AIDS is caused by the human immunodeficiency virus (HIV), a virus that infects certain cells throughout the body. Most significantly, HIV infects white blood cells of the immune system and causes a gradual deterioration of immune function. During the course of infection, crucial immune cells called CD4+ T cells are disabled and killed, and their numbers progressively decline. These cells play a crucial the role of helping clear disease-causing substances from the body by signaling other cells in the immune system to perform their special functions. After the virus inserts itself into the host cell, it prevents the host cell from carrying out its natural functions and turning it into an HIV virus "factory".
Acquired Immunodeficiency Syndrome (AIDS) is not a single distinct disease, but rather a disorder characterized by a severe suppression of the immune system. This immunodeficiency renders the body susceptible to a variety of normally manageable infections, cancers, and other diseases.
AIDS is the name given to a late stage of HIV infection, during which there is evidence of significant impairment to the immune system. Because the illness is best understood as a continuum from initial infection to, in many cases, death, the term "HIV/AIDS" is frequently used.
You might not know if you get infected by HIV. Some people get fever, headache, sore muscles and joints, stomach ache, swollen lymph glands, or a skin rash for one or two weeks. Most people think it's the flu. Some people have no symptoms. The Body has more information on the early stage of HIV infection.
The virus will multiply in your body for a few weeks or even months before your immune system responds. During this time, you won't test positive for HIV, but you can infect other people.
When your immune system responds, it starts to make antibodies. When this happens, you will test positive for HIV.
After the first flu-like symptoms, some people with HIV stay healthy for ten years or longer. But during this time, HIV is damaging your immune system.