The genome sequences of 137 ancient humans who lived between about 1,500 and 4,500 years ago are reported in Nature this week. In a second Nature paper, analysis of these genomes and those of 167 Bronze Age humans reveals evidence of hepatitis B virus (HBV) in 25 of the 304 individuals. The findings suggest that humans throughout Eurasia were infected with HBV for thousands of years.
Eske Willerslev and colleagues sequenced the genomes of 137 ancient humans from the Eurasian steppes - a vast region spanning about 8,000 km from Hungary to northeastern China - covering a period of about 4,000 years. They also studied genomic data from 502 individuals from present-day self-reported ancestries across Central Asia, Altai, Siberia and the Caucasus. The findings shed light on the population history of the region, suggesting a gradual transition from Bronze Age pastoralists of Eurasian ancestry towards mounted warriors with primarily East Asian ancestry.
In the second paper, Willerslev and co-authors analysed ancient DNA sequences from 304 central and western Eurasian humans, who lived between about 200 and 7,000 years ago. They report evidence of HBV infections in 25 individuals, spanning a period of almost 4,000 years. The authors recovered 12 full or partial HBV genomes - including genotypes that are now extinct - that they analysed together with contemporary human and non-human primate HBV genomes. They show the existence of ancient HBV genomes in regions incongruent with their present-day distribution, and at least one now-extinct genotype.
Approximately 257 million people worldwide are chronically infected with HBV, and around 887,000 people died from associated complications in 2015, but the origin and evolution of the virus have remained unclear. Discovery of further ancient viral sequences may provide a clearer picture of the true origin and early history of HBV, and aid the understanding of the contributions of natural and cultural changes to disease burden and mortality.