How HIV Causes AIDS
How HIV Causes AIDS
An important focus of the National Institute of Allergy and Infectious Diseases (NIAID) is research devoted to the pathogenesis of human immunodeficiency virus (HIV) disease ¾ the complex mechanisms that result in the destruction of the immune system of an HIV-infected person. A detailed understanding of HIV and how it establishes infection and causes the acquired immunodeficiency syndrome (AIDS) is crucial to identifying and developing effective drugs and vaccines to fight HIV and AIDS. This fact sheet summarizes what scientists are learning about this process and provides a brief glossary of terms.
HIV disease is characterized by a gradual deterioration of immune function. Most notably, crucial immune cells called CD4+ T cells are disabled and killed during the typical course of infection. These cells, sometimes called "T-helper cells," play a central role in the immune response, signalling other cells in the immune system to perform their special functions.
A healthy, uninfected person usually has 800 to 1,200 CD4+ T cells per cubic millimeter (mm3) of blood. During HIV infection, the number of these cells in a person's blood progressively declines. When a person's CD4+ T cell count falls below 200/mm3, he or she becomes particularly vulnerable to the opportunistic infections and cancers that typify AIDS, the end stage of HIV disease. People with AIDS often suffer infections of the intestinal tract, lungs, brain, eyes and other organs, as well as debilitating weight loss, diarrhea, neurologic conditions and cancers such as Kaposi's sarcoma and lymphomas.
Most scientists think that HIV causes AIDS by directly killing CD4+ T cells or interfering with their normal function, and by triggering other events that weaken a person's immune function. For example, the network of signalling 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 people with AIDS.
Although HIV was first identified in 1983, studies of previously stored blood samples indicate that the virus entered the U.S. population sometime in the late 1970s. In the United States, 612,078 cases of AIDS, and 379,258 deaths among people with AIDS had been reported to the Centers for Disease Control and Prevention (CDC) as of June 30, 1997. AIDS is now the second leading killer of people aged 25 to 44 in this country. Despite an overall stabilization in the number of new AIDS cases in this country, the epidemic continues to accelerate in certain segments of the population, notably among women and injection drug users.
Worldwide, an estimated 30.6 million people were living with HIV/AIDS as of December 1997, a figure that is projected to reach 40 million by the year 2000. More than 75 percent of all adult HIV infections have resulted from heterosexual intercourse. Through 1997, cumulative HIV/AIDS-associated deaths worldwide numbered approximately 11.7 million ¾ 9 million adults and 2.7 million children.
Overview
HIV disease is characterized by a gradual deterioration of immune function. Most notably, crucial immune cells called CD4+ T cells are disabled and killed during the typical course of infection. These cells, sometimes called "T-helper cells," play a central role in the immune response, signalling other cells in the immune system to perform their special functions.
A healthy, uninfected person usually has 800 to 1,200 CD4+ T cells per cubic millimeter (mm3) of blood. During HIV infection, the number of these cells in a person's blood progressively declines. When a person's CD4+ T cell count falls below 200/mm3, he or she becomes particularly vulnerable to the opportunistic infections and cancers that typify AIDS, the end stage of HIV disease. People with AIDS often suffer infections of the intestinal tract, lungs, brain, eyes and other organs, as well as debilitating weight loss, diarrhea, neurologic conditions and cancers such as Kaposi's sarcoma and lymphomas.
Most scientists think that HIV causes AIDS by directly killing CD4+ T cells or interfering with their normal function, and by triggering other events that weaken a person's immune function. For example, the network of signalling 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 people with AIDS.
Scope of the HIV Epidemic
Although HIV was first identified in 1983, studies of previously stored blood samples indicate that the virus entered the U.S. population sometime in the late 1970s. In the United States, 612,078 cases of AIDS, and 379,258 deaths among people with AIDS had been reported to the Centers for Disease Control and Prevention (CDC) as of June 30, 1997. AIDS is now the second leading killer of people aged 25 to 44 in this country. Despite an overall stabilization in the number of new AIDS cases in this country, the epidemic continues to accelerate in certain segments of the population, notably among women and injection drug users.
Worldwide, an estimated 30.6 million people were living with HIV/AIDS as of December 1997, a figure that is projected to reach 40 million by the year 2000. More than 75 percent of all adult HIV infections have resulted from heterosexual intercourse. Through 1997, cumulative HIV/AIDS-associated deaths worldwide numbered approximately 11.7 million ¾ 9 million adults and 2.7 million children.
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