HIV/AIDS: Causes

Normally, white blood cells and antibodies attack and destroy foreign organisms that enter your body. This response is coordinated by white blood cells known as CD4 lymphocytes. Unfortunately, these lymphocytes are also the main targets of HIV, which attaches to the cells and then enters them. Once inside, the virus inserts its own genetic material into the CD4 lymphocytes and uses the material to make copies of itself.

When the new copies of the virus break out of the host cells and enter your bloodstream, they search for other cells to attack. In the meantime, the old host cells die. The cycle repeats itself again and again. In the process, more than 10 billion new HIV particles are produced every day. To counter this huge virus production, your immune system turns out as many as 2 billion new CD4 cells daily.

Eventually, however, the virus wins this race. The number of CD4 cells in your body progressively decreases, and you develop severe immune deficiency, which means your body can't effectively fight off viruses and bacteria that cause disease.

How HIV is Transmitted

 You can become infected with HIV in several ways, including:

• Sexual transmission. You may become infected if you have vaginal, anal or oral sex with an infected partner whose blood, semen or vaginal secretions enter your body. You can also become infected from shared sexual devices if they're not washed or covered with a condom. The virus is present in the semen or vaginal secretions of someone who's infected and enters your body through small tears that can develop in your rectum or vagina during sexual activity. If you already have another sexually transmitted disease, you're at much greater risk of contracting HIV. Contrary to what researchers once believed, women who use the spermicide nonoxynol-9 also may be at increased risk. This spermicide irritates the lining of the vagina and may cause tears that allow the virus into your body.
• Transmission through infected blood. In some cases the virus may be transmitted through blood and blood products — including whole blood, packed red cells, fresh-frozen plasma and platelets — you receive in blood transfusions. In 1985 American hospitals and blood banks began screening the blood supply for HIV antibodies. This blood testing, along with improvements in donor screening and recruitment practices, has substantially reduced the risk of acquiring HIV through a transfusion. In 1995, the chance of transfusion-associated transmission in the United States was about one in every 450,000 to one in every 600,000 units of blood transfused. In 2003, the estimated risk was one in 1.4 million to 1.8 million units.
• Transmission through needle sharing. HIV is easily transmitted through needles and syringes contaminated with infected blood. That's why sharing intravenous drug paraphernalia puts you at high risk of HIV and of other infectious diseases such as hepatitis. Your risk is increased if you inject drugs frequently or also engage in high-risk sexual behavior. Although avoiding the use of injected drugs is the most reliable way to prevent infection, this may not be an option for you. If so, one way to reduce your risk is to use household bleach to sterilize injection paraphernalia. Another option is to participate in a needle exchange program in your community. These programs allow you to exchange used needles and syringes for sterile equipment. Finally, consider seeking counseling or treatment for your drug use.
• Transmission through accidental needle sticks. Transmission of the virus between HIV-infected patients and health care workers through needle sticks is low. Experts put the risk at well less than 1 percent.
• Transmission from mother to child. Each year, nearly 700,000 infants are infected with HIV, either during pregnancy or through breast-feeding. But if women receive treatment for their HIV infection during pregnancy, the risk to their babies decreases greatly. Combinations of HIV drugs may reduce the risk of mother-to-child transmission even more. In the United States, most pregnant women are pre-screened for HIV, and anti-retroviral drugs are readily available. Not so in developing nations, where women seldom know their HIV status and treatment is often unavailable. But a new rapid test administered during labor that can show whether a woman has HIV in about an hour may make a big difference in poor countries.
• Other methods of transmission. In rare cases the virus may be transmitted through organ or tissue transplants or unsterilized dental or surgical equipment.

Ways HIV is NOT Transmitted

To become infected with HIV, infected blood, semen or vaginal secretions must enter your body. You can't become infected through ordinary contact — hugging, dancing or shaking hands — with someone who has HIV or AIDS. You also can't be infected in any of the following ways:

• Coming into contact with the sweat or tears of someone with HIV or AIDS.
• Sharing food, utensils, towels or bedding, a swimming pool, a telephone or a toilet seat with someone who has the virus.
• Being bitten by bedbugs or mosquitoes.
• Kissing someone who is HIV-positive or who has AIDS. There's no evidence that the virus is transmitted through kissing. Although HIV is sometimes found in the saliva of people with the virus, it occurs in low concentrations. In addition, natural inhibitory substances in saliva help prevent transmission of the virus.
• Donating blood. (Applies to US only)