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Could the Black Death Happen Again?

Dr. Thomas Swan has PhDs in physics and psychology and is an avid student of world history.

The Black Death killed about a third of the world's population in the 14th century.

The Black Death killed about a third of the world's population in the 14th century.

What Was The Black Death?

The Black Death was a bacterial infection that became a pandemic in the years 1346-1353. The disease is thought to have originated in black rats and found its way into humans via fleas that fed on both species.

The Black Death works by blocking a flea's gut (see picture). The starving insect then bites its host more aggressively while simultaneously trying to regurgitate the diseased blockage. An expulsion of bacteria into the bite wound infects the current human or animal host.

An Oriental rat flea with the Black Death infecting its gut (dark region).

An Oriental rat flea with the Black Death infecting its gut (dark region).

The Black Death most likely originated in the 1330s in the Kyrgyzstan area of central Asia before spreading to Europe. When an invading Mongol army catapulted its infected dead into a European settlement in 1347, fleas carrying the disease found their way onto rats and people aboard ships traveling in the Mediterranean Sea.

When the boats reached the over-populated, rat-infested cities of Europe, the fleas enjoyed regular contact with humans. However, recent research suggests that human-human contact quickly became the primary vector of transmission via infected body lice and fleas of the kind found on humans (i.e., not from rats).

The disease killed 75–200 million people, or about a third of the population of the world. Those suffering from the disease had their doors painted with a red or black cross to warn other people away.

The main Black Death symptoms are buboes (swollen lumps as big as apples), black blotches on the skin, fever, vomiting blood, and death in less than a week. An even deadlier pneumonic variant of the disease infects the lungs, producing flu-like symptoms that may have allowed for more efficient transmission between humans.

Yersinia Pestis (pictured) caused the bubonic plague and the black death.

Yersinia Pestis (pictured) caused the bubonic plague and the black death.

The Causes of the Black Death

To understand if the Black Death could return, it is worth investigating the bacterium responsible and the environmental factors that contributed to the original pandemic.

Many scientists now believe the Black Death was caused by Yersinia pestis. For those without a degree in epidemiology, this bacterium is famous for causing the bubonic plague: a disease that ravaged Europe in the 17th century.

Some researchers have questioned the plague connection, but the issue was put to rest when fragments of Yersinia pestis DNA were discovered in the graves of black death victims. Small discrepancies showed that the black death bacterium had evolved since the 14th century, suggesting the original disease no longer exists.

Black death victims showed evidence of having suffered from bubonic plague.

Black death victims showed evidence of having suffered from bubonic plague.

One of the main causes of the black death was a sustained cold climate. Europe went through a "Little Ice Age" from the 14th to 19th centuries (see below), causing poor harvests, widespread famine, and malnutrition.

The chilly weather weakened people's immune systems, which increased their susceptibility to disease. Studies have revealed that many of the dead suffered from malnutrition, suggesting that the Black Death was selective in picking off the vulnerable.

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Another factor was the unseasonably warm weather that preceded the Little Ice Age. Agricultural tools had been developed for softer soil, and an excess of food had convinced people to have large families. Thus, over-population and difficulty harvesting food in colder climates worsened the famine and created millions of vulnerable people.

Long-term cold temperatures typified the black death (1350) and plague (1665).

Long-term cold temperatures typified the black death (1350) and plague (1665).

Poor medieval sanitation also contributed to the pandemic. Filthy streets covered with livestock, rats, and excrement were common in European cities, and homes were often shoddy and open to pest invasion.

Consistent with contemporary accounts, it is likely that the effects of the Black Death were intensified by other illnesses such as pox, worms, typhus and dysentery.

Visible symptoms of the black death.

Visible symptoms of the black death.

Could the Black Death Return?

The black death never completely died out after the 1348-1351 pandemic. Sporadic recurrences continued until another major outbreak in 1664-1665. The disease then steadily declined in prevalence until a "Third Pandemic" began in China in 1855. This third wave struck India in 1896, killing more than 10 million people. Minor outbreaks also occurred in San Francisco from 1900-1904 and Australia from 1900-1925.

The Black Death is still being contracted by people today. Around 1000 to 3000 cases occur each year with a death rate of about 10%. Indeed, there were 10 reported cases in the United States in 1993, of which nine recovered with the aid of antibiotic drugs. The primary modes of infection were flea or animal bites.

