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The virus responsible for AIDS was identified in 1983 and named Human Immunodeficiency Virus, or HIV. HIV primarily infects those cells of the immune system known as helper T cells, but it also may infect brain or nerve cells. Helper T cells brain cells and nerve cells all have a particular cell surface molecule called CD4 that serves as the site of attachment for the virus. Inside the host cell the viral RNA is copied into DNA which may be integrated into the host cell genome. Each infected cell than can serve as a factory for the production of HIV. When the cell eventually ruptures hundreds of viruses each able to infect another cell, are released. Reproduction of HIV in helper T cells leads to a gradual decline in the number of helper T cells, weakened function of the immune system and increased susceptibility to opportunistic infections and cancer. Opportunistic infections are infections a normal, fully functioning immune system would be able to repel. Although HIV can damage organs directly it is the opportunistic infections that account for up to 90% of deaths from AIDS.
The incubation period for HIV infection is two weeks to three months. If an infection has occurred, HIV antibiotics can be detected in the blood at that time. The incubation period for AIDS is much longer. An individual infected with HIV may not develop AIDS for several months or even as long as 12 years. The variation in the AIDS incubation time is related to the length of time the virus remains inactive in the cells of the immune system. Symptoms vary widely depending on the type and number of opportunistic diseases that occur and often alternate with period of relatively good health.
AIDS the most severe stage of HIV infection usually leads to death within two years of diagnosis. Diagnosis is based on the presence of certain infections or cancers in a person who tests positive for HIV antibodies. Among those conditions are a variety of infections caused by fungi, protozoans, eubacteria and other viruses seldom seen in the population and type of skin cancer known as Kaposi’s sarcoma. Besides Kaposi’s sarcoma the most common opportunistic infection associated with AIDS is a pneumonia caused by a protozoan parasite Pneumocystis carinii. Tuberculosis which is caused by a eubacterium, also is prevalent among HIV infected individuals.
HIV usually is introduced into the body through sexual contact, although infection also can occur through contaminated blood. AIDS can occur in both homosexuals and heterosexuals, and heterosexual transmission is becoming more common. Abstaining from sexual activity to one no infected individual and using condoms are two other methods that reduce the risk of acquiring AIDS from sexual contact.
Many individuals with AIDS are drug addicts who use intravenous injections and have shared hypodermic needles with infected people. Some AIDS patients are hemophiliacs and other recipients of blood transfusions that contained HIV. Since 1985 however all donated blood in the United States has been tested for HIV. Because the virus can cross the placenta and infection can occur at birth or through the mother’s milk, an increasing number of AIDS cases are appearing in babies born to HIV infected mothers. Although there is no evidence that AIDS can be transmitted through casual contact such as shaking hands or swimming in the same pool, several health care workers exposed to HIV by way of accidental cuts or injections have contracted AIDS.
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