HIV or the Human Immunodeficiency Virus is a virus that only infects humans.
A person diagnosed with HIV infection is referred to as being HIV positive.

Once HIV enters the bloodstream, it inserts itself into the cells that make up the immune system and then begins to multiply. The HIV virus attacks the immune system slowly making it easier for a person to get a variety of illnesses known as opportunistic infections. In some cases it may take years for a person to start feeling and looking ill as a result of being HIV positive. During this symptom-less or ‘asymptomatic period’, an HIV positive person can still infect others with the disease.