UNITED NATIONS, June 10 (Reuters) - The United Nations' top official in the global fight against AIDS, Peter Piot, is stepping down after 13 years, U.N. Secretary General Ban Ki-moon said on Tuesday.

Ban, in a speech before the 2008 High Level Meeting on HIV/AIDS, praised Piot for being a "tireless leader who has been at the vanguard of the response to AIDS since the earliest days of the epidemic."

A successor has not yet been named. Piot, a Belgian who co-discovered the Ebola virus in Zaire in 1976, has led the UN's response to the AIDS epidemic as executive director of the Joint U.N. Program on HIV/AIDS (UNAIDS) since its inception in 1995.

In a little noticed statement in April, Piot said he would step down when his term ended at the end of this year.

Globally, an estimated 33.2 million people are infected with the human immunodeficiency virus (HIV) that causes AIDS and 25 million have died so far from the fatal and incurable disease. (Reporting by Daniel Bases; Editing by Cynthia Osterman)

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