STD: Bacterial

Human Immunodeficiency Virus (HIV), the agent that causes Acquired Immune Deficiency Syndrome (AIDS), is a relatively recently discovered virus. The virus was isolated in 1983 and linked to AIDS in 1984. In 1985 a serologic test was developed to identify HIV, and since then the seroprevalence of the disease in the United States and across the world has been under careful scrutiny. The attention paid to HIV disease and AIDS since its discovery has been exponential, resulting in significant information in HIV virology, its pathogenesis, and treatment. The rate at which information flows within the study of HIV is unsurpassed by any other disease. Because it is a virus that is transmitted sexually, it is mentioned here. However, the following discussion represents only the briefest of introductions into this vast field of study. Any serious student of HIV disease or AIDS need first become well acquainted with human immunology before delving into the subject.

HIV is found in every country of the world. It was estimated that by the end of 1999, over 32.4 million adults were infected with the virus, as well as 1.2 million children. In the U.S., AIDS is the leading cause of death for certain groups of 25 to 44 year- olds. Since HIV is spread through sexual contact and exposure to blood products, characteristics of the AIDS epidemic are directly related to the practice of risky behaviors, such as unprotected sex or injection drug use. In the United States, HIV infection was initially concentrated in the male homosexual population. However the proportion of people newly infected who obtained the infection through heterosexual contact continues to increase significantly; outside of the U.S., heterosexual contact is the predominant mode of transmission. Mothers also pass the virus on to their children during pregnancy, birth or breastfeeding. Until the blood supply was screened beginning in 1985, some people who became infected did so via blood transfusions or through medical treatments that contained blood products.

HIV consists of icosahedral virions with two major envelope proteins, gp120 and gp41. The virus is classified as a retrovirus, in which the enzyme reverse transcriptase is responsible for the conversion of its RNA to DNA. Once inside its host, HIV binds to the CD4 molecule, which is a protein found primarily on a subset of lymphocytes, as well as on macrophages and dendritic cells. The life cycle of HIV in the host is complicated, lengthy, and varied, and is characterized by periods of quiescence and activity. The hallmark of HIV disease is its ability to evade clearance from the immune system, instead taking up residence in lymphoid tissue and establishing a chronic, long term infection in which the host's immune system is slowly destroyed. The median length of time between initial infection and clinical illness is ten years.

Transmission of HIV occurs through direct entrance of the virus into the bloodstream via infected blood or products made with infected blood. This can occur through such risky behaviors as sharing injection needles, injuries with sharp and contaminated objects, maternal-fetal transmission through the placenta or during birth, or sexual intercourse in which there is some bleeding. Blood transfusions are also a method of transmission. Since 1985, the U.S. blood supply has been screened, and since then transfusion has been an extremely rare method of HIV transmission. However, other countries around the world may lack the resources to screen their blood supplies.

HIV transmission also occurs through mucosal linings of the body, such as vaginal, rectal, urethral, oral and gastrointestinal mucosa. Bodily fluids known to contain concentrations of HIV great enough to transmit the virus, in addition to blood, include semen, vaginal fluids and breastmilk. As a result, sexual activity and breastfeeding are major modes of transmission of the virus. When the non-infected sexual partner engages in unprotected sexual activity with an infected partner his or her chances of acquiring the virus are increased if he or she already harbors an STD, since any local infection will likely cause irritation to the urogenital mucosa.

As stated earlier, the signs and symptoms of HIV disease and AIDS are varied and extensive and will not be discussed here. Any person diagnosed with an STD, or who has engaged in unprotected sexual activity or other risky behaviors, may decide to undergo HIV testing. If a person has engaged in risky behavior with someone they know is HIV positive, they should seek medical help immediately following the risky behavior. If a person has engaged in risky behavior with one or more people in his or her past and wishes to receive an HIV test, they can undergo serologic testing. The HIV test is a test for antibodies to the virus, antibodies that can take weeks to months to develop in sufficient enough quantities to be detectable on the HIV tests that are currently available. Therefore, HIV tests reliably give information on a person's HIV status as of six months prior to the test, and not information on the person's current HIV status. This six-month time frame is called the "window period."

As is widely known, there is no cure for HIV disease or AIDS; there is only management of the symptoms. Therefore, all efforts should be made toward prevention of disease. Prevention of HIV disease includes engaging in "safer sex" (see Prevention section in the introduction), not sharing needles during injection drug use activities, and adherence to OSHA (Occupational Safety and Health Administration) guidelines when working with blood or bodily fluids.