Dermatologic Manifestations of Pulmonary Disease

Ancestor Of Black Death Has Been Discovered In Bronze-Age Sheep

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An ancestor of the bacteria responsible for plague has been found in the tooth of a sheep that lived nearly 4,000 years ago in a Bronze Age human settlement, scientists report in a new preprint study.

Millennia later, the apparent descendants of this pathogen would unleash vicious pandemics that claimed millions of human lives, including the 6th-century Justinian plague and the 14th-century Black Death.

In tracing the backstories of diseases like plague, this new research highlights the importance of looking not just at ancient human remains, but also the animals around them, the authors say.

Most human pathogens have zoonotic origins, and many likely arose in prehistoric pastoral settlements, where crowds of humans and livestock created many novel spillover opportunities.

The bacteria behind the plague, Yersinia pestis, has been intensively studied using ancient DNA, with almost 200 genomes reconstructed from traces found in human remains.

Yet we know much less about ancient plague in other species, with just one partial genome recovered from a medieval rat.

All modern strains of plague bacteria can be traced back to a common ancestor in Eurasia during the Late Neolithic and early Bronze Age, roughly 3,800 years ago, as previous research suggests.

Pastoralism was fairly new back then, as humans were only a few millennia into the shift from foraging to producing food in year-round settlements.

Those settlements were increasingly abuzz with domesticated mammals, whose population density and proximity to people raised the risk of trouble.

"In particular, the domestication of sheep, goats, pigs, and cattle and their cohabitation with people have been hypothesized as drivers for the emergence of deadly human pathogens causing infectious diseases as varied as tuberculosis, salmonellosis, measles, and plague," the researchers write.

One site that fits the profile of a springboard for early plague is Arkaim, a fortified Bronze Age settlement in the Southern Ural Mountains.

Back then, an earlier form of Y. Pestis caused periodic outbreaks among humans in Eurasia, but without key genetic features of flea transmission, suggesting this plague spread without fleas.

Known as the Late Neolithic Bronze Age (LNBA) lineage, this form has been identified from dozens of human archaeological remains across Eurasia, but not from any other species.

It's now presumed extinct, but research suggests LNBA plague endured for two millennia, from about 2900 to 500 BCE, at a time of "heightened pastoralist mobility and interaction throughout the Eurasian steppes," the authors write.

The advent of horse riding, the authors propose, led to a pastoralism boom in Centra Asia's Sintashta culture 4,000 years ago.

Large, dense livestock herds were more likely to contract LNBA plague from natural reservoirs like wild rodents or birds, the authors suggest, and to enable a leap to people – even without fleas.

There is scant evidence of cultivated crops at Sintashta settlements, the authors point out, suggesting they lacked the kind of grain stores that drew flea-ridden rats into humans' midst in later plague pandemics.

Unable to transmit efficiently via fleas, LNBA plague may have spread to humans via sheep and other livestock.

"It was remarkable to discover a domesticated sheep from the Bronze Age that was infected with LNBA plague. This gave us an important clue for how plague could transmit within pastoralist communities without fleas as vectors," says University of Arkansas anthropologist Taylor Hermes.

This is the first time LNBA plague has been found in a nonhuman animal, and the researchers were able to recover the pathogen's genome – a rare feat, they note, since livestock remains tend to be jumbled, dispersed, and degraded.

These insights could help demystify the evolutionary history of plague bacteria, which remain a public health threat in some parts of the world.

"The identification of a Bronze Age Y. Pestis genome from a domesticated sheep offers a novel perspective on the hidden evolution and host range of a prehistoric pathogen," they write, "and sets a precedent for the exploration of ancient diseases beyond humans."

The study, which has not yet been peer-reviewed, is available as a preprint on bioRxiv.

Related News

The Bubonic Plague Still Exists — Here's How You Get It And How To Treat It

 The bubonic plague is a deadly bacterial infection, caused by Yersinia pestis. In the 14th century, before treatment was available, bubonic plague killed 50 million people in Europe and became known as the "Black Death." 

