Scientists have discovered the oldest strain of Yersinia pestis – the bacteria that caused the Black Death, a devastating bubonic plague pandemic in the 14th century.
Y. pestis was found in the remains of a 5,000-year-old male, called RV 2039, in an area called Rinnukalns in present-day Latvia.
Genetic analysis reveals that this ancient strain was likely less contagious and not as deadly as the medieval version during the Black Death.
This early form of the plague that killed the RV virus 2039, around 3000 BC, was likely a slow-moving disease that was not highly transmissible.
However, over the next 4,300 years, the breed evolved to become more lethal to humans, culminating in the catastrophic Black Death in Europe and Africa.
Although the Black Death – which lasted from 1346 to 1353 – could have killed up to half of Europe’s population.
This image shows the skull bones of RV 2039, a man buried in Renokalnes, Latvia, about 5,000 years ago.
In the photo, a picture of plague victims as they were buried during the Black Death. The devastating bubonic plague ravaged Europe from 1346 to 1353
Plague is an infectious disease caused by the bacterium Yersinia pestis, which is carried by fleas and is transmitted between animals.
Bubonic plague – the most common form – is caused by the bite of an infected flea and can spread through contact with infectious body fluids or contaminated materials.
Patients may show signs of fever and nausea and at an advanced stage may develop open sores filled with pus.
It devastated medieval Europe, most notably in the Black Death in the 1440s which killed a third or more of the continent’s population.
After the Black Death epidemic became a common phenomenon in Europe, with regular outbreaks until the 18th century.
When the Great Plague struck in 1665, a fifth of the people died in London, the victims were locked in their homes and a red cross was painted on the door.
The bubonic plague has almost completely disappeared from the rich world. 90 percent of all cases are now in Africa.
It can now be treated with antibiotics, as long as it is taken quickly.
However, there have been few nonfatal cases in the United States, where an average of seven cases are reported annually, according to chiefs of disease control.
From 2010 to 2015, 3,248 cases were reported worldwide, including 584 deaths, says the World Health Organization.
The genetic analysis of RV 2039 was led by Ben Krause-Kyora, a biochemist and archaeologist at Kiel University in Germany.
“The most surprising thing is that we can delay the emergence of Y. pestis 2,000 years further than previously published studies suggested,” he said.
“It looks like we’re really close to the origin of the bacteria.”
RV 2039, who was between 20 and 30 years old at the time of death, was in fact one of two people whose skeleton was excavated in the late 19th century at Rinnukalns.
Soon after their remains were found, they both disappeared until 2011, when they reappeared as part of the German anthropologist Rudolf Virchow’s group.
After this rediscovery, other burials from the site were uncovered giving a total of four specimens, most likely from the same group of hunter-gatherers.
Krause-Kyora and his team used samples from the four’s teeth and bones to sequence their genomes and then tested them for bacterial and viral pathogens.
They were surprised to find evidence of Y. pestis in RV 2039, but not the other three samples.
After reconstructing the bacteria’s genome and comparing it to other ancient strains, the team realized that the Y. pestis strain carried by RV 2039 was the oldest strain ever discovered.
It is likely part of a lineage that emerged about 7,000 years ago, just a few hundred years after Y. pestis separated from its predecessor, Yersinia pseudotuberculosis.
“Surprisingly, we already see in this early strain the complete genetic set of Y. pestis, and there are only a few genes,” Krause-Kiura said.
“But even a small shift in genetic settings can have a huge impact on virulence.”
Y. pestis can infect humans via the oriental rat flea (Xenopsylla cheopis), which is carried by rodents – as the name implies.
However, this newly discovered ancient strain lacks one crucial component – the gene that first allowed fleas to act as vectors to spread the plague.
This gene was responsible for the efficient transmission of the bacterium to human hosts, resulting in the growth of pus-filled neutrophils in patients associated with the Black Death.
Jawbone RV 2039. The man was between 20 and 30 years old at the time of death, researchers estimate
The plague hunter-gatherer was one of two people whose skeleton was excavated in the late 19th century in an area called Rinokalnis in present-day Latvia
Flea-dependent transmission also requires the death of the human host, which means that the appearance of the gene could have led to the development of a more deadly disease.
Starting with RV 2039, it will likely take more than 1,000 years for Y. pestis to acquire all the mutations needed for flea-based transmission.
But it’s not clear to what extent RV 2039 suffered from the worst effects of the plague — boils, hemorrhages, and weakness, to name a few.
Although Y. pestis was found in the bloodstream, which means that it most likely died of a bacterial infection, the course of the disease may have been rather slow.
The researchers noted that he had a high number of Y. pestis bacteria in his bloodstream when he died. But in earlier studies in rodents, a higher bacterial load of Y. pestis was associated with less aggressive infections.
Rinnukalns, a Stone Age shell moored on the banks of the Salaca River near the outflow from Lake Burtniek
In addition, the people who were buried near them were not infected, which reduces the likelihood of contracting a highly contagious respiratory version of the plague.
The 5,000-year-old strain was likely transmitted directly by a bite from an infected rodent and may not have spread after RV 2039.
Some historians have suggested that infectious diseases such as Y.pestis mostly developed in cities of more than 10,000 people near the Black Sea.
However, 5,000 years ago – the era of the RV dynasty 2039 – was long before the formation of large cities, which puts these theories into question.
Instead, agriculture was just beginning to emerge in central Europe, and the population was much smaller.
3D illustration of Yersinia pestis – the bacteria behind the Black Death in the 14th century
This new study also contradicts the idea that Y. pestis led to a significant population decline in Western Europe in the late Neolithic period (3000 to 2500 BC).
The authors say that examining the history of Y.pestis could also shed light on the history of the human genome.
“Different pathogens and the human genome have always co-evolved,” Krause-Kura said.
We know that Y. pestis bacteria likely killed half of Europe’s population in a short time frame, so it must have had a significant impact on the human genome.
“But even before that, we see a huge change in our immune genes at the end of the Neolithic, and we could see a huge change in the nature of pathogens at that time as well.”
The study was published in the journal Cell Reports.
The bubonic plague: the third of Europe was wiped out in the fourteenth century
The bubonic plague is one of the deadliest diseases in history, killing about 100 million people during the “Black Death” of the 14th century.
Drawings and paintings from the outbreak, which wiped out about a third of Europe’s population, depict city cries saying “Bring out your dead” while towing trailers piled with infected corpses.
It is caused by a bacterium known as Yersinia pestis, which uses fleas as a host and is usually transmitted to humans by mice.
The disease causes horrific symptoms such as gangrene and the appearance of large bulges on the groin, armpit or neck known as “bubo”.
It kills up to two-thirds of infected people within just four days if not treated, although if antibiotics are given within 24 hours of infection, patients are more likely to survive.
After the arrival of the Black Death in 1347, the plague became a common phenomenon in Europe, with regular outbreaks repeating until the 18th century.
The bubonic plague has almost completely disappeared from the rich world, with 90 percent of all cases now found in Africa.
However, there have been a few nonfatal cases in the United States in recent years, while a 15-year-old boy died in Kyrgyzstan in August 2013 after eating a groundhog infected with the disease.
Three months later, an outbreak in Madagascar killed at least 20 people in a week.
A year before the disease, 60 people died as a result of the infection, more than any other country in the world.
Outbreaks in China have been rare in recent years, and have mostly occurred in remote rural areas of the West.
China’s state broadcaster said there were 12 diagnosed cases and three deaths in Qinghai Province in 2009 and one in Sichuan in 2012.
In the United States between five and 15 people die each year as a result, most of them in western states.