(2) viral disease Explanation: AIDS (Acquired immune deficiency syndrome or acquired immunodeficiency syndrome) is a disease caused by a virus called HIV (Human Immunodeficiency Virus). The illness alters the immune system, making people much more vulnerable to infections and diseases. This susceptibility worsens as the disease progresses. HIV is found in the body fluids of an infected person (semen and vaginal fluids, blood and breast milk).