This is what causes the plague. <em>Yersinia pestis</em> bacteria, colored in yellow, are seen on the spines inside a flea's digestive system.
This is what causes the plague. Yersinia pestis bacteria, colored in yellow, are seen on the spines inside a flea's digestive system.
National Institute of Allergy and Infectious Diseases
The bacterium that is responsible for the plague can sometimes infect the blood, causing the hands, feet, nose and lips to become gangrenous and black. This form of the disease is almost always fatal if not treated with antibiotics.
The bacterium that is responsible for the plague can sometimes infect the blood, causing the hands, feet, nose and lips to become gangrenous and black. This form of the disease is almost always fatal if not treated with antibiotics.
CDC / Dr. Jack Poland
A map shows reported cases of human plague in the United States from 1970 to 2012. Nearly all cases occur in the western U.S., for reasons that are not entirely understood. Plague first came to the U.S. in 1900 via rats on steamships from Asia.
A map shows reported cases of human plague in the United States from 1970 to 2012. Nearly all cases occur in the western U.S., for reasons that are not entirely understood. Plague first came to the U.S. in 1900 via rats on steamships from Asia.
CDC
Rats are one of the many rodent species that carry the plague. The disease is typically spread to people through a bite from a rodent flea. Although recent research may exonerate rats as primarily responsible for the Black Death, and instead put the blame on gerbils, rats probably played a role in that and other plague epidemics.
Rats are one of the many rodent species that carry the plague. The disease is typically spread to people through a bite from a rodent flea. Although recent research may exonerate rats as primarily responsible for the Black Death, and instead put the blame on gerbils, rats probably played a role in that and other plague epidemics.
Time Life Pictures/Getty Images
The plague doctor is in. The hat, goggles, gown and beak-like mask identified a person as a plague doctor in the Middle Ages. The uniform was used for protection; the beak contained herbs and perfumes intended to cover the stench associated with plague disease.
The plague doctor is in. The hat, goggles, gown and beak-like mask identified a person as a plague doctor in the Middle Ages. The uniform was used for protection; the beak contained herbs and perfumes intended to cover the stench associated with plague disease.
A patient with plague symptoms, foreground, awaits test results with his mother at New Delhi's Disease Hospital in 1994. Pneumonic plague, which infects the lungs, is the most serious form of the disease and the only way it can spread directly between people. A plague outbreak in India in 1994 was among the most serious in the world in recent decades.
A patient with plague symptoms, foreground, awaits test results with his mother at New Delhi's Disease Hospital in 1994. Pneumonic plague, which infects the lungs, is the most serious form of the disease and the only way it can spread directly between people. A plague outbreak in India in 1994 was among the most serious in the world in recent decades.
AP Photo/John Moore
Taylor Gaes died of the plague this spring, a day before he would have turned 16. Officials think he was infected from a flea bite on his family's ranch in Larimer County, Colorado. The high school sophomore began having flu-like symptoms after he pitched in a baseball game. Although plague remains rare, it is often mistaken for the flu because it causes fever and chills.
Taylor Gaes died of the plague this spring, a day before he would have turned 16. Officials think he was infected from a flea bite on his family's ranch in Larimer County, Colorado. The high school sophomore began having flu-like symptoms after he pitched in a baseball game. Although plague remains rare, it is often mistaken for the flu because it causes fever and chills.
From Poudre High School
Plague: a scourge of biblical proportions

Story highlights

Scientists sequence the genome of the pathogen responsible for sixth-century plague

The new genome was reconstructed using human skeletal remains

It offers "a better understanding of the history and the biology of the disease," expert says

CNN  — 

Scientists have just reconstructed the genome of an ancient plague, which may shed new light on how certain diseases can either mysteriously disappear or continue to evolve and spread.

About 1,500 years ago, frequent outbreaks of the world’s first known plague, caused by the bacterium Yersinia pestis, killed more than 25 million people and sickened many others in the Mediterranean basin with “flu-like” symptoms. The pandemic, which was called the Justinian Plague after the sixth-century Byzantine emperor Justinian I, lasted to the mid-eighth century.

