Origin of HIV is about 100 years old

U.S.-led scientists estimate the human immunodeficiency virus began spreading between 1884 and 1924, about 30 years earlier than prior estimates. Led by University of Arizona Assistant Professor Michael Worobey, the researchers discovered the world's second-oldest genetic sequence of a strain of HIV known as HIV-1 group M. The sequence was recovered from a lymph-node tissue biopsy taken in 1960 from a woman in the Democratic Republic of the Congo.

The oldest known HIV-1 group M genetic sequence is from a 1959 blood sample of a man also from central Africa. The scientists said a comparison of the 1959 virus and the 1960 virus led them to conclude the genetic divergence between the HIV sequences required more than 40 years.

The researchers said they also used other HIV-1 genetic sequences to estimate probable rates of the evolution of the HIV-1 group M strain. According to their calculations, HIV began spreading among humans between 1884 and 1924 -- about the same time large urban population centers were being established in west-central Africa. That, said the scientists, is also the region where the HIV-1 group M strain is thought to have emerged.

The study appears in the journal Nature.