AIDS stands for acquired immune deficiency syndrome, a condition in which the body's immune system breaks down. Normally, the immune system fights off infections and certain other diseases. When the system fails, a person with AIDS can develop a variety of life-threatening illnesses. An estimated 900,000 people in the United States are currently infected with HIV. There are over 38,000,000 people living with HIV in the world (reference). People who have AIDS are very susceptible to many life-threatening diseases, called opportunistic infections, and to certain forms of cancer. Transmission of the virus primarily occurs during sexual activity and by sharing needles used to inject intravenous drugs.
A virus called the human immunodeficiency virus, or HIV, causes AIDS. There are 2 forms of the virus: HIV1 and HIV2. HIV is unique among infective agents because its target is a major component of the immune system. It destroys the body’s ability to protect itself. The immune system is designed to distinguish “self” from “non-self”, or foreign. Substances recognized as foreign are usually attacked and destroyed by the immune system. Examples of foreign substances include microorganisms (germs) and some cancer cells. People with normal immunity are called immunocompetent, while individuals with impaired immunity are known as immunodeficient. Simplistically, the immune system has 2 components: blood-borne, or humoral immunity, and cell-mediated immunity. Humoral immunity is characterized by the presence and activity of immunoglobulins or antibodies. Blood-borne immunity is specialized to attack foreign substances in the blood. Cell-mediated immunity (CMI) utilizes white blood cells to destroy foreign substances such as viruses. CMI is specialized to attack foreign substances that are residing within body cells. A critical white blood cell in this process is the CD4 lymphocyte, also known as a helper lymphocyte. HIV infects and destroys helper lymphocytes, resulting in impaired CMI. It should be noted that there is considerable interplay or cross talk between humoral immunity and CMI. While deficient CMI is a hallmark of AIDS, these patients also have substandard humoral immunity.
Research has revealed a great deal of valuable medical, scientific, and public health information about HIV infection and AIDS; the ways in which HIV can be transmitted have been clearly identified. HIV is spread in the following ways:
• by sexual contact with an infected person
• by sharing needles and/or syringes (primarily for drug injection) with someone who is infected
• through transfusions of infected blood or blood clotting factors (less common and now very
rare in countries where blood is screened for HIV antibodies). The US started screening blood for HIV1 in 1985 and the less common HIV2 in 1992 (reference).
• from an HIV-infected mother to her baby before or during birth, or through breast-feeding after birth
• In the health-care setting, workers have been infected with HIV after being stuck with needles containing HIV-infected blood or, less frequently, after infected blood comes in contact with the worker's open cut or splashes into a mucous membrane (e.g., eyes or inside of the nose).
If HIV is spread through sexual contact it is important to screen for other sexually transmitted diseases.
Diagnosis
Diagnosis of HIV infection is usually done through the ELISA test, which examines a blood sample for the presence of antibodies directed against HIV (anti-HIV antibodies). If the initial test is positive, the Western Blot, a confirmatory test, will be performed. Because it can require several weeks to detect anti-HIV antibodies, a newly infected patient may test negative for the antibody. Blood samples may also be tested for the presence of HIV. The amount of virus in blood is known as the viral load. Higher viral loads correlate with more rapid disease progression. It should be noted that low concentrations of HIV in blood might not be detected.
The virus
HIV is a simple life form containing genetic information inside a protective capsule. The capsule is made of proteins and lipids. HIV does not have all of the components necessary to live. Instead, it enters some human cells and utilizes the cells’ ability to perform necessary functions. The process by which the virus gains entry into the cell is called fusion. The genetic information of HIV is composed of ribonucleic acid (RNA). During viral reproduction or replication, the genetic information must first be converted into deoxyribonucleic acid (DNA). This process is called reverse transcription. An enzyme or catalyst called reverse transcriptase facilitates the process of making DNA from RNA. The information in DNA is then used to make proteins. A critical protein in viral replication is protease. The significance of these terms will be noted in “Treatment”.