Now, researchers in Germany have sequenced the genome of the Y. pestis strain that they believe caused the Justinian Plague but hasn’t been seen since, according to a new study published in the journal Molecular Biology and Evolution on Tuesday.

plague explainer cohen orig mg_00001604.jpg
plague explainer cohen orig mg_00001604.jpg
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Variations of Y. pestis are thought to have caused at least three known plague pandemics. The Justinian plague was the first, and the Black Death, a pandemic that emerged in the Middle Ages and killed up to half of the European population, was the second. The third plague pandemic began in late 19th-century China, giving rise to many of the subsequent plagues that exist today.

The newly sequenced genome reveals that the Y. pestis strain linked to the Justinian Plague indeed differs from the strain linked to the Black Death. (A genome of the Y. pestis strain behind the Black Death was published in a separate study in 2011.)

Therefore, “this study provides a better understanding of the history and the biology of the disease,” said Michal Feldman, a researcher at the Max Planck Institute and the University of Tubingen in Germany, who served as first author of the study.

“We still do not know why the Justinian plague suddenly vanished,” Feldman said. “The bacterium causing the Black Death and the Justinianic one is the same bacterium, Y. pestis, and this was already reported on in previous studies. However, the strains of the bacteria – you can also call them variations if you like – causing the two pandemics were different, and the Justinianic strain is extinct today.”

Old bones hold new clues

The researchers examined the skeletons of two Justinian plague victims. The remains were unearthed in 1966 among several hundred other skeletons in a large medieval cemetery in rural southern Germany.

“A communal burial indicates simultaneous death, or death close in time of those interred, and could therefore also indicate that an epidemic occurred,” said Andreas Rott, a researcher at the State Collection of Anthropology and Palaeoanatomy in Munich, Germany, and a co-author of the study.

An adult woman's skeleton, left, and adult man's skeleton tested positive for the presence of Y. pestis. A third molar was sampled from the woman (see arrow) to sequence the bacterium's genome.
An adult woman's skeleton, left, and adult man's skeleton tested positive for the presence of Y. pestis. A third molar was sampled from the woman (see arrow) to sequence the bacterium's genome.
State Collection of Anthropology and Palaeoanatomy Munich

The teeth of the plague victims, a man and a woman, were analyzed and used to extract DNA samples. The researchers separated the human DNA from bacterial DNA in order to sequence the Y. pestis genome.

After analyzing the reconstructed genome, the researchers found clues that this ancient strain of Y. pestis might have had Chinese origins, which was also found in a 2014 study from a separate research team.

Plague carriers can spread disease still, scientists created a predictive map to use as a tool to fight the disease.
Plague carriers can spread disease still, scientists created a predictive map to use as a tool to fight the disease.
Shutterstock

Related article Scientists create new tool to fight spread of the plague

Additionally, the new findings provide evidence that the Justinian plague hit rural Germany. “But more data is needed to determine the rate in which the disease had spread,” Feldman said.

“How the pathogen reached southern Germany is at present unknown. Possibly, it traveled across the Alps from the Mediterranean or from France and western Germany. It could have also traveled up the Danube [River] from the east,” Feldman said. “The exact trade routes that the disease traveled in are a subject of debate among scholars. It was transmitted either by people or by rats that were ‘traveling’ with cargo.”

‘Always good to have more ancient genomes’

Between 1,000 and 2,000 plague cases caused by Y. pestis are reported to the World Health Organization each year, according to the Centers for Disease Control and Prevention. The three most endemic countries are Madagascar, the Democratic Republic of Congo and Peru.

In the United States, 15 people were infected with the bubonic plague last year, and about four of them died.

Antibiotics and antimicrobials are often used to treat the plague. However, with further research, many scientists think that the genomes of ancient pathogens could lead to improved treatments to eliminate plague-related deaths.

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    “I think it’s interesting and always good to have more ancient genomes,” said Hendrik Poinar, a molecular evolutionary geneticist and biological anthropologist at McMaster University in Canada, who was not involved in the new study.

    More genomes could allow scientists to better detect any small changes in the evolution of a pathogen that may affect how quickly it can spread and cause disease, Poinar said. “Those sorts of things are critical for understanding eradication in currently plague-hit areas, such as Madagascar.”