Scanning electron microscope shows HIV proliferation (in green) Photo via CDC
No man is an island, but evolutionarily, each person functions like one for the HIV virus. That's according to Thomas Leitner, a researcher working on a project aimed at creating technology for tracking HIV through a population. The technology, which is being studied at the Los Alamos National Laboratory, may allow people to identify who infected them with the virus, a development that could have major implications in criminal proceedings.
“If you’re familiar with Darwin’s finches, you have a population of birds on one island and they keep moving and evolving as they spread to other islands so that each population is a little different,” Leitner said. “With HIV, it’s the same. Every person infected with HIV has a slightly different form the the virus. It’s the ultimate chameleon because it evolves this way.”
Those evolutionary changes and mutations are one of the reasons why the virus has been so difficult to develop a vaccine for. But it also allows researchers like Leitner to track its spread throughout a population. Each time it mutates, that mutation is encoded in the virus’ nucleus and creates a history of where that particular HIV strain has been before.
It’s called phylogenetics, and it’s a field that often studies how certain organisms are related to each other and when they diverged on the evolutionary tree. But it can also be used within a virus like HIV to establish connections between strains that differ slightly. It can also help researchers pinpoint exactly when a person was infected, something that diagnosis dates are often not useful for because of the sometimes long lag times between infection and diagnosis.
Leitner’s team at the Los Alamos National Laboratory has developed a computer model that can show the “actual, rapid evolution of the virus within each patient’s body.” That model is useful for determining how the virus, for instance, made its way from Latvia’s gay community, to intravenous drug users and eventually became embedded in the heterosexual population. But it’s also good at making the connection between strains that any two people might have.
“On the individual level, we’re working on forensic investigations relevant to criminal systems, trying to see who infected whom,” he said.
To make that connection, of course, the laboratory would need samples of the virus from both individuals if criminal activity is suspected. A national database of HIV-positive people and their viruses would also be a useful, if not hugely invasive and illegal tool. Los Alamos, however, already does have a database of (anonymized) HIV viruses that can be used for research.
HIV forensics is something that’s increasingly showing up in courts worldwide. In September, a man was arrested for allegedly having unprotected sex with more than 300 people without disclosing that he was HIV positive. In Canada, a man named Johnson Aziga was convicted of two counts of murder for transmitting the virus to two women who later died from the disease. The Supreme Court of Canada ruled that, because he did not tell the women he was HIV positive, he was guilty of fraud and could be charged with murder.
In the United States, more than 30 states have laws on the books that make it illegal to recklessly expose someone else to the virus, however the Obama administration has come out against the practice, because many of the laws criminalize behavior such as spitting by people who are HIV positive.
“While we understand the intent behind such laws, they may not have the desired effect and they may make people less willing to disclose their status by making people feel at even greater risk of discrimination,” the administration wrote in a 2010 policy paper. “In some cases, it may be appropriate for legislators to reconsider whether existing laws continue to further the public interest and public health.”
A paper published last month in the Journal of Infectious Diseases by researchers at Stanford University suggested that phylogenetics alone likely won’t be enough to determine transmission sequences. That paper cautioned that more information—such as contact tracing, the social networking of infected people—is needed to determine who infected whom.
“The notion that [genetic] sequences alone can identify specific transmission events between individuals is a misconception that has the potential to jeopardize the continued public benefit that results from the open publication of pathogen genomes,” the paper said. “Hypotheses about direct transmission, therefore, make sense only when sequence analysis is combined with contact tracing. Few studies, however, contain both contact data and HIV-1 sequence data, and those that do have been too small to provide insight into the population-level factors responsible for HIV-1 spread.”
Leitner says that, though determining whether the strains of two people’s HIV viruses were related, his lab is one of the few trying to find a definite history of transmissions.
“There’s some outstanding questions. We can’t say unambiguously who infected who. It’s unclear whether we could have said A infected B or A infected X who infected B,” he said. “We can only say whether they’re linked compared to some control group. There’s still things we don’t quite understand, but those remaining questions are what we’re working on.”