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13.56: HIV and AIDS

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    How long can a person live with HIV?

    Years ago, a diagnosis of an HIV infection was a death sentence. Not today. With the proper medical treatment, an individual can live well over 10 or 20 or more productive years with an AIDS diagnosis. One of the most famous individuals with HIV is Earvin “Magic” Johnson, a retired professional basketball player. He was diagnosed in 1991. Over 20 years later, he is still doing well.

    HIV and AIDS

    Human immunodeficiency virus (HIV) is a virus that attacks the immune system. An example of HIV is shown in Figure below. Many people infected with HIV eventually develop acquired immune deficiency syndrome (AIDS). This may not occur until many years after the virus first enters the body.

    HIV virus

    HIV is a virus that attacks cells of the immune system.

    HIV Transmission

    HIV is transmitted, or spread, through direct contact of mucous membranes or body fluids such as blood, semen, or breast milk. As shown in Figure below, transmission of the virus can occur through sexual contact or the use of contaminated hypodermic needles. It can also be transmitted through an infected mother’s blood to her baby during late pregnancy or birth or through breast milk after birth. In the past, HIV was also transmitted through blood transfusions. Because donated blood is now screened for HIV, the virus is no longer transmitted this way. HIV is not spread through saliva, touching or in swimming pools.

    HIV modes of transmission

    HIV may be transmitted in all of the ways shown here. Based on how HIV is transmitted, what can people do to protect themselves from becoming infected? What choices can they make to prevent infection?

    HIV and the Immune System

    HIV infects and destroys helper T cells. As shown in Figure below, the virus injects its own DNA into a helper T cell and uses the T cell’s “machinery” to make copies of itself. In the process the T cell is destroyed, and the virus copies go on to infect other helper T cells.

    HIV mechanism for destroying T cells

    This diagram shows how HIV infects and destroys T cells.

    HIV is able to evade the immune system and keep destroying T cells. This occurs in two ways:

    • The virus frequently mutates and changes its surface antigens. This prevents antigen-specific lymphocytes from developing that could destroy cells infected with the virus.
    • The virus uses the plasma membranes of host cells to hide its own antigens. This prevents the host’s immune system from detecting the antigens and destroying infected cells.

    As time passes, the number of HIV copies keeps increasing, while the number of helper T cells keeps decreasing. The graph in Figure below shows how the number of T cells typically declines over a period of many years following the initial HIV infection. As the number of T cells decreases, so does the ability of the immune system to defend the body. As a result, an HIV-infected person develops frequent infections. Medicines can slow down the virus but not get rid of it, so there is no cure at present for HIV infections or AIDS. There also is no vaccine to immunize people against HIV infection, but scientists are working to develop one.

    CD4 T cell count during HIV infection

    It typically takes several years after infection with HIV for the drop in T cells to cripple the immune system. What do you think explains the brief spike in T cells that occurs early in the HIV infection shown here?


    AIDS is not a single disease but a set of diseases. It results from years of damage to the immune system by HIV. It occurs when helper T cells fall to a very low level and opportunistic diseases occur (see Figure above). Opportunistic diseases are infections and tumors that are rare except in people with immunodeficiency. The diseases take advantage of the opportunity presented by people whose immune systems can’t fight back. Opportunistic diseases are usually the direct cause of death of people with AIDS.

    AIDS and HIV were first identified in 1981. Scientists think that the virus originally infected monkeys but then jumped to human populations, probably sometime during the early to mid-1900s. This most likely occurred in West Africa, but the virus soon spread around the world (see Figure below). Since then, HIV has killed more than 25 million people worldwide. The hardest hit countries are in Africa, where medicines to slow down the virus are least available. The worldwide economic toll of HIV and AIDS has also been enormous.

    HIV global rates of infection

    This map shows the number of people in different countries with HIV infections and AIDS in 2008. The rate of spread of the infection is higher Africa than in the U.S., yet the U.S. has a relatively large number of people with HIV infections and AIDS. Why might there be more survivors with HIV infections and AIDS in the U.S. than in Africa?

    HIV Research: Beyond the Vaccine

    Over the past 15 years, the number of people who die of AIDS each year in the United States has dropped by 70 percent. But AIDS remains a serious public health crisis among low-income African-Americans, particularly women. And in sub-Saharan Africa, the virus killed more than 1.6 million people in 2007 alone. Innovative research approaches could lead to new treatments and possibly a cure for AIDS. HIV/AIDS has been described as a disease of poverty. Individuals with poor access to health care are less likely to see a doctor early on in their HIV infection, and thus they may be more likely to transmit the infection. HIV is now the leading cause of death for African American women between 24 and 35 years old.

    For patients who have access to drugs, infection with the virus has ceased to be a death sentence. In 1995, combinations of drugs called highly active anti-retroviral therapy (HAART) were developed. For some patients, drugs can reduce the amount of virus to undetectable levels. But some amount of virus always hides in the body's immune cells and attacks again if the patient stops taking his or her medication. Researchers are working on developing a drug to wipe out this hidden virus, which could mean the end of AIDS.


    • HIV is a virus that attacks cells of the immune system and eventually causes AIDS.
    • AIDS is the chief cause of immunodeficiency in the world today.


    1. What is the relationship between HIV and AIDS?
    2. Identify two ways that HIV can be transmitted.
    3. What cells are affected by HIV?
    4. What happens to the number of HIV copies and the helper T cells over time in an infected individual?
    5. Draw a graph to show the progression of an untreated HIV infection. Include a line that shows how the number of HIV copies changes over time. Include another line that shows how the number of helper T cells changes over time.
    6. What are opportunistic diseases?

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