Persons who are infected with HIV may not know it. Some people experience flu-like symptoms, such as fever, headache, muscles and joints, stomachache, swollen lymph glands or a skin rash that lasts one to two weeks.
The virus multiplies in the body for a few weeks or even months before the immune system responds. During this time a person will not test positive for HIV infection but does have the ability to infect others.
The virus uses CD4 T cells, a type of white blood cell that fights infection, to make copies of itself. This process destroys the CD4 T cells, weakening the immune system. Without treatment, a person might experience fevers, night sweats, diarrhea or swollen lymph nodes for several weeks.
HIV progresses to AIDS when:
- An HIV-infected individual's CD4 T cell count drops below 200 cells/mm
- An HIV-infected individual develops an illness that is very unusual in someone who is not HIV-positive
Opportunistic illnesses that are typical of AIDS include:
- Pneumocystis carinii pneumonia, a lung infection
- Kaposi's sarcoma, a skin cancer
- Cytomegalovirus, an infection that usually affects the eyes
- Candida, a fungal infection that can cause thrush, a white film and infections in the throat or vagina
- Invasive cervical cancer
AIDS-related diseases also include serious weight loss and brain tumors.
AIDS varies from person to person. Some people die soon after getting infected while others live relatively normal lives for many years, even after being officially diagnosed with AIDS.
Causes and Risk Factors
AIDS is caused by infection with HIV. HIV infection has been the only common factor shared by persons with AIDS throughout the world, regardless of sexual preferences, lifestyle, health, sexual practices, age or gender.
While much still needs to be learned about HIV and AIDS, certain factors can put a person at higher risk of acquiring it, including:
- Exposure to HIV infected body fluids, including blood, semen, vaginal fluid, breast milk or other fluids that usually only present a risk to healthcare workers (cerebrospinal fluid surrounding the brain and spinal cord, synovial fluid surrounding bone joints and amniotic fluid surrounding a fetus)
- Sharing of needles or syringes with someone who is infected
- Being born to or breast-fed by a woman who is HIV-positive
- Not practicing safer sex (use of a latex condom)
HIV does not reproduce outside of a living host, nor does it survive well in the environment. It cannot be spread through casual contact, such as occurs in offices, business settings or even most homes. There is no evidence that it can be spread through insects.
It is not yet known what the origins of the HIV virus are. The earliest known case of HIV was from a blood sample collected in 1959 from a man in the Democratic Republic of Congo. The virus has existed in the United States since at least the mid- to late-1970s.
In 1983 scientists isolated HIV-1. Three years later, a second type, HIV-2, was isolated from AIDS patients in West Africa. Both spread the same way, but HIV-2 appears to develop more slowly, be milder and have a shorter period of time when it is infectious compared to HIV-1. HIV-2 is rare in the United States.
While receiving donated blood or transfusions used to be a source of HIV infection, all U.S. blood donations have been tested for a combination of HIV-1 and HIV-2 since 1992.