Despite the success of modern antibiotics, the Yersinia Pestis bacterium may develop an immunity. Currently, there is no vaccine for the Black Death, and the prospect of another pandemic arose when a drug-resistant strain was found in Madagascar in 1995.

The Yersinia Pestis bacteria in a 16 year-old boy had developed resistance to eight forms of antibiotics. Researchers concluded that the resistant genes had been augmented from other forms of bacteria such as salmonella and E. coli.

The more we use and abuse antibiotics, the more likely it is that drug-resistant bacteria will transfer their resistances to lethal strains of Yersinia Pestis. This could cause another Black Death pandemic, although improvements in cleanliness, healthcare, shelter, and nutrition should prevent fatalities from reaching 14th century proportions.

Nevertheless, in this age of global travel, the disease could spread around the world in weeks, exacting a greater overall death toll.

Modern Cases of Black Death

Environmental Factors

High numbers of rats and animals in urban areas may also contribute to a future pandemic. Squirrels are particularly good carriers of fleas that transmit the disease. Pets and livestock can become infected as well, although they tend to die quicker.

Animals wouldn't be required if the deadlier flu-like version of the Black Death pathogen became widespread (pneumonic plague), and human fleas and body lice may cause an even quicker spread in populations where cleanliness is lacking.

Perhaps the most likely prelude to another Black Death pandemic would be environmental change. A colder climate over long periods could lead to crop failure, malnutrition, and starvation. Over-population or disruptions to the food supply could equally lead to a lack of food.

As with the original pandemic, malnutrition opens the door to disease by weakening the immune system. Although global warming is pushing temperatures in the opposition direction, a catastrophic event such as a nuclear explosion, asteroid impact, or widespread volcanic activity could lower global temperatures by filling the atmosphere with dust and blocking out the Sun's rays.

Smaller changes in the climate could also enhance the rate of infection. While wetter and warmer weather is not a cause of malnutrition, it does allow bacteria to grow quicker. In Central Asia, a one degree rise in the average annual temperature increased Black Death prevalence by 59%.

A particularly effective combination is warmer winters and cooler, wetter summers. Man-made global warming or El Niño effects could easily provide favorable conditions in several regions.

Plague doctors wore elaborate costumes to prevent infection, and victims doors were marked to warn others away.

Plague doctors wore elaborate costumes to prevent infection, and victims doors were marked to warn others away.

The Black Death Today

In the 14th century, people blamed the Black Death on God's anger and set about murdering minorities who they thought were to blame. This included Jews, lepers, Roma, and foreigners of all description.

In the 21st century, we understand the danger that microbial organisms pose to our health, so it is unlikely that such extreme prejudice would re-emerge. However, with the advent of international news and media, we are more attuned to events elsewhere in the world than at any other time.

If an epidemic were to arise in India, for example, one could expect discriminatory behavior against ethnic Indians in other countries, even if they had not traveled from infected areas. Indeed, during the COVID-19 pandemic, violence against Asian Americans increased in the US.

The act of painting a cross on the homes of the infected is another example of discriminatory behavior that would probably not be seen today. Infected people would be advised to remain in their homes and our understanding of bacterial transmission should be enough to prevent (a majority of) people from carelessly infecting others.


Despite there being no licensed vaccine for the Black Death, the chances of another pandemic are slim. Infection and fatality rates have decreased since the 14th century due to improved sanitation and nutrition, better protection against adverse weather, and effective antibiotic treatments.

For another pandemic to occur, one or both of the following would be required:

  1. The evolution of a drug-resistant strain of the Yersinia Pestis bacterium.
  2. An environmental catastrophe causing widespread detriment to human health.

Although these threats are quite real, there are other contagious diseases that present a greater danger. These include Covid-19, Avian Flu, Malaria, Hantavirus, West Nile virus, and Dengue fever. For example, it is predicted that global warming will soon allow Malaria to return to Europe. Indeed, warmer and wetter temperatures as well as over-population will contribute to a greater number of pandemics in the future.

Additional Sources

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2013 Thomas Swan


Thomas Swan (author) from New Zealand on July 28, 2015:

Thank you for your very informative comment Raevyn14.