But in modern times, bubonic plague is rare affecting between 1 and 17 people per year in the United States. 

Bubonic plague is still deadly if not treated, so it's important to seek medical aid immediately if you think you have it. Here's what you need to know about how to treat and prevent bubonic plague.

How do you get bubonic plague?

The bubonic plague has a frightening history, but there is little risk of it becoming a global threat, says Michael Head, PhD, a senior research fellow in Global Health at the University of Southampton. "There are a few hundred cases of plague globally each year, so the disease itself is relatively rare."

It is found mainly in Africa, Asia, and South America. Countries with the most number of cases are usually Democratic Republic of Congo, Peru, and Madagascar. There are also occasional plague cases in the western United States mostly in two areas: the Southwest four corners region and the Northwest in California and Oregon.

One reason bubonic plague is uncommon is that it is rarely transmitted between people. It's possible to pass it on through a cough, but the most common way to catch plague is through a bite from an infected flea or animal. 

How does the bubonic plague affect your body?

Bubonic plague targets your lymph nodes, which are located throughout your body. They are round clusters of immune cells that fight off invading microbes.

When plague bacteria enter your system, they multiply inside the closest lymph node. This can cause swollen, painful lymph nodes, most often found in your groin, neck, or armpit. If you aren't treated for bubonic plague, the infection can spread through your whole body.

In addition to swollen lymph nodes, other symptoms of bubonic plague include:

Fever that comes on suddenly

Chills

Headache

Weakness

Nausea and vomiting

If you catch bubonic plague, symptoms will take between one to seven days to show up after you are exposed. Symptoms will usually worsen rapidly, which is why it's important to seek treatment immediately.

Other forms of plague 

Depending on where the Y. Pestis bacteria spreads in your body, you can develop two additional forms of plague:

Pneumonic plague occurs when Y. Pestis spreads to your lungs. This condition is extremely dangerous and infected people can die within 18-24 hours of being exposed to the bacteria if they are not quickly treated with antibiotics.

Septicemic plague is caused by plague bacteria spreading through your bloodstream. This form of plague can cause other troubling symptoms — your skin and other tissue can turn black and die, particularly on your nose, fingers, and toes. You may also bleed out of your mouth, nose, or anus.

Treatment and prevention of the bubonic plague

To diagnose bubonic plague, your doctor will test your blood, mucus, or pus from swollen lymph nodes to look for the Y. Pestis bacteria.

If you test positive for bubonic plague, "immediate treatment is essential," Head says. 

"If untreated, bubonic plague has a mortality rate of around 50%," Head says. If you get treated with antibiotics, the death rate drops to about 11%.

Doctors will usually give antibiotics like streptomycin, gentamicin, doxycycline, or ciprofloxacin to treat bubonic plague. You may also need to get intravenous fluids and oxygen to help your body through the treatment process.

If you are traveling to a region with a higher plague risk, it may help to take precautions against flea bites. Wear long-sleeve shirts and pants to protect your skin and use a DEET-based bug spray to repel fleas. You should also stay away from any animals you suspect may have fleas.

The bottom line

Most people have a very low risk of getting bubonic plague. If you are visiting a country known to have above-average cases of bubonic plague, make sure you are aware of plague signs and symptoms. If you think you may have bubonic plague, get medical help immediately.

Ancient Ancestor Of The Plague Discovered In Bronze Age Sheep

Yersinia pestis bacteria viewed with an electron microscope

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An ancient ancestor of the pathogen that would later cause the Black Death and other major pandemics has been identified in a Bronze Age domestic sheep in Russia – making it one of the oldest pathogens ever found in an animal.

Its DNA closely matches that of plague bacteria found in European human skeletons from the same period, providing the first evidence that the disease could have spread between humans and their own livestock well before the pathogen evolved to jump from rodents to people via fleas.

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