Washington, Oct 2 : The most pervasive global strain of HIV began spreading in humans around 1900 in sub-Saharan Africa, according to a new research.
The research found that HIV began spreading between 1884 and 1924, around the same time urban centres in west central Africa were established. This estimated time of origin is decades earlier than the previous estimate of 1930.
This suggests that the growth of cities and associated high-risk behaviours may have been a principal cause of the rapid spread of the virus, reports Nature.
To find the point of HIV's origin, a team of scientists, led by Michael Worobey, D. Phil., of the University of Arizona in Tucson, screened multiple tissue samples and uncovered the world's second-oldest genetic sequence of HIV-1 group M, which dates from 1960.
The researchers then used it along with dozens of other previously known HIV-1 genetic sequences to construct a range of plausible family trees for this viral strain.
The lengths of the tree branches represent the periods of time when the virus genetically diverged from its ancestors.
The timing and number of these genetic mutations enabled the researchers to calibrate the probable range of rates at which the trees have grown-that is, the probable rates of evolution of HIV-1 group M.
Based on this range of rates, the researchers projected back in time to the period when the trees most likely took root: around the turn of the 20th century. This marks the probable time of origin of HIV-1 group M, according to the researchers.
Using newly developed techniques, the researchers recovered the 48-year-old HIV gene fragments from a wax-embedded lymph-node tissue biopsy from a woman in Kinshasa in the Democratic Republic of the 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 that their common ancestor existed around 1900.
The comparison revealed that the amount of genetic divergence between these two HIV sequences took more than 40 years to evolve.
The study is published in the current issue of Nature.