Measles, the most infectious of all humanity's afflictions, could have emerged 2,600 years ago, rather than 1,100 as previously thought, a new study reveals. In a bitter irony, measles diverged from the cattle disease rinderpest, since eliminated through vaccinations, but insufficient funding and the efforts of those against vaccinations mean measles is still killing hundreds of thousands of people.
There are no definitive accounts of people suffering measles in ancient times, but according to Dr Ariane Düx of the Robert Koch Institute, many plagues' symptoms leave historians uncertain as to their cause, with measles a possibility.
“Measles differential diagnosis remained a challenge well into more recent times, "Düx and co-authors write in Science.
Studies of existing measles strains suggest they diverged in the 9th century, so this has been treated as the time when the rinderpest virus leaped from cattle to humans and started its deadly dance. However, the paper points out that many measles strains have died out since the vaccine prevented their spread. An analysis of virus diversity at its peak, therefore, might yield an earlier date.
This is indeed what Düx found, having sequenced the genomes of two measles samples collected by the Czech National Reference Laboratory in 1960. Single-stranded RNA viruses usually degrade rapidly. However, Düx and co-authors managed to sequence the RNA of measles collected from the tissue of someone who died of measles in 1912 and whose lungs were preserved in the Berlin Museum of Natural History.
By comparing these samples and those from still-circulating measles viruses, the authors discovered measles diverged from rinderpest around 2,500 years ago. This does not necessarily mean the disease has been circulating in humans for all that time. An ancestor of measles may have initially infected cattle as well, or some other species entirely, and only crossed to humans later.
Nevertheless, the authors note that for most of human history cities were small enough that measles would have struggled to maintain itself, likely burning out rather than spreading widely. The point where the largest connected communities reached the size at which measles can maintain its grip was 2,000-3,000 years ago, a match that seems unlikely to be coincidental.
Professor Simon Ho of the University of Sydney published an accompanying comment about the capacity of ancient samples to inform us of when the disease emerged. Ho told IFLScience that tracing the origins of diseases does not necessarily help us fight that particular virus or bacteria.
However, “I think it is generally useful because it can tell us about the conditions in which diseases jump to humans and in which they can survive in humans.”
Ho noted that HIV, recently dated to pre-1920, is a priority for this sort of research, along with the quest to identify when and how SARS-CoV-2 made the jump to humans.