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How AIDS Spread Across America

Researchers reconstruct origins of pandemic

Researchers at the University of Arizona and the University of Cambridge in the United Kingdom have reconstructed the origins of the acquired immune deficiency syndrome (AIDS) pandemic in unprecedented detail.

The findings were made possible by a new molecular technique that allowed the team to recover genetic material from more-than-40-year-old serum samples and to decipher the gene sequence of the human immunodeficiency virus (HIV) subtype that started the outbreak on the North American continent in the early 1970s. Phylogenetic analyses estimated the jump to the U.S. at about 1970 and placed the ancestral U.S. virus in New York City, strongly suggesting that this was the crucial hub from which HIV made its way across the continent. 

Insights gained from this study may help researchers and health officials better understand how pathogens move through populations and may lead to more-effective strategies aimed at reining in, or eradicating, dangerous pathogens, according to the authors. 

Published in Nature, the results confirm previous findings retracing the routes by which the virus entered and spread through the U.S. and eliminate any remaining doubts surrounding the Caribbean region as a key stepping-stone from which HIV jumped into the U.S.

While it had been established that HIV already was infecting people in the U.S. before 1981, the year AIDS was recognized, the timing and earliest movements of the virus in the U.S. were unknown until now.

By screening more than 2,000 serum samples collected from American men between 1978 and 1979, the researchers were able to recover eight near-full-length viral RNA genome sequences, representing the oldest HIV genomes in North America. This early, full-genome “snapshot” revealed that the U.S. HIV-1 epidemic showed extensive genetic diversity in the 1970s, but also provided strong evidence of its emergence from a pre-existing Caribbean epidemic.

Having the complete genomic information allowed the authors to tackle questions that had vexed researchers for decades—for example, how quickly the virus spread at different times in different locations. Once HIV had crossed the Atlantic from Africa, it quickly spread through the Caribbean and from there into the U.S.; and yet the epidemic went unnoticed until it hit this country. New York City turned out to be the most critical hub for the AIDS epidemic in the U.S., and the newly sequenced genomes showed that the virus must have arrived there in, or very near, 1970. From New York, HIV spread to San Francisco and, presumably, to other locations in California, where AIDS patients were first recognized in 1981.

Being able to look back in time and piece together what it took for the HIV pandemic to happen is encouraging, the researchers said.

“We can now look forward in time and really see a future in which—even if the virus is not completely eliminated—it could be driven down to no new transmission in large swaths of the world,” remarked lead investigator Dr. Michael Worobey.

Source: University of Arizona; October 26, 2016.

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