What Causes AIDS and What is HIV?

(Acquired immune deficiency syndrome) AIDS, first described in 1981, is not a single disease, but rather, an increasing vulnerability to many disorders, especially infections. These result from the progressive destruction of the immune system by the human immunodeficiency virus (HIV).

The virus is transmitted when a body fluid of an infected individual -- blood, semen, vaginal secretions, or breast milk -- is absorbed into the bloodstream of a healthy person. The major exception appears to be saliva, which has never been shown to be a carrier.

Worldwide, heterosexual intercourse is the most common mode of HIV transmission. In the United States, most cases result from male homosexual intercourse or the sharing of hypodermic needles. However, heterosexual intercourse is gaining as a source of infection, and about one-third of babies born to HIV-infected women develop AIDS. Before development of an HIV screening test in 1986, the infection was often spread through contaminated blood transfusions and the coagulation factors used to treat hemophilia.

Whenever a virus enters the body, a healthy immune system produces a variety of fighter cells, which include the T-cell lymphocytes. HIV invades T-cells and uses their genetic material to multiply itself. The virus eventually destroys the T-cells, producing many new HIV particles in the process. In time, the immune system is overwhelmed by the infection, and the person becomes increasingly susceptible to the infections and other diseases that make up the AIDS complex.

It takes an average of 10 years from the time of infection to develop fullblown AIDS, and throughout that entire period, contact with body fluids from the person harboring the virus can spread the infection.

Diagnostic Studies and Procedures

There is no direct test to diagnose an HIV infection; the tests currently available detect instead antibodies made in response to the virus. These antibodies are not detectable until at least six weeks after infection; in rare cases, it may take a year or more for them to develop. A negative result, therefore, does not necessarily rule out the existence of an HIV infection.

The most common test for HIV is a blood analysis called ELISA, short for enzyme-linked immunosorbent assay. Because the ELISA test can be falsely positive, however, a firm diagnosis also requires a positive response to another antibody test called the Western blot test, which specifically detects HIV antibodies. Once an HIV infection has been confirmed, frequent blood tests to measure T-cell levels will indicate just how fast the disease is progressing, even in the absence of any symptoms.

Medical Treatments

AIDS remains incurable so far, but there are several drugs that delay the onset of AIDS symptoms, and other drugs and vaccines are in the testing stage. While none of the medications below appear to prolong life, any of them may extend the period of relative health, especially when used early in the infection.

Azidomymidine (AZT). The first AIDS drug, this gained FDA approval in 1987. It works by interfering with replication of the HIV within the T-cells. Contrary to early optimistic expectations, it does not prolong life, but it does delay the onset of AIDS symptoms. Doctors disagree, however, on whether AZT should be initiated as soon as a patient tests HIV positive and risk its side effects (which include anemia and reduced white blood cells), or whether they should wait for symptoms.

Dideoxyinosine (DDI). This drug is similar to AZT, but it has different adverse effects, such as pancreatitis and nerve problems. Thus, DDI may be taken by patients who are unable to tolerate AZT.

Dideoxycytidine (DDC). Used in combination with AZT, this drug helps to prevent the virus from multiplying.

Erythropoietin. This synthetic hormone stimulates bone marrow cells to produce red blood cells and counter anemia caused by AZT.

Interleukin-2. Infusions of this protein appear to increase T-cell production in HIV-positive individuals who do not yet have AIDS. Its use, although promising, is still experimental.

Pentamidine. This is an aerosol drug that is inhaled periodically to prevent Pneumocystis carina pneumonia, a common infection among AIDS patients.

Trimethoprim and sulfamethoxazole. Marketed as Bactrim or Septra, these antibiotics are taken either to prevent or treat Pneumocystis pneumonia.

gp-160. This is an experimental vaccine that may slow the progress of HIV, but like other vaccines that are currently being tested, it does not prevent it.

HIV infection follows an unpredictable course; no two cases are exactly the same. Additional treatments depend upon the AIDS-related diseases or infections involved. For example, AIDS increases the risk of developing cancer, notably lymphoma, Kaposi's sarcoma, and cervical cancer. These are treated by surgery, radiation, and chemotherapy. Pneumocystis pneumonia is treated with drugs, as is toxoplasmosis, a parasitic infection. Toxoplasmosis cysts may be removed surgically.

The knowledge that one is infected with HIV is also psychologically difficult to deal with. In addition to medical treatment, most doctors also advise that patients seek counseling.