AIDS (acquired immune deficiency syndrome) was first recognized in North America in the early 1980s. It is caused by a virus known as HIV (human immunodeficiency virus). HIV infection has become a worldwide epidemic.
HIV is more common among certain populations at risk, such as people who inject illicit drugs, and bisexual and gay men. HIV infections are also increasing among women, Aboriginal peoples, and African and Caribbean communities.
The virus can be found in the blood, semen, vaginal fluid, and breast milk of infected people. HIV is also found in saliva, sweat, and tears, though not in high enough amounts to transmit the virus to another person. There are no known cases of anyone catching HIV through sneezing, shaking hands, or from toilet seats or mosquito bites.
The two most common ways to be infected with HIV in North America are through unprotected sex and sharing needles. HIV may be transmitted through unprotected heterosexual or homosexual, vaginal, anal, or oral sex. Although the risk of infection is lower with oral sex, it is still important to use protection during oral sex, such as a dental dam (a piece of latex to cover the vagina during oral sex) or a condom. HIV can also be passed on through perinatal infection, where mothers who have HIV are at risk of giving the disease to the baby during birth. The risk of perinatal infection is declining with new treatments. Breast-feeding by an infected mother can also transmit HIV.
Once HIV enters the bloodstream, it takes over cells vital to the immune response, known as CD4+ lymphocytes. The virus then inserts its own genes into the cell, turning it into a miniature factory that produces more copies of the virus. Slowly, the amount of virus in the blood goes up and the number of healthy CD4+ cells goes down. The destruction of CD4+ cells interferes with the body's ability to fight off infections and other diseases.
Symptoms of HIV infection appear 2 to 12 weeks after exposure. At this point the virus begins rapidly taking over immune cells in the blood. The symptoms of this phase are flu-like and include:
When the symptoms begin to appear, the person with HIV is very infectious. The symptoms usually go away within a week to a month, and the person will feel fine again. However, the symptoms may return from time to time. The symptoms of HIV are similar to symptoms of other diseases. The only way to know for sure whether you are HIV-positive is to be tested. After infection with HIV, it can take 3 months for antibodies to the virus to be detectable in the blood. On average, it takes about 22 days to develop antibodies. This is called seroconversion. After seroconversion occurs, the virus can be detected using a blood test.
After the initial symptoms go away, the body's immune system tries to control the virus. The immune system can keep the virus at bay for a while, but it can't completely get rid of it. Many people will feel fine for years before their immune system weakens and they develop AIDS. Without treatment, about half of HIV-positive people develop AIDS within 10 years of infection. Some people develop AIDS within a few years of infection. A few, called long-term non-progressors, do not develop AIDS until much later. Many factors affect the timeframe to develop AIDS, including medications and the person's general health and lifestyle.
AIDS is a term applied to advanced HIV disease. AIDS is defined as having HIV and an opportunistic infection (an infection by a microorganism that ordinarily does not cause disease unless the immune system is weakened) normally associated with AIDS. These infections can be bacterial, fungal, viral, or parasitic. Examples of opportunistic infections include toxoplasmosis, pneumocystis pneumonia, cryptococcal meningitis, progressive multifocal leukoencephalopathy (PML), cryptosporidium, cytomegalovirus, and Mycobacterium avium complex (MAC). With the use of better medications to treat HIV, the risk of opportunistic infections has dropped over the years; however, people with AIDS will usually need to take medications (such as antibiotics) to prevent opportunistic infections.
People who have AIDS are also more likely to develop cancer, especially cancers of the immune system (lymphomas). Another cancer common for people with AIDS is Kaposi's sarcoma, a type of cancer that causes bluish red nodules on the legs and that spreads to the lymph system. Women with AIDS are prone to developing cancers of the cervix. Gay men with HIV have higher rates of infection by HPV, a virus linked to anal cancer, and precancerous HPV strains.
Children with AIDS tend to get common childhood infections like conjunctivitis, otitis media, and tonsillitis, but they experience symptoms much worse than the infection usually causes.
Excessive weight loss or "wasting syndrome" is a problem for approximately 20% of people who have HIV infection. It is associated with an unexplained loss of 10% or more of normal body weight, plus chronic diarrhea (30 days or more) or chronic weakness with fever (30 days or more).
Most people with AIDS die from the diseases that AIDS makes them more susceptible to. The virus occasionally infects the brain, causing dementia that gets worse over time.