Impact, 14 October 2002, DNA analysis cracks HIV case

A genetic finding, that reads like a Hollywood script, analysed a woman's particular strain of HIV, thereby helping to convict her ex-boyfriend on charges of attempted-murder.

The case involved a woman who became infected with HIV in 1995 when Dr Richard Schmidt injected her with blood products extracted from one of his HIV-positive patients.

Researchers led by Dr Michael Metzker of Baylor College of Medicine in Houston, Texas, found that the woman's virus matched the victim's by analysing two genes present in the strains found in both, and compared them to those in other strains of HIV.

While the use of such forensic evidence in the courtroom is not new, pinning down the source of an HIV infection is quite tricky. The virus mutates so rapidly that researchers had to track the evolutionary changes in the DNA to link the woman's virus to the source.

The woman, a nurse, had no history any needle-stick injuries, but had been given an injection by Schmidt during an argument.

Investigators searched the doctor's office and found a record of Schmidt drawing his patient's blood around the same time the argument occurred with his girlfriend.

First time method used in court

The case is the first time that "phylogenetic analysis" - a study of the mutation rate of an organism - has been used in a court of law, according to Dr David Hillis of the University of Texas in Austin and colleagues.

This case demonstrates that it is now possible to trace the pathway of infections of viruses among individuals within a population, Hillis said.

In the case of Schmidt's girlfriend, the direction of transmission is clear. Not only could the investigators tell that the girlfriend and patients were connected in their infection history, but also that the patient contracted the virus first, before the infection was passed on to the victim.

Metzker and his team presented their findings in the Proceedings of the National Academy of Sciences Early Edition.

Various uses some potentially dangerous

According to Hillis, investigators may also use this method to find the origin of attacks by bioterrorists. In fact, a similar type of analysis was used to locate the origin of the strains of anthrax mailed last year in America.

Tracking the changes in viruses as they travel from one host to another may also help scientists predict how the virus will mutate in the future, allowing them to be one step ahead when developing vaccines, the researcher added.

One use for this analysis method however that could create problems, would involve pinpointing individuals who infected others unintentionally, thereby establishing blame.