Scientists reported on Wednesday that they have recovered DNA from the oldest viruses known to have infected humans — and have succeeded in resurrecting some of them in the laboratory.

The viruses were all strains of hepatitis B. Two teams of researchers independently discovered its DNA in 15 ancient skeletons, the oldest a farmer who lived 7,000 years ago in what is now Germany.

Until now, the oldest viral DNA ever recovered from human remains was just 450 years old.

The research may provide clues to the continuing evolution of hepatitis B, a plague that infects an estimated 257 million people worldwide and contributes to an epidemic of liver cancer.

“It’s a hugely important moment in our understanding of one the most important pathogens of humans,” said Edward C. Holmes, a virologist at the University of Sydney.