What are the various routes by which transmission of human immunodeficiency virus takes place?

Explanation

AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human immunodeficiency virus (HIV).
It has the following modes of transmission:
Unprotected sexual contact with an infected person.
Transfusion of blood from a healthy to an infected person.
Sharing infected needles and syringes.
From an infected mother to a child through the placenta.