The virus under study, herpes simplex virus type 1 (HSV-1), usually causes nothing more severe than cold sores around the mouth, said Curtis Brandt, senior author of the study and a professor of medical microbiology and ophthalmology at University of Wisconsin–Madison. (Agencies)
Brandt and co-authors Aaron Kolb and Cecile Ane compared 31 strains of HSV-1 collected in North America, Europe, Africa and Asia.
"The viral strains sort exactly as you would predict based on sequencing of human genomes. We found that all of the African isolates cluster together, the entire virus from the Far East, Korea, Japan and China clustered together, all the viruses in Europe and America, with one exception, clustered together," Brandt said.
"What we found follows exactly what the anthropologists have told us, and the molecular geneticists who have analyzed the human genome have told us, about where humans originated and how they spread across the planet," he said.
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.
In the new study, published in the journal PLOS ONE, researchers broke the HSV-1 genome into 26 pieces, made family trees for each piece and then combined each of the trees into one network tree of the whole genome. It was this grouping that paralleled existing analyses of human migration.
The new analysis could even detect some intricacies of migration. Every HSV-1 sample from the US except one matched the European strains, but one strain that was isolated in Texas looked Asian.
"How did we get an Asian-related virus in Texas?" Kolb said. Either the sample had come from someone who had travelled from the Far East, or it came from a Native American whose ancestors had crossed the "land bridge" across the Bering Strait roughly 15,000 years ago.
"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. The dates match, so we postulate that this was an Amerindian virus," Brandt said.
"Our results clearly support the anthropological data, and other genetic data, that explain how humans came from Africa into the Middle East and started to spread from there," Brandt said.
In the virus, as in human genomes, a small human population entered the Middle East from Africa.
"There is a population bottleneck between Africa and the rest of the world; very few people were involved in the initial migration from Africa," Brandt said.
"When you look at the phylogenetic tree from the virus, it's exactly the same as what the anthropologists have told us," he said.
The virus under study, herpes simplex virus type 1 (HSV-1), usually causes nothing more severe than cold sores around the mouth, said Curtis Brandt, senior author of the study and a professor of medical microbiology and ophthalmology at University of Wisconsin–Madison.