Human immunodeficiency virus infection and
acquired immune deficiency syndrome (
HIV/AIDS) is a spectrum of conditions caused by infection with the
human immunodeficiency virus (HIV). It may also be referred to as
HIV disease or
HIV infection. Following initial infection, a person may not notice any symptoms or may experience a brief period of
influenza-like illness. Typically, there is a prolonged period with no symptoms. As the infection progresses, it interferes more and more with the
immune system, making the person much more susceptible to common infections, like
tuberculosis, as well as
opportunistic infections and
tumors that do not usually affect people who have working immune systems. The late symptoms of the infection are referred to as
AIDS. This stage is often complicated by an infection of the lung known as
pneumocystis pneumonia,
severe weight loss, skin lesions caused by
Kaposi's sarcoma, or other
AIDS-defining conditions.