What Really Caused the Black Death: Anthrax or Celestial Bodies?

FROM THE LECTURE SERIES: The Black Death: The World's Most Devastating Plague

By Dorsey Armstrong, Ph.D., Purdue University

For centuries a bubonic plague epidemic was considered to be the prime cause of the Black Death. Based on inconsistencies and divergences on the cause of what ultimately killed half of Western Europe’s population, scientists started reexamining the evidence with renewed interest in modern times and came up with new theories.

The painting of a cart with the dead.
The Black Death killed half the population of Western Europe. (Image: Wellcome Images/CC BY SA/4.0/Public domain)

A Radical Revision

In 1984, an epidemiologist named Graham Twigg published what at the time was considered a radical rethinking of the causes of the Black Death. He argued that most deaths in the medieval epidemics were not caused by the plague at all but, in fact, were due to exposure to anthrax.

Anthrax is a bacillus—like Yersinia Pestis— and it is found to be naturally occurring on every continent, including Antarctica. Infection usually occurs when grazing animals inhale the Bacillus anthracis spores. If we consume meat from infected animals, the infection transfers to humans.

Humans can also contract anthrax if they directly come in contact with it in nature. Anthrax spores are extremely long-lasting and hardy. They have been discovered in soil covering an animal that died of Anthrax infection 70 years after the fact.

This is a transcript from the video series The Black Death: The World’s Most Devastating Plague. Watch it now, on The Great Courses Plus.

Anthrax as the Cause of the Outbreak

If a person inhales anthrax spores, they usually have some flu-like symptoms for a few days, then experience severe pneumonia and respiratory collapse—all familiar symptoms of the pneumonic form of plague.

Also, if a piece of infected meat is consumed, the individual will experience serious GI issues and end up vomiting blood, again symptoms associated with all three forms of plague. And, even more to the point, boils and lesions often show up on the bodies of those infected with anthrax.

Image of anthrax in a petri dish.
Historically, it’s estimated that fatality rates for anthrax were around 85 percent. (Image: Jose L Vilchez/Shutterstock)

Historically, it’s estimated that fatality rates for anthrax were around 85 percent. In modern times, if anthrax is diagnosed and treated quickly, the fatality rate is closer to 45 percent.

Considering that this pathogen can survive even decades after the death of its host as well as the lack of proper burial for diseased animals in the Middle Ages, the theory of anthrax as the underlying cause of the Black Death appears logical. This hypothesis can also explain why the plague would flare up every decade or so after its initial wave swept through the medieval world.

Learn more about later plague outbreaks: 1353-1666.

Murrain Contribution

Historian Norman Cantor points out that anthrax spores have been found in a mass grave, dating from the Middle Ages in Scotland. There’s evidence that meat from slaughtered murrain-infected cattle was sold in villages in England shortly before the first big outbreak there in 1348.

There are some scholars who have found much that is persuasive about this theory. But they have more cautiously proposed that while anthrax may be the cause, it would be safer and more accurate to argue that some sort of cattle and/or sheep murrain may have been a contributor.

Murrain, originally and appropriately, is a medieval word that at first just meant death, but it gradually underwent linguistic specialization and came to mean any disease that affected cattle and sheep.

Death from Outer Space

There are other interesting and even terrifying theories about the origin of the plague.

One theory argues that the Black Death originated from outer space. This theory was first proposed in 1979 by Fred Hoyle, a Cambridge University astrophysicist, and Nalin Chandra Wickramasinghe in their co-authored book, Diseases from Space.

They believe that Darwin’s theory of evolution is correct up to a point, but the elements indigenous to Earth are not enough to contribute to the development of flora and fauna on our planet. For life to flourish on Earth, some external or exogenous elements were essential.

Based on the panspermia hypothesis, the seeds of life exist all throughout the universe, and those seeds move through the galaxies as parts of comets, asteroids, and other celestial objects. Some of them carry pathogens, and when they crash into a planet like Earth, we have what Hoyle and Wickramasinghe call vertical transmission.

The Horizontal Transmission of a Disease

Graphic image of a meteor shower.
Hoyle and Wickramasinghe argue that the bubonic plague may have been vertically transmitted from space. (Image: Vadim Sadovski/Shutterstock)

Once that disease establishes a foothold on Earth and finds some reservoirs or hosts it can hang out in, then horizontal transmission—from animal to animal or person to person or animal to person—can occur.

They argue that the bubonic plague appears to be a likely candidate for a disease that was vertically transmitted from space. They claim that this explains why the plague appeared in the 6th century, then again in the 14th, and once more in the 19th, with substantial gaps in between the outbreaks.

Learn more about the economics of the Black Death.

Rats or Comets?

This explains how Yersinia Pestis was introduced on our planet. Just as planetary objects like the Halley’s Comet pass by Earth in regular intervals, there is a possibility that unnoticed comet-like objects, rained down the plague bacteria and found its most willing hosts in black rats.

Indeed, while the authors acknowledge the role that the black rat played in the outbreak of the Black Death, they also are quick to point out the flaws in the theory that these rodents were the main vehicle of transmission:

What remarkable rats they were, to have crossed the sea and to have marched into remote English villages, and yet to have effectively bypassed the cities of Milan, Liège and Nuremberg. There was no marching army of plague-stricken rats. The rats died in the places where they originally were.

The idea that life on Earth—at least some of it—may have originated elsewhere has some scientific merit. After all, there is substantial meteoric traffic among the inner planets, and there are plenty of microbes that could survive the journey through space.

However simultaneously, the specifics of Hoyle and Wickramasinghe’s theory is considered very fringe by the scientific community at large, and pretty much every mainstream scientist is of the view that the theory doesn’t really hold water and certainly can’t be proved.

Common Questions about the Causes of the Black Death

Q: According to epidemiologist Graham Twigg what was the cause of the Black Death?

Graham Twigg argued that the Black Death in the medieval times was not caused by the plague at all but, in fact, was due to exposure to anthrax.

Q: Why deaths caused by anthrax can be misdiagnosed as plague-induced?

If a person inhales anthrax spores, they usually have flu-like symptoms for a few days, then experience severe pneumonia and respiratory collapse—all familiar symptoms of the pneumonic form of plague. Moreover, if a piece of infected meat is consumed, the individual will experience serious GI issues and end up vomiting blood, again symptoms associated with all three forms of the plague.

Q: Based on the idea of vertical transmission, how was Yersinia Pestis introduced on Earth?

Just as planetary objects like the Halley’s Comet pass by Earth in regular intervals, there is a possibility that unnoticed comet-like objects, rained down the plague bacteria and found its most willing hosts in black rats. This is how Yersinia Pestis was introduced on earth.

Keep Reading
The Three Forms of Plague: Bubonic, Pneumonic, and Septicemic
The Medieval European Society in the Early 14th Century
The Black Death: Symptoms and Diagnosis of The Plague