Angela Lieverse
The skull of a girl around 10 years old, discovered at the Ust-Ida cemetery in southeastern Siberia, Russia.
The word plague typically conjures up terrifying images of the Black Death, the pandemic that killed more than a third of the European population during the 14th century. However, the bacteria responsible for the disease is much older than previously thought.
A team of scientists discovered that the plague has existed for at least 5500 years.
In a new one, published this Wednesday in Natureresearchers recovered and sequenced ancient DNA extracted from the teeth of 42 prehistoric hunter-gatherersincluding several children and teenagers, from four archaeological sites located nearby the Lake Baikalin Siberia.
The genetic material analyzed contained DNA from the individuals themselves and also from the bacteria responsible for the plague, the Yersinia pestisidentified in 18 of the skeletons studied.
According to , this work constitutes the oldest evidence known number of plague outbreaks and provides the first test that the first genetically distinct strains of Yersinia pestis were capable of causing deadly diseases in humans.
Until now, the oldest strains of Y. pestis identified had wax. 5300 years and may not have been virulent enough to cause serious illness.
DNA analysis points to two distinct outbreaks of plague in the same region of southeastern Siberia. One occurred approximately 5,500 years ago and another a few centuries later. During the first outbreak, several close relatives died in a short space of time at one of the sites studied, called Ust’Ida, and were buried in mass graves.
“The most plausible explanation for this mass mortality is a widespread plague infection. Furthermore, we discovered that the same strain infected other people, at the same time, in another place located 37 kilometers away“, stated the first author of the study, Roderick Macleod.
The team also identified kinship ties between victims associated with both outbreaks and buried in different graves. According to Macleod, this evidence suggests that the same populations were exposed, over several hundred years, to new outbreaks of plague from the same species of wild rodent that was the disease’s host.
A significant number of children also died from the plague in Ust’Ida and in another place called Bratskii Kamen. Infant mortality was particularly high in Ust’Ida during the first outbreak and in Bratskii Kamen during the second. In general, the most serious manifestations of the disease seem to have affected mainly children with ages between eight and 11 years old.
According to researchers, the strain of Y. pestis responsible for both outbreaks was until now unknown and may have emerged approximately 5700 years. Furthermore, it had a gene that was absent from modern and historical strains of the bacteria, which may have increased the severity of the infection, especially among children.
The study challenges some previously accepted ideas about the spread of diseases in Prehistory. One of them argued that outbreaks capable of affecting entire communities only emerged after the transition from hunter-gatherer groups to the first agricultural societies.
This transformation, called neolithic transitionallowed the emergence of more numerous communities and, later, the first cities. The new discoveries demonstrate, however, that the plague already caused devastating impacts in small mobile groups of hunter-gatherers before this change.
The results also contradict the theory that prehistoric strains of the plague would have been less deadly because they lacked certain genes associated with the Black Death and flea transmission. The strain now identified demonstrates that variants of the bacteria could still be extremely dangerous.
