What is AIDS?

AIDS is the acronym for Acquired Immune Deficiency Syndrome. As its name implies, AIDS is acquired (rather than inherited or genetic), refers to the loss of the body's immune system, and is a syndrome--a combination of signs and symptoms that together define a pathological condition. AIDS is not actually a disease. A disease must have a single identifiable cause; for example, syphilis is caused by a specific bactera, and measles is caused by a specific virus. People with AIDS may have a number of diseases. When taken together, the diseases that manifest themselves are referred to as a syndrome.
How HIV Affects the Body

Most scientists agree that AIDS is results from infection by the human immunodeficiency virus, which causes a breakdown of the body's immune system. As the immune system breaks down, people become susceptible to a variety of illnesses known as opportunistic infections-so called because they do not occur in most healthy people, but find an "opportunity" to grow in people with compromised immune systems.

After entering the body, HIV begins to destroy several types of white blood cells. Of most concern are the CD4 cells (also known as helper T-cells or T4 cells), which help to induce an immune response. As these cells are killed, immune functioning is lost, and the body can no longer adequately protect itself against disease. The fewer T-cells that remain intact, the greater the chance that a person will succumb to various opportunistic infections and cancers. For most people with AIDS, these infections and cancers prove fatal.

After a person becomes infected with HIV, his or her immune system responds by producing antibodies to the virus. Several tests can determine whether or not a person has been infected by looking for the presence of these antibodies in the blood serum. When a laboratory test reveals antibodies to HIV in a person's blood, he or she is said to be HIV positive. The change from being HIV negative to HIV positive is called seroconversion.

The time between exposure to the virus and the appearance of antibodies is known as "the window period." During this period a person can test negative for antibodies, yet actually be infected with the virus. In most people, enough HIV antibodies to be detected by the test will appear between several weeks and three months after infection; for a small number of people, however, this time may be extended to six months. In addition, recent research suggests that those with HIV may be much. more infectious during the window period than they are during the asymptomatic phase that follows.

AIDS is a diagnostic category developed by the Centers for Disease Control and Prevention (CDC) to distinguish HIV-infected people with certain life-threatening illnesses from others infected by the virus. HIV disease includes a number of different stages. Some people are infected with the virus yet show no signs of illness. Others develop illnesses that are not life-threatening; these may come and go or persist over time. Still others develop one or more serious illnesses that lead to a diagnosis of AIDS. Thus AIDS is the clinical end stage of HIV disease.

Some people progress from infection with HIV to AIDS relatively quickly, whereas others remain healthy for a long time. Because HIV is a relatively new disease, its average or maximum latency period remains unknown. Currently, 50 % of those infected with HIV will develop AIDS within 10 years. Although it is impossible to determine whether everyone who is infected with the virus will eventually develop AIDS, researchers and health care professionals estimate the likelihood at between 95% and 99%.

Roughly 88% of the deaths associated with HIV infection and AIDS are due to opportunistic infections, 7% are due to cancer, and 5% are from other causes. The two most common diseases associated with HIV in the U.S. are Pneumocystis carinii pneumonia (PCP) and Kaposi's sarcoma (KS), a cancer of the lining of blood vessels. Although Kaposi's sarcoma can be fatal, it tends to progress relatively slowly, and most people with KS usually develop other fatal diseases. A variety of parasites, fungi, bacteria, and viruses can cause. additional diseases in numerous body systems of HIV-infected people. Organisms affecting the central nervous system, for example, cause problems ranging from minor memory loss to dementia, and those affecting the gastrointestinal system cause persistent diarrhea and wasting.

There is currently no vaccine to prevent the spread of HIV. Although historically vaccines have been the best weapons against viral diseases, developing a vaccine to fight HIV is proving particularly difficult because HIV is unlike most other viruses (Palfreman, 1994). Vaccines usually work by preventing the spread of a virus after a person has been infected. Once the virus has entered the body, the vaccine initiates an immune response that

There is currently no vaccine to prepare the spread of HIV. Although historically vaccine have been the best weapons against viral diseases, developing a vaccine to fight HIV is unlike most other viruses. Vaccines usually work by preventing the spread of a virus after a person had been infected. Once the virus has entered the body, the vaccine initiates an immune response that stops the virus at an early stage. This process cannot be used with HIV, which quickly enters cells and inserts itself into the genome. Once this is done the virus cannot be found by the immune system, so it cannot be eliminated. Additionally, unlike most other viruses, HIV mutates rapidly, thereby producing many new strains of the virus. There are currently thousands of different HIV strains, of which many can be present in an individual at the same time. To be effective, a vaccine would need the ability to protect against all these strains.

There is also no cure for the virus. Because AIDS is a syndrome with many dimensions, probably no single drug will 'provide complete treatment or cure. Numerous treatments are currently being used to slow the course of the virus and to treat or prevent the numerous opportunistic infections and cancers associated with it. People with AIDS are living longer because of improvements in treatment and prevention. Note, however, that life expectancy for people with HIV is strongly influenced by access to medical care and the available treatments.

Much of the current research in this area centers around finding drugs that will control or inactivate the virus without harming the infected person. The antiviral drug azidothymidine (AZT) was first used with AIDS patients in 1986, and is standard care for most HIV-infected adults and some children. AZT slows the destruction of the immune system that leads to AIDS, and works to reduce the frequency of opportunistic infections. Unfortunately, the positive effects of AZT diminish over time, and it has many side effects, including nausea, insomnia, vomiting, fatigue, and headaches. Development and testing of other antiviral drugs such as dideoxyinosine (ddI) and dideoxycytidine (ddC) are in progress as well.

In an attempt to find an alternative to the antiviral drugs discussed above, many scientists are now turning their attention to a class of drugs known as protease inhibitors. These drugs attempt to stop the virus from replicating itself by inhibiting the action of protease, a necessary part of the viral replication process. If successful, protease inhibitors would prevent HIV from spreading within the body. Although not a cure, this class of drugs has the potential to considerably extend a person's life span. On the negative side, protease inhibitors would have to be taken several times a day for life, and will probably be quite expensive--a severe drawback for many people in developed countries and the vast majority in developing nations.

In addition to drugs aimed at inactivating HIV, numerous drugs are available to treat or prevent opportunistic infections. For example, the use of aerosol pentamidine for both prevention and treatment of PCP has dramatically reduced the number of deaths from this type of pneumonia. Most opportunistic infections initially respond to drug treatment, but as the patient contracts multiple infections and cancers, the treatments tend to be less effective and to produce toxic reactions from drug interactions. In addition to drugs approved by the Food and Drug Administration, many alternative drugs and other types of therapies are being used by people in various stages of HIV disease.

In 1985, a second type of virus was found that causes AIDS. This virus, named HIV-2, was initially isolated in female prostitutes in West Africa. It is a genetically similar, yet distinct strain of HIV. The first confirmed case of HIV-2 infection in the U.S. was reported in 1987. Since that time, 59 cases have been reported around the country (Centers for Disease Control, 1995). Clinically, HIV-1 (as it is now called to distinguish it from HIV-2) and HIV-2 cause similar problems for those they infect, but HIV-2 appears to be less destructive to immune system cells and reproduces more slowly. Currently, HIV-2 is common in West Africa, and spreading slowly elsewhere. Because little is known about HIV-2, and the vast majority of infection in the U.S. is from HIV-1, further references to HIV in this text apply to HIV-1.

Last updated Jan 4/07