Used in trial and released November 15 in the Proceedings of the National Academy of Sciences, the maps are relevant not only as tools of criminal justice, but demonstrations of the extraordinary detail made possible by genetic analysis.

“Until this finding, you could make statements about which viruses were more closely related to one another, but you didn’t know the direction of transmission” when comparing viral samples, said geneticist Michael Metzker of the Baylor College of Medicine. “You could only go so far in describing transmission dynamics. We went one step further in proposing the index case.”

The gene-crunching tools used by Metzker’s team were relatively old-fashioned, and the scientists had performed similar analyses before, in the case of another intentional HIV transmission. But in that study, they knew who the samples came from, raising questions about whether they already knew what to look for.

In the new study, the researchers did not know the identity of HIV samples from Anthony Whitfield of Olympia, Washington or Philippe Padieu of Collin County, Texas. Neither did they know which samples came from six women who in 2004 charged Whitfield with intentionally infecting them with HIV, nor from six women who in 2009 charged Padieu with the same crime.

Metzker’s team compared relationships between the different HIV strains, each of which was subtly different because the virus mutates so rapidly that it can change between transmission events. Despite the changes, the viruses pointed back to common sources.

Metzker’s team is far from the first to perform phylogenetic analyses, but rarely is the data so complete. According to Metzker, similar approaches will be useful in many fields.

“It’s not restricted to HIV. It could be used in the identification of food-borne diseases where identifying the source of contamination could be very important,” he said. “It could be used in identifying sources of biological weapons, if you’re trying to pinpoint where an outbreak is taking place. It has lots of applications beyond HIV cases.”

Image: Phylogenetic trees of HIV infections traced to their original source./PNAS.

See Also:

• Mapping HIV Genome’s Shape, Not Just Sequence
• HIV Evolution Outpaces Vaccines
• A New Tactic Against HIV: T-Cell Tweaks
• Ancient Fossil Flower Is Father of Sunflower Family

Citation: “Source identification in two criminal cases using phylogenetic analysis of HIV-1 DNA sequences.” By Diane I. Scaduto, Jeremy M. Brown, Wade C. Haaland, Derrick J. Zwickl, David M. Hillis, and Michael L. Metzker. Proceedings of the National Academy of Sciences, Vol. 107 No. 46, November 16, 2010.

Brandon’s Twitter stream, reportorial outtakes and citizen-funded White Nose Syndrome story; Wired Science on Twitter.

Authors: Brandon Keim

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