The measles virus diverged from a closely related cattle-infecting virus in approximately the sixth century BCE - around 1,400 years earlier than current estimates - according to a new study of dozens of measles genomes. The results paint a new portrait of the evolutionary history of the measles virus, showing that the pathogen emerged far earlier than previously suspected and at a time that coincided with the rise of large urban centers throughout Eurasia and South and East Asia. As one of humanity's oldest microbial foes, the measles virus has been a prime target for both health authorities and scientists seeking to define the evolutionary paths of common human pathogens. Researchers suspect that the measles virus emerged when the now-eradicated rinderpest virus spilled over from cattle into human populations. The accepted consensus dates the emergence of measles to around the end of the ninth century CE, but uncertainty still remains. To get a better fix on the origins of measles, Ariane Düx and colleagues reconstructed the measles virus genome using lung samples collected from a 1912 measles case. They then compared sequencing data to a 1960 measles genome, 127 modern measles genomes, and genomes from rinderpest and another cattle virus named PPRV. Using a series of evolutionary and molecular clock models, the researchers traced the emergence of measles in humans between the years 1,174 BCE and 165 CE, with a mean estimate of 528 BCE. The authors speculate that their results support a scenario where a bovine virus ancestor circulated among cattle for thousands of years, before jumping to humans once settlements began to surge in size in the late first millennium BCE. In a related Perspective, Simon Ho and Sebastián Duchêne discuss the study's results in more detail.
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Science