More than one-third of the individuals buried in an early medieval cemetery in Germany suffered from infectious diseases, a new study reveals.
Researchers from Kiel University in Germany examined the DNA and skeletal remains of 70 people who were buried in the community cemetery located in Lauchheim Mittelhofen, a town in what is now present-day Germany. All of the burials took place sometime during the Merovingian period (between the fifth and eighth centuries A.D.). The team discovered that more than 30% of the deceased had either hepatitis B; parvovirus B19 (which can lead to a rash); variola virus (the virus that causes smallpox); or Mycobacterium leprae (one of the two bacteria that causes leprosy). Seven of the infected individuals had a combination of two of the illnesses.
Using DNA extracted from the roots of each individual's teeth, the researchers determined what illnesses each person had, if any. They also examined the bones of the deceased, although "only some diseases leave clear traces on the bones," Ben Krause-Kyora, one of the study's co-authors and a biochemist and archaeologist at Kiel University, told Live Science in an email.
"The roots of the teeth are well supplied with blood during their lifetime, so the pathogens we find in them probably circulated in the bloodstream," Krause-Kyora said. "It takes a certain amount of time for bone to remodel in response to an infection. This is the case, for example, with leprosy, a relatively slow-progressing disease."
In terms of hepatitis B, which showed up in DNA rather than the skeletal remains, the illness "tends to lead to liver inflammation and, in rare cases, to liver failure or liver cancer," Krause-Kyora said. "Parvovirus and also smallpox don't leave any traces. In the case of the variant of this ancient smallpox, it's also unclear how exactly it worked, as it's already genetically different from the typical smallpox of modern times."
He added, "We wanted to show which pathogens circulated in an early medieval population and how high the infection rates were."
One skeleton in particular stood out amongst the burials: a young male who suffered from three pathogens, which included hepatitis B, parvovirus B19 and M. leprae.
"[The boy] is also special because leprosy was not yet widespread north of the Alps in the 7th and 8th centuries," Krause-Kyora said, "so we can also learn something about the origin of this later pandemic from the genome of the leprosy pathogen M. leprae" and how it evolved over the coming centuries.
So, why were so many people in this small, rural community afflicted by such a variety of illnesses? Researchers concluded that a number of factors could've been at play, such as climate change during the Late Antique Little Ice Age (the sixth and seventh centuries A.D.), which led to widespread crop failures and famine, Krause-Kyora said.
"Through climate reconstructions, we know of a general climate deterioration" during this time period, Krause-Kyora said, adding that temperatures in the Northern Hemisphere cooled by about 3.6 degrees Fahrenheit (2 degrees Celsius) on average.
"This phase of bad climate could also have led to a general weakening of the population through crop failure," he said. "This increased susceptibility to disease could've made it possible for diseases to jump from animals to humans and adapt to them as new hosts. In addition, the diseases can also spread more widely in new populations. This could be a plausible explanation of how pathogens became established in human populations and then led to large pandemic outbreaks after several centuries in the Middle Ages."
The findings were published Dec. 12 in the journal Genome Biology.
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Jennifer Nalewicki is a Salt Lake City-based journalist whose work has been featured in The New York Times, Smithsonian Magazine, Scientific American, Popular Mechanics and more. She covers several science topics from planet Earth to paleontology and archaeology to health and culture. Prior to freelancing, Jennifer held an Editor role at Time Inc. Jennifer has a bachelor's degree in Journalism from The University of Texas at Austin.