Africa. Cases in Eastern Europe and Russia almost doubled in 2000. No cure has yet been found for the disease, and no vaccine is presently available to prevent it.

History and spread of AIDS

In the late 1970s, a rare form of cancer called Kaposi's sarcoma and an unusual type of pneumonia called Pneumocystis carinii began to appear in previously healthy homosexual and bisexual men in the United States. It was found that the patient's immune systems were not functioning properly, causing them to be susceptible to diseases that would not normally occur in a healthy person. Named AIDS in 1981, this destruction of the immune system also began to be seen among intravenous drug users, persons who had received blood transfusions, and sexual partners of people with the disease. It was determined that AIDS was caused by a virus that could be passed from person to person through contact with blood or bodily fluids. In 1983, the virus believed to cause AIDS was discovered and named HTLV-III (human T-cell lymphotropicvirus type III). It's name was soon changed to human immunodeficiency virus, or HIV.

In early 2000, scientists at the Los Alamos National Lab in New Mexico traced the origin of the AIDS epidemic to one or a small group of humans around 1930. Previously, scientists had believed the epidemic arose around the 1950s. Experts now believe that the original virus normally infected chimpanzees. Somehow it spread to people, perhaps through a bite or a hunting mishap, in west equatorial Africa. Just when and how this happened still mystifies scientists.

How HIV damages the immune system

HIV damages the immune system by invading infection-fighting lymphocytes called helper T cells and eventually killing them. HIV enters helper T cells, then replicates (makes exact copies of itself) and produces new virus particles that are released into the bloodstream to attack other cells. A person infected with HIV may have no symptoms for 10 years or more before progressing to AIDS. In fact, by the late 1990s, some people who had been diagnosed as HIV-positive seemed to have been able to "beat" the virus before it turned into full-blown AIDS. After treatment with a combination of drugs—known informally as cocktails—the levels of HIV in their blood decreased dramatically or even disappeared. (It is still unclear how these patients will fare over the long run.) Once a person is diagnosed with full-blown AIDS, however, survival rates drop sharply; death often occurs within five years.

Methods of transmission

AIDS can be transmitted through semen or vaginal fluids during unprotected sex with an infected person and through direct contact with infected blood. Intravenous drug users who share hypodermic needles are at an especially high risk. The AIDS virus can also be passed from an infected mother to her unborn child. Since screening measures began in 1985, transmission of the disease through transfusions of donated blood or blood products is now rare.

Scientists do not believe AIDS can be transmitted through saliva. There are enzymes in saliva that can break down the virus, and the pH (measure of the acidity of a solution) of the mouth is detrimental to the survival of the virus.

Mature HIV viruses (above) and the lymphocyte from which they emerged (below). Two immature viruses can be seen budding on the surface of the lymphocyte (right of center). (Reproduced by permission of

Photo Researchers, Inc.

)

Stopping the spread of AIDS

Efforts by health officials to stop the spread of AIDS have included urging couples to use condoms when engaging in sexual intercourse and promoting sex education. In addition, certain communities have instituted needle-exchange programs, in which intravenous drug users can turn in used hypodermic needles for new sterile ones.

HIV does not survive well outside the human body. It can be easily killed or deactivated by using heat, hand soap, hydrogen peroxide, or any solution containing 25 percent alcohol, bleach, Lysol, or other disinfectants.

AIDS therapies, vaccines, and a new treatment approach

There is presently no cure for AIDS. However, new therapies involving a combination of old drugs such as AZT and new drugs called protease inhibitors (the aforementioned cocktails) have shown some success in preventing HIV from reproducing itself once infection has taken place. This has the effect of reducing the amount of the virus present in the blood and seems to postpone the onset of full-blown AIDS in patients with early HIV infection. For those who already suffer from AIDS, the new therapies may help extend the lives of some patients. Research into developing an effective vaccine to prevent AIDS is ongoing, including the testing of several experimental AIDS vaccines. A new class of drugs, called entry inhibitors, works to block HIV before it even enters the cells of an infected person. These drugs may be made available to patients as early as 2002 or 2003. At the beginning of 2001, 18 anti-retroviral agents were available for prescription, either alone or in combination.

In early February 2001, federal health officials called for a new approach to treating people infected with the AIDS virus. Since the development of protease inhibitors and so-called drug cocktails in the mid-1990s, physicians have been quick to treat people infected with the virus, even if they were otherwise healthy. This "hit early, hit hard" approach was undertaken with hopes that, in a short time, the drugs might eliminate HIV from the body of an infected person.

However, research at the beginning of the twenty-first century showed that the drug cocktails do not cure HIV; once a person stops taking the drugs, the virus rebounds. This means that the person will have to continue taking the drugs throughout his or her life. In addition, researchers found that people undergoing the drug therapy suffered a higher risk of nerve damage, weakened bones, diabetes, high levels of cholesterol, and other serious side effects.

To limit these toxic side effects, health officials urged that treatment using the drug cocktails be delayed for as long as possible for people who had HIV but did not show outward symptoms. The officials believed that in early treatment, the side effects tipped the balance between benefitting infected individuals and making their health worse.

[ See also Immune system ; Protease inhibitors ; Virus ]