AIDS ( Acquired Immune Deficiency Syndrome ) is caused by the HIV ( Human Immunodeficiency Virus ) which attacks the white blood cells leading it unable to defend the body against diseases , weakening immune system. HIV is transmitted through sexual intercourse with an infected partner , blood transfusion if donor is infected , sharing of needles with an infected person and infected mother to baby. Some signs and symptoms to look out for AIDS is severe weight loss , chronic diarrhoea and fever , lung infections , kaposi's sarcoma ( a type of cancer ) and brain infections