How cold sores could unlock the mystery of human migration: Mutation of herpes virus mirrors movement of ancestors out of Africa

Most genetic diversity found in African strains of the cold sore virus

Pattern matches movement of human genome that gradually spread outwards from the continent to Asia and Europe

Researchers hope the technique could also help explore why certain strains of a virus are so much more lethal than others

If you want to unlock the mystery of how humans migrated from Africa, then the unsightly cold sore could provide the answer.

The different genome variations in the cold sore virus have been hitchhiking their way around the world for tens of thousands of years.

Tracking these variations is part a project by the University of Wisconsin at Madison who has been analysing 31 samples of herpes simplex virus type-1.

When the researchers compared the strains of HSV-1 collected in North America, Europe, Africa and Asia, they were 'stunned' by the results.

The map shows how the cold sore virus originated in Africa and gradually spread outwards, evolving along the way. Different variants (labelled as 'I', 'II', 'III', 'V' etc) in the herpes virus have been hitchhiking their way around the world for tens of thousands of years and mirror the theory of how man populated the world

WHAT IS THE 'OUT OF AFRICA' THEORY OF HUMAN MIGRATION?

The Out of Africa theory is the most widely accepted model describing the geographic origin and early migration of modern humans. Studies of human genomes have shown that our ancestors emerged from Africa roughly 150,000 to 200,000 years ago, and then spread eastward toward Asia, and westward toward Europe. These settlers replaced other early humans (such as Neanderthals), rather than interbreeding with them.

Their analysis showed the most genetic diversity was found in African strains of the virus, suggesting it had the oldest roots.

The results give weight to the proposed by the ‘Out of Africa’ theory of human migration.

‘The viral strains sort exactly as you would predict based on sequencing of human genomes,’ said senior author Curtis Brandt, a professor of medical microbiology and ophthalmology.

‘We found that all of the African isolates cluster together, all the virus from the Far East, Korea, Japan, China clustered together, all the viruses in Europe and America, with one exception, clustered together.’

The researchers compared the strains of the herpes simplex virus (pictured) which were collected in North America, Europe, Africa and Asia

Geneticists explore how organisms are related by studying changes in the sequence of bases, or ‘letters’ on their genes.

From knowledge of how quickly a particular genome changes, they can construct a ‘family tree’ that shows when particular variants had their last common ancestor.

Studies of human genomes have shown that our ancestors emerged from Africa roughly 150,000 to 200,000 years ago, and then spread eastward toward Asia, and westward toward Europe.

The findings reflect the view that a small human population passed through a ‘bottleneck’ to get from Africa to the Middle East.

From there, they went their separate ways to Europe and Asia, and eventually to the Americas.

Nearly all of the samples from the U.S. were linked to European strains, but one sample from Texas was linked to Asia.

Brandt claims that the sample may have come from someone who picked up the virus during a trip to the Far East.

Studies of human genomes have shown that our ancestors emerged from Africa roughly 150,000 to 200,000 years ago

Another theory is that the person picked it up from someone with Native American heritage whose ancestors passed over a ‘land bridge’ between Asia and North America.

‘We found support for the land bridge hypothesis, because the date of divergence from its most recent Asian ancestor was about 15,000 years ago,’ Professor Brandt said.

‘The dates match, so we postulate that this was an Amerindian virus.’

The researchers said HSV-1 strains are ideal for tracking long-term migration patterns because they're easy to collect and capable of forming lifelong latent infections.

Because the viral genome is so much simpler than the human genome, it's cheaper to sequence.

‘While preliminary, our data raise the possibility that HSV-1 sequences could serve as a surrogate marker to analyse human migration and population structures,’ the researchers said.

The technology of simultaneously comparing the entire genomes of related viruses could also be useful in exploring why certain strains of a virus are so much more lethal than others.

In a tiny percentage of cases, for example, HSV-1 can cause a deadly brain infection, Brandt notes.

‘We'd like to understand why these few viruses are so dangerous, when the predominant course of herpes is so mild.