AIDS

AIDS is the abbreviation for acquired immunodeficiency syndrome. The syndrome is caused by several types of a virus that is now known as the human immunodeficiency virus (HIV). AIDS is characterized by the destruction of cells that are vital to the proper operation of the immune system. People afflicted with AIDS can develop opportunistic infections; life-threatening illnesses caused by viruses or bacteria that do not sicken those with healthy immune systems. Certain types of cancers can also develop in people with AIDS.

AIDS was first detected in the 1981. At that time, the malady was not named. The identification as AIDS came in 1982. The designation of the illness as a syndrome reflected the observations that a variety of clinical symptoms were apparent, rather than a single disease.

Mature HIV-1 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). Photograph by Scott Camazinr. National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.

Since the early 1980s, the number of cases has increased tremendously. As of 2002, more than 790,000 Americans are known to have AIDS. Globally, approximately 40 million people have AIDS, almost three million of these being children, with five million new cases being reported in 2001. The disease is considered to be an epidemic, especially in the world's population of black men ages 25-44, where AIDS is the leading cause of death. In 2001, three million people died of AIDS related complications and opportunistic infections.

The viral cause of AIDS was first reported in 1983 by researchers at the Pasteur Institute in France. Then, the virus was named lymphadenopathy-associated virus or LAV. The next year, researchers in the United States reported their discovery of a virus that they designated human T cell lymphotropic virus, type 3 (HTLV-III). After some controversy, it was later shown that the two viruses were the same.

The name of the virus was later changed to HIV, and later still to HIV-1. The origin of the virus remains unclear. The earliest known case is from blood sample collected in 1959 from a man in Kinshasa, Democratic Republic of Congo. A speculation, still unresolved, is that prior to this time the virus was resident in primates. Indeed, an AIDS-like virus (simian immunodeficiency virus or SIV) is present in primates.

HIV-2 was discovered in 1984. The virus is similar to, but distinct from, HIV-1. AIDS caused by HIV-2 is slower to develop and the symptoms are milder than those caused by HIV-1. The designation HIV typically refers to both viral types.

Both HIV-1 and HIV-2 can be transferred from person to person during sexual contact, via infected semen. Initially, AIDS was thought to be exclusively a disease of gay males and certain racial groups. This led to a backlash against these groups. But, with time, it became clear that AIDS could infect anyone.

Maternal transfer of HIV to a developing fetus can occur, as can transmission to a nursing baby via infected breast milk. Transmission via infected blood also occurs, during a blood transfusion and the sharing of needles during the injection of illicit drugs. The possibility of blood born transmission in transfusions is far less now than in the 1970s and 1980s, because blood is now rigorously screened for the presence of the virus and is also heat treated to render the virus incapable of replicating.

AIDS is a progressively worsening disease. It can be difficult to diagnose during the early stages of infection, since symptoms that appear are similar to those of influenza. These symptoms include fever, headache, fatigue, and enlarged lymph nodes. Often these symptoms disappear within a week to a month.

A period follows where no symptoms are apparent. This "asymptomatic" period can be anywhere from several months to ten or more years. Although no symptoms are apparent, the virus is multiplying in cells of the immune system. This replication destroys the immune cells, in particular a class of cells called CD4 positive T cells (T4 cells). Indeed, the decline in T4 cells can alert a physician to the possibility of AIDS. An infection can also be detected by the presence of antibodies to the virus in the blood. However, such a test is usually done only when symptoms appear, unless a person suspects that they have been exposed to the virus.

T4 cells are one of the immune system's vital defenses against infection. So, their destruction produces a variety of symptoms. These symptoms include a loss of energy, loss of weight, the frequent development of fevers, frequent yeast infections in the mouth (thrush) or vagina, chronic skin rashes, and infections caused by the herpes virus. In infected children, growth can be slowed down.

Individuals are diagnosed with AIDS when the T cell count in their blood declines to 200 or less (healthy people have a T cell count of 1,000 or more), and when certain hallmark symptoms develop.

People with AIDS are prone to developing certain cancers. These include cancers caused by certain viruses (Kaposi's sarcoma and cancer of the cervix), and cancers of the immune system (lymphomas).

Treatment for AIDS is varied. Some treatments are geared toward the early stages of HIV infection, while other treatments are targeted at events that occur later in HIV infection. Still other treatments are intended to combat the opportunist microbes that cause infections.

The early stages of HIV infection involve the making of new copies of the virus. HIV is a retrovirus, and so contains ribonucleic acid (RNA) as the genetic material. Since the host cell that the virus infects contains deoxyribonucleic acid (DNA) as the genetic material, HIV must produce DNA. This is accomplished using a viral enzyme called reverse transcriptase. Drugs that inhibit the action of reverse transcriptase can prevent HIV from making new copies of itself. Some examples of reverse transcriptase inhibitors include azidothymidine (AZT; Retrovir^®), stavudine, and lamivudine.

Other drugs known as protease inhibitors block the action of a protein that is vital for viral replication. Protease inhibitors act at a later step in the virus manufacture process. Examples of protease inhibitors are ritonavir, amprenavir, and lopinavir.

Often the drugs are given in combination, to overcome the development of virus resistance to any one drug. The use of reverse transcriptase inhibitors along with protease inhibitors is called highly active antiretroviral therapy, or HAART. HAART has shown positive results in people recently infected with HIV and those who have developed AIDS. Unfortunately, HAART can produce side effects, including death. As well, an intolerance to the drugs can develop, necessitating a change in the types of drugs being taken.

Treatment can also be directed at microbes that cause the opportunistic infections, rather than the HIV. Specific drugs are used to treat viral infections of the eye, and infections caused by yeast and fungi.

One of the most common and deadly opportunistic infections is that caused by the fungus Pneumocystis carinii. The fungus is common in the body. The lung infection caused by the fungus (Pneumocystic carinii pneumonia, or PCP) does not usually occur in a person with a healthy immune system.

As of 2002, there is no vaccine for AIDS. Indeed, some AIDS researchers are not optimistic that an effective vaccine will soon be developed, given that the virus replicates inside host cells where it is shielded and the often extended period between initial infection and the appearance of symptoms. The use of creams that contain HIV-inactivating chemicals, which would be applied prior to sex, is being explored. Currently, the avoidance of high risk activities, such as unprotected sex with someone whose sexual history is unknown, is the best means of minimizing the chance of developing AIDS.