A new study of herpes virus reconfirmed widely held beliefs that human migration spread out from Africa.
A new study on herpes virus confirmed the widely held belief that the human genome spread "out of Africa." Researchers examined strains of herpes simplex virus type 1 that were collected across Europe, North America, Asia and Africa. On thoroughly examining the virus' genome, researchers detected ample evidence of the "out of Africa" model of human migration. According to this model, early humans first emerged in Africa before migrating to different parts of the world in disparate groups.
"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 the virus from the Far East, Korea, Japan, China clustered together, all the viruses in Europe and America, with one exception, clustered together," Curtis Brandt, professor of medical microbiology at the University of Wisconsin-Madison and senior author of the study, said in a statement.
"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."
With the help of high-capacity genetic sequencing, researchers of the study were able to create a "family tree" for the virus. The construction of a family tree helps geneticists better understand how fast a genome changes. The tree began in Africa about 150,000 to 200,000 years ago, bottlenecked in the Middle East and finally spread to Europe, the Americas and Asia. Though previous researches have been conducted on herpes simplex virus type 1, only single genes or a small cluster of genes were studied. According to Brandt, this approach is not sufficient to provide accurate results.
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.
"We'd like to understand why these few viruses are so dangerous, when the predominant course of herpes is so mild. We believe that a difference in the gene sequence is determining the outcome, and we are interested in sorting this out," he said.
The HSV 1 strain was ideal for the study due to various reasons. Firstly, it is rarely fatal and sticks with the host for life. Moreover, since it is spread through close contact like kissing, it is likely that the same strains will be found in all family members. It is also much smaller and simpler to work with than the full human genome, but still large enough to provide meaningful data.
Another interesting find of the study is that it provides evidence suggesting Native Americans are descended from Asian peoples who crossed a land bridge from far eastern Siberia into the Americas thousands of years ago.
All but one virus sample collected in the United States matched European strains. The one that didn't match was a Texas-based strain that bore strong resemblances to Asian strains. Brandt says that this is likely due to immigration across a Bering Strait land bridge more than 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 says. "The dates match, so we postulate that this was an Amerindian virus."
The study was published in PLOS One.
