HIV Infection and AIDS Health Article

Definition

Human immunodeficiency virus (HIV) is a retrovirus that causes acquired immune deficiency syndrome (AIDS) by infecting helper T cells of the immune system. The most common serotype, HIV-1, is distributed worldwide, while HIV-2 is primarily confined to West Africa. AIDS is a severe immunological disorder caused by the retrovirus HIV, resulting in a defect in cell-mediated immune response that is manifested by increased susceptibility to opportunistic infections and to certain rare cancers, especially Kaposi's sarcoma. It is transmitted primarily by exposure to contaminated body fluids, especially blood and semen. Everybody who has AIDS also has HIV disease, but not everybody with HIV disease is classified by the United States (U.S.) government as having AIDS. The U.S. government uses CD4 cell counts (part of the immune system) to make this distinction.

Description

The earliest known case of HIV-1 came from a human blood sample collected in 1959 from a man in Kinshasa, Democratic Republic of Congo. The method by which he became infected is not known; however, genetic analysis of his blood sample suggested that HIV-1 might have stemmed from a single virus in the late 1940s or early 1950s. HIV has existed in the United States since the mid to late 1970s. During 1979 to 1981, rare types of pneumonia, cancer, and other illnesses were reported by physicians in Los Angeles and New York among a number of male patients who had sex with other men. Since it is rare to find these diseases in people with a healthy immune system, public health representatives became concerned that a new virus was emerging.

In 1982, the term AIDS was introduced to describe the occurrences of opportunistic infections, Kaposi sarcoma, and Pneumocystis carinii pneumonia in previously healthy persons and formal tracking of these cases in the United States began that year. The virus that causes AIDS was discovered in 1983 and named human T-cell lymphotropic virus-type III/lymphadenopathyassociated virus (HTLV-III/LAV) by an international scientific committee who later changed it to HIV. Many theories as to the origins of HIV and how it appeared in the human population have been suggested. The majority of scientists believed that HIV originated in other primates and was somehow transmitted to man. In 1999, an international group reported the discovery of the origins of HIV-1, the predominant strain of HIV in the developed world. A subspecies of chimpanzees native to west equatorial Africa were identified as the original source of the virus. The researchers believe that HIV-1 was introduced into the human population when hunters became exposed to infected blood.

Most scientists believe that HIV causes AIDS by directly inducing the death of CD4+ T cells (helper T cells in the immune system) or interfering with their normal function and by triggering other events that weaken a person's immune function. For example, the network of signaling molecules that normally regulates a person's immune response is disrupted during HIV disease, impairing a person's ability to fight other infections. The HIV-mediated destruction of the lymph nodes and related immunologic organs also plays a major role in causing the immunosuppression seen in persons with AIDS.

In the absence of antiretroviral therapy, the median time from HIV infection to the development of AIDS-related symptoms has been approximately 10 to 12 years. A wide variation in disease progression, however, has been noted. Approximately 10 percent of HIV-infected persons have progressed to AIDS within the first two to three years after infection, whereas up to 5 percent of persons have stable CD4+ T cell counts and no symptoms even after 12 or more years. Factors such as age or genetic differences among persons with HIV, the level of virulence of an individual strain of virus, and co-infection with other microbes may influence the rate and severity of disease progression. Drugs that fight the infections associated with AIDS have improved and prolonged the lives of HIV-infected persons by preventing or treating conditions such as Journal of Infectious Diseases. This approach is known formally as short-cycle structured intermittent antiretroviral therapy (SIT) or colloquially as the "7-7" approach. Dr. Mark Dybul, of the National Institute of Allergy and Infectious Diseases (NIAID) and the study author, noted that this approach together with high patient adherence could be a powerful and cost-effective tool in HIV treatment. This regimen uses half as much antiretroviral medication so not only are drug costs reduced but drug-related toxicities may be less in the long run. He believes that this is particularly important to countries with few resources around the world.