AIDS is a disease caused by HIV infection which damages the immune system of an organism. It is a communicable disease and transmited by following ways:
1. Transfusion (transferring blood from one person to another) of HIV+ blood causes HIV infection to the healthy person.
2. Use of HIV infected instruments like syringes, needles, surgical and dental instruments spread the disease.
3. HIV infected mother spreads the disease to her child during pregnancy.
4. The body fluids like semen, blood, secretion of uterus contains high amount HIV. Direct contact (having sexual relationship) with these fluids causes HIV.