Aids Disease HIV
Intro
AIDS, Acquired Immune Deficiency Syndrome is a specific group of diseases or conditions that result from the deterioration of the immune system as a result of the human immunodeficiency virus (HIV). A person infected with HIV gradually loses immune function along with certain immune cells called CD4 T-lymphocytes or CD4 T-cells, causing the infected person to become vulnerable to infection. With the loss of immune function, a group of various illnesses develops over time and eventually results in death.
History
In the early eighties, healthy homosexual men in San Francisco and New York began to become ill and develop medicine- resistant cancers. Then, drug users and hemophiliacs throughout the country began to develop the same symptoms. This began to spread to children and non-drug using women. In 1982, the term AIDS was given to the disease and HIV was determined as the cause in 1983.
In 1999, a team of scientists identified a virus called simian immunodeficiency virus (SIV) in the tissues of wild chimpanzees in west- central Africa. Researchers believe that HIV came from SIV, and that it was transmitted to humans in Africa approximately 100 years ago. We will probably never know exactly how SIV spread from chimpanzees to humans or who the first victim of HIV was. However, the consensus seems to be that it could have occurred through cuts acquired when hunters killed chimpanzees and monkeys for food. The virus that infected the hunters evolved into HIV. At first, the new disease spread slowly in sub- Saharan Africa. Then, changes such as civil wars and industrial development encouraged migration from rural areas into the cities. The disease then began to worldwide.
HIV
HIV is the cause of AIDS. Researchers have known since 1984 that HIV enters human cells by binding with a receptor protein known as CD4, located on human immune-cell surfaces. HIV carries on its surface a viral protein known as gp120, which specifically recognizes and binds to the CD4 protein molecules on the outer surface of human immune cells. HIV must also bind to chemokine receptors, small proteins also found on the surface of human immune cells, to enter the cells. The first chemokine receptor linked to HIV entry was CXCR4 (originally called fusin), which is bound by HIV strains that dominate during the latter stages of the disease. Researchers then determined that another chemokine receptor, CCR5, bound HIV strains that dominate in the early stages of the disease. Researchers are continuously discovering more chemokine receptors.
Any human cell that has the correct binding molecules on its surface is a potential target for HIV infection. However, it is the specific class of human white blood cells called CD4 T-cells that are most affected by HIV because these cells have numerous CD4 molecules on their outer surfaces. HIV replication in CD4 T-cells can kill the cells directly; however, the cells also may be killed or rendered dysfunctional by indirect means without ever having been infected with HIV. CD4 T-cells are critical in the normal immune system because they help other types of immune cells respond to invading organisms. As CD4 T-cells are specifically killed during HIV infection, no help is available for immune responses. General immune system failure results, permitting the opportunistic infections and cancers that characterize clinical AIDS.
Although it is generally agreed that HIV is the virus that causes AIDS and that HIV replication can directly kill CD4 T-cells, the large variation among individuals in the amount of time between infection with HIV and a diagnosis of AIDS has led to speculation that other cofactors-that is, factors acting along with HIV-may influence the course of disease. The exact nature of these cofactors is uncertain-it is believed that they may include genetic, immunologic, and environmental factors or other diseases. However, it is clear that HIV must be present for the development of AIDS.
For years scientists have speculated that HIV spread from chimpanzees to humans, but no conclusive evidence for this pattern of infection existed. Moreover, scientists did not know when the virus first infected humans; HIV could have been passed to humans centuries ago, or decades ago. Two discoveries provide clues that may help solve these mysteries. In 1998 a team of researchers identified what is believed to be the oldest known case of AIDS, an African man who died in 1959. Scientists believe that the form of HIV that killed this man, which probably first infected him in the 1940s or early 1950s, is the close ancestor of the HIV strains infecting more than 33.4 million people today. Then, in early 1999, a team of researchers found the first conclusive evidence that HIV spread from chimpanzees to humans on at least three separate occasions in central Africa, probably beginning in the 1940s or 1950s.
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