Paleogeneticists have studied the DNA of 46 people whose remains were excavated from several ancient burial grounds located in the Baikal region. Scientists have discovered that more than five thousand years ago, local hunter-gatherers suffered from outbreaks of plague, and at that time, apparently, this disease posed the greatest threat to children and adolescents. This is reported in a preprint posted on the website bioRxiv.org.
Genetic studies in recent years have shown that people suffered from the plague long before the first known pandemics recorded in written sources. Thus, scientists have already discovered a number of cases when ancient people contracted this infection more than five thousand years ago. For example, the DNA of the plague bacillus was isolated from the remains of people who lived about 5,700–5,300 years ago in the west of modern Russia, in Central Asia and in the Baikal region.
In addition, in recent works, paleogeneticists have described a number of cases of plague infection in ancient inhabitants of the Baltics and Scandinavia. For example, a couple of years ago, scientists discovered DNA of the plague bacillus in the remains of a hunter-gatherer who died in the territory of modern Latvia about 5,300–5,050 years ago. More recently, researchers have identified cases comparable in age in Germany and Scandinavia, and in the latter they found signs that the plague already had epidemic potential.
Scientists from the UK, Denmark, Canada, Russia and the US, led by renowned paleogeneticist Eske Willerslev, have returned to studying the remains of ancient hunter-gatherers who lived in Siberia. They sequenced DNA from the bones and teeth of 46 Neolithic people whose burials were excavated in four burial grounds in the Baikal region (Angara): Shumilikha (5,580–5,320 years ago), Ust-Ida-I (5,600–5,320 years ago), Bratsky Kamen (5,475–5,052 years ago) and Serovo (5,290–4,870 years ago).
The researchers first noted that they had found fairly long common ancestry linkage blocks in the genomes of hunter-gatherers buried approximately 340 kilometers apart. This suggests that the people were related and that the ancient population of the Angara region was quite mobile. The scientists also found that the genomes of these people lacked long regions of homozygosity, indicating that they avoided inbreeding. Based on this indicator, the researchers estimated the effective population size of local hunter-gatherers at approximately 18,219 people (9,445–42,062 people at a 95 percent confidence interval).
Scientists have discovered that one of the people buried in the Ust-Ida-I burial ground suffered from brucellosis. In another 18 cases, they found plague bacillus DNA in the remains of people. Most of the samples came from the Ust-Ida-I site, where the pathogen's genetic material was found in 12 of the 31 skeletons studied. One case each was found in the Shumilikha and Serovo burial grounds, and the remaining four were found in the Bratsky Kamen burial ground.
A detailed analysis of the remains from the aforementioned sites showed that the plague bacillus was probably already causing outbreaks of the disease. Moreover, the disease probably posed the greatest threat to children and adolescents. Thus, a study of the materials from the Ust-Ida-I and Bratsky Kamen burial grounds showed that the peak mortality rate was among children aged 7.5–11 years. Moreover, the burial grounds contained burials containing the remains of children who were probably related. For example, at the Bratsky Kamen site, archaeologists excavated a triple burial of four- to nine-year-old girls infected with the plague bacillus, two of whom were third-degree relatives (probably cousins), and the third was possibly related to them on the maternal side (the preservation of her DNA was poor, so we cannot say for sure).
Among other things, the researchers also revised the time of the divergence of the bacteria Yersinia pestis and Y. pseudotuberculosis. According to new estimates, their evolutionary lines diverged about 9,317 years ago (7,289–11,344 at a 95 percent confidence interval), that is, earlier than previously thought.
Paleogeneticists have found plague bacilli not only in the remains of ancient people. For example, scientists recently isolated the DNA of this pathogen in the bones of a dog that lived on the island of Gotland about 4,900–4,500 years ago.
