The virus that causes herpes simplex has plagued man for a long time. So long, in fact, that researchers were able to sequence its genetic code to confirm that it follows the “out-of-Africa” pattern of human migration.
The herpes simplex virus type 1 (HSV-1), usually causes nothing more severe than cold sores around the mouth, but it is very common with some 90 percent of American adults having been exposed.
Researchers compared 31 strains of HSV-1 collected in North America, Europe, Africa and Asia, and "the result was fairly stunning," said Curtis Brandt, a professor of medical microbiology and ophthalmology at University of Wisconsin-Madison
"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, all of the virus from the Far East, China, Japan, Korea, clustered together, all the viruses in Europe and America, with one exception, clustered together," he 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."
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 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. This paralleled existing analyses of human migration.
The new analysis could even detect some intricacies of migration. Every HSV-1 sample from the United States except one matched the European strains, but one strain that was isolated in Texas looked Asian. Either the sample had come from someone who had travelled from the Far East, or it came from a Native American whose ancestors 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. Brandt said. "The dates match, so we postulate that this was an Amerindian virus."
Herpes simplex virus type 1 was an ideal virus for the study because it is easy to collect, usually not lethal, and able to form lifelong latent infections. Because HSV-1 is spread by close contact, kissing or saliva, it tends to run in families. "You can think of this as a kind of external genome," Brandt said.
The results were published in the journal PLOS ONE.