"Long before it's in the papers"
April 28, 2009

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AIDS pandemic may be a century old

Oct. 1, 2008
Courtesy NIH/National Institute of 
Allergy and Infectious Diseases
and World Science staff

A new study sug­gests the most per­va­sive strain of HIV be­gan spread­ing among hu­ma­ns be­tween 1884 and 1924, not dur­ing the 1930s, as pre­vi­ously re­ported, re­search­ers say.

HIV is the vi­rus ac­cept­ed by sci­en­tists to cause AIDS.

The ear­li­er per­i­od of or­i­gin co­in­cides with the es­tab­lish­ment of cities in the west-central Af­ri­can re­gion where the ep­i­dem­ic of this HIV strain—HIV-1 group M—emerged, re­search­ers said.

The bas­ic struc­ture of the HIV vi­rus, which in­vades cells and causes AIDS. It is 1/10,000 of a mil­li­me­ter wide and glo­bu­lar . The out­er coat of the vi­rus, known as the vi­ral en­ve­lope (gray), is com­posed of two lay­ers of fat­ty molecules called lipids, tak­en from the mem­brane of a hu­man cell when a new­ly formed vi­rus par­t­i­cle buds from the cell. Em­bed­ded in the vi­ral en­ve­lope are pro­teins from the host cell, as well as around 72 cop­ies of a com­plex HIV pro­tein (fre­quent­ly called "spikes") that pro­trudes through the sur­face of the vi­rus par­t­i­cle. This pro­tein, known as Env, con­sists of a cap made of three molecules called gly­co­pro­tein (gp) 120, and a stem con­sist­ing of three gp41 molecules that an­chor the struc­ture in the vi­ral en­ve­lope. (Im­age cour­tesy NIAID)

A new study suggests the most pervasive global strain of HIV began spreading among humans between 1884 and 1924, not during the 1930s, as previously reported, scientists say. HIV is the virus accepted by scientists to be behind AIDS. The earlier period of origin coincides with the establishment of urban centers in the west-central African region where the epidemic of this particular HIV strain—HIV-1 group M—emerged, researchers said. This suggests urbanization and associated “high-risk” behaviors set the stage for the AIDS pandemic, they added. The research, led by Michael Worobey of the University of Arizona in Tucson, appears in the Oct. 2 issue of the research journal Nature. To reach the new estimate of the virus’ date of origin, a team of scientists screened tissue samples. In this way they claimed to have uncovered the world’s second-oldest genetic sequence of HIV-1 group M, dating from 1960. The investigators then used the sequence along with dozens of other previously known HIV-1 sequences to build a range of plausible family trees for this viral strain. The lengths of the tree branches represent the time it took for the virus to genetically diverge from its ancestors. The timing and number of these mutations let scientists gauge the likely range of rates at which the trees have grown—that is, the probable rates of evolution of the virus, they said. Based on this information, the scientists projected back in time to the period when the trees most likely took root: around the turn of the 20th century, they said. Using newly developed techniques, the scientists recovered 48-year-old HIV gene fragments from a wax-embedded lymph-node tissue biopsy from a woman in Kinshasa in Congo. The oldest known HIV-1 group M genetic sequence comes from a 1959 blood sample from a man also from Kinshasa. A comparison of the same genetic region in the 1959 virus and the 1960 virus provided additional evidence for the earlier date of origin, the scientists reported: this test revealed that the amount of genetic divergence between the sequences took more than four decades to evolve.