Scientists reveal criminal virus spreaders using evolutionary forensics

November 15, 2010

The source of HIV infection in two separate criminal cases in which men were convicted of intentionally infecting their female sexual partners was confirmed by scientists from The University of Texas at Austin and Baylor College of Medicine using evolutionary forensics.

The research shows it's possible to identify the source of a cluster of diseases by analyzing the evolution of a virus within its host and between individuals. This type of research is known broadly as phylogenetic analysis.

In the cases, State of Washington vs. Anthony Eugene Whitfield and State of Texas vs. Philippe Padieu, it was shown that Whitfield and Padieu knowingly spread to multiple female partners through unprotected sex.

Dr. David Hillis, Dr. Mike Metzker and their graduate students were able to pinpoint these two origins of the women's infections from blind (identities unknown to them) .

"Our research demonstrates that the source of a cluster can be identified through phylogenetic analysis," said Hillis, the Alfred W. Roark Centennial Professor at The University of Texas at Austin. "This kind of analysis can and has been used both to exonerate the falsely accused as well as evidence in convictions."

The scientists published their results in PNAS Early Edition the week of November 15.

HIV evolves rapidly within infected individuals over the course of a few months, so the viruses cannot be compared between a source and a newly infected individual for an exact match. It's not as easy as directly comparing two individuals' DNA to confirm paternity.

Even two samples of HIV from the same person, taken several months apart, will be different because the virus is evolving so quickly.

"Within a given person, there is not just one strain but a population of strains because HIV mutates all the time when it makes new virions ()," said Metzker, associate professor at Baylor. "During transmission, however, there is a genetic bottleneck in which only one or two viruses get transmitted to the recipient."

In order to understand the origins of the infections of the women victims, therefore, the scientists needed to reconstruct the evolutionary history of the viruses.

To do so, Metzker's lab at Baylor College of Medicine first isolated and sequenced the HIV genes from blind blood samples taken from the accused, from the victims and from other HIV positive individuals who lived in the same area as the victims and the accused.

Metzker sent the gene sequences (still blind to identity) to the Hillis lab at The University of Texas at Austin, where they constructed evolutionary histories for the viruses by performing the phylogenetic analysis.

In each of the cases, they identified the sample from the unknown individual that shared the subsets of HIV genes that were related to the other individuals in the case.

"This individual was the only person who could have infected the others," said Hillis.

In each case, the source individual was revealed at the trial to be the defendant when the blinded code numbers on the blood sample were revealed to the court.

"We didn't know that information until the trial," said Hillis. "We just new that we had identified the only person whose HIV population was consistent as the source of the multiple infections."

Hillis served as an expert witness in Washington vs. Whitfield and worked on the forensic analysis for Texas vs. Padieu. In neither case was he called to testify. He did testify in a landmark trial in 1998, the State of Louisiana vs. Richard J. Schmidt, about the use of phylogenetic analysis in viral transmission cases.

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not rated yet Nov 15, 2010
While I get how this technique clearly shows that the male was responsible for transmitting the virus to the two female's, I'm not clear how this proves that the transmission was INTENTIONAL.
not rated yet Nov 15, 2010
While I get how this technique clearly shows that the male was responsible for transmitting the virus to the two female's, I'm not clear how this proves that the transmission was INTENTIONAL.

Even if it was intentional, is it illegal? It is definitely immoral, but do we actually have laws prohibiting this type of biological warfare? Perhaps someone better versed can comment on this. It seems that I am free to spread the flu to whoever I want and if they die from complications I couldn't be implicated. Are we really considering HIV and other diseases as a weapon when charging people with assault? Yes, this guy is a jerk, but these women should have used condoms if they were unsure of his past sexual history, unless they were raped of course. Again, I'm not defending him, I'm just curious about the legal stance.
not rated yet Nov 16, 2010
i would think its illegal to knowingly expose people to grave danger/harm, but you flu argument is most interesting, apperently we do not consider the flu as grave as hiv, while certainly people die every year from the flu, however, its kind of very hard to put everybody with the flu in a balloon the economy and soceity would come to a halt, while transmission of hiv requires a very specific mode of operation that the transmitter could choose to avoid, while its very hard not to sneeze or touch any doorknobs when you have the flu
not rated yet Nov 16, 2010
The guy was probably tested and knew he was HIV positive prior to infecting these women... So, there is intention in the act. People that die from the flu are usually immunodeficient, it's usually not a deadly infection. HIV, on the other hand, is usually very deadly (without treatment), and can seriously affect a person's quality of life, their entire life, with and without treatment. If someone with the flu, knowing they had the flu, intentionally got someone immunodeficient sick, knowing they were immunodeficient, then there would likely be some legal liability involved.

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