The human immunodeficiency virus (HIV) is a virus that causes infection in humans. The human immunodeficiency virus (HIV) attacks the immune system, weakening people's defenses against a variety of illnesses and cancers that healthy immune systems can combat. Infected people become immunodeficient as the virus destroys and inhibits the function of immune cells. The CD4 cell count is commonly used to assess immune function. The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS), which, depending on the individual, can take many years to develop if not treated. The development of certain tumours, infections, or other serious long-term clinical symptoms is what defines AIDS. The acronym AIDS refers to acquired immunodeficiency syndrome. It is the last stage of HIV infection. It occurs when the body's immune system is severely harmed by a virus. AIDS does not affect everyone who has HIV.
A sexually transmitted disease (STD) is a condition that is spread from one person to another through sexual intercourse. By having unprotected vaginal, anal, or oral sex with someone who has the STD, a person can contract the disease. A sexually transmitted infection (STI) or venereal disease (VD) is another name for an STD.