Most Kaposi's sarcoma is now believed to be caused by a virus called Human Herpes Virus 8 (HHV8), which is also known as Kaposi’s Sarcoma-associated Herpes Virus (KSHV). It can affect people with a weakened immune system, including people with HIV (Human Immunodeficiency Virus) and Aids.
HHV8 is mainly spread through saliva, but can also be spread in blood and semen, or from a mother to her unborn child. The virus can be passed on through sexual contact, kissing, blood transfusions and organ transplantation.