Seven thousand years ago, in a valley that is today central Germany, a young man lay down to die. He was 25 or 30, and a farmer most likely. It is not known why he died young. But powerful genetic tools have now pulled out a tantalizing clue: the fragmented DNA of a virus that infected his liver all those millennia ago.
It is the oldest virus ever directly sequenced, opening up a new window onto prehistory. For the past decade or so, ancient human DNA from millennia-old teeth and bones has been revolutionizing the study of the past. More recently, DNA from ancient bacteria—such as leprosy and plague—in those same teeth and bones has done the same for the study of past epidemics. Viruses were always the next logical step. But their genomes are small and sometimes structured in a way that does not hold up well over time.
Until this week, no one had directly sequenced a virus more than a few hundred years old. And now—as a testament to how quickly the field of ancient DNA is moving—not one but two separate research groups report finding hepatitis B viruses in teeth several millennia old in Eurasia.
The first group, led by Ben Krause-Kyora and Johannes Krause in Germany, sequenced viruses from the 7,000-year-old man a well as a 5,000-year-old man and another 1,000-year-old man. Their work is reported in a preprint on bioRxiv, a site where researchers share early versions of papers that have not yet been peer reviewed. A second paper from another group of researchers led by Eske Willerslev at the University of Copenhagen, published in Nature, reports the hepatitis B sequences of 12 individuals ranging from the Bronze Age (2500 B.C.) to the Medieval period. Hepatitis B infects the liver, but it also enters the bloodstream, circulating through the body and winding up in bones and teeth, where it can be preserved.