Raevyn14 from Tecumseh, Oklahoma on July 28, 2015:

The idea of having another epidemic like that of the 14th century is unlikely. There are treatments to the 3 types of plagues. Vaccinations, however, have been proven ineffective to the Pneumonic plague. Here in the US there are fewer than 7 cases of plague a year. There are very powerful medications that take care of the plague in 7 days.. If you don't want the treatments.. Then with the Bubonic plague you have less than 7 day before the disease takes hold. The Pneumonic plague can take 3 days 'fore the disease to take over the lungs. Septicemic plague, however, can take 1 day for symptoms to appear and its the quickest of them all because by the time you show symptoms, it takes over.

Thomas Swan (author) from New Zealand on April 26, 2014:

Thanks Alicia. I hope so too. Your comment is quite coincidental, as I was thinking about this topic again only yesterday. There was a story in the news about a man who was finding rats in his attic, some as big as cats. The number of rats in developed areas may be on the rise, and that could increase the (small) chance of another outbreak.

Linda Crampton from British Columbia, Canada on April 25, 2014:

This is a useful and very interesting hub. It's also thought provoking! I hope the world doesn't face a black death pandemic again.

Thomas Swan (author) from New Zealand on October 03, 2013:

Thanks Michelle. I agree that if an epidemic were to happen again, it would probably begin in the developing world.

Michele Travis from U.S.A. Ohio on October 03, 2013:

Another very interesting hub. I think there is a possibility that this epidemic can happen again. For example, the increasing percentage of people living in severe poverty in countries like Africa. Or people who have had to flee their homes due to wars, like Syria and are living so close together and drinking water that is not clean.

There are a few possibilities, I am not sure. Just thinking about it.

Thomas Swan (author) from New Zealand on September 26, 2013:

That's a great point wilderness. It rings a bell with me too, but I didn't think of it when writing this hub. I believe they hated cats because of their association with witches, and that association probably arose due to Christianity vilifying "pagan" belief systems. The Egyptians worshipped cats, so that might be the source of it all.

Thomas Swan (author) from New Zealand on September 26, 2013:

Thanks jonny, I suppose it's one of many things we could do to improve our world. It always amazes me how the Earth provides us with all the energy we could ever need (sun, wind, geothermal, tidal, etc) and we resort to burning fossil fuels instead. Thanks for the info on humanure.

Dan Harmon from Boise, Idaho on September 25, 2013:

A well written and interesting hub - thank you.

In researching for a hub on Halloween, I came across a suggestion that humanity may have contributed to the black death in a more definitive manner. During that period in our history (European) there was a huge fear of cats, including the house cats we keep as pets today. Cats were routinely hunted down and killed, to the point that they were nearly wiped out throughout much of Europe - cats that in a densely populated area are a major factor in controlling rat populations.

Did we, by meddling with ecological balances, contribute to the epidemic? An interesting thought if nothing else, and shows just how dangerous that can be.

jonnycomelately on September 25, 2013:

Not an uncommon response to the suggestion, Thomas, and quite understandable. However, when using the Humanure method, as practised and written about by Joseph Jenkins in his "Humanure Handbook," I can ascertain there is absolutely no problem with smell.

The method is a wonderful education for our modern world, which has benefited enormously from the "flush" system since it was introduced in the 19th century. That was when the world had a population of less than 2 billion. Now we must research many areas of our relatively comfortable existence and find more sustainable and healthy methods to use the limited resources like water, fertilizers and soils.

A result of such changes will be a more healthy environment and reduction of water-borne diseases.

Thomas Swan (author) from New Zealand on September 24, 2013:

That sounds interesting jonny. I don't know a lot about that. I wonder how bad it would smell, but it seems like something that could be done in the developing world to prevent those diseases.

jonnycomelately on September 22, 2013:

You might be aware from some of my hubs and previous comments, that one of my big interests is more ecologically sensible infrastructure systems. One of those is sewerage. Composting excreta, ( Google "Humanure" ) instead of mixing it with fresh, potable water, can prevent the spread of water-borne diseases like cholera and typhoid. Compost can be fed back into agriculture when done properly, safely and with the recycling of important plant nutrients. So this is one way at least smaller communities could work towards "sustainability" and healthy lifestyles. You are not going to get huge metropolises going down this big change in the near future, but for local communities, wishing to take charge of their own needs, it could be a big benefit to their survival.

In my humble opinion.

In my opinion.

Thomas Swan (author) from New Zealand on September 22, 2013:

Thanks jonny, glad you liked it.

Good point chefsref. While our medical knowledge, nutrition, sanitation, and international response to famine makes us less susceptible to pandemics, population density and travel will work in the opposite direction. It gives the impression that if a `superbug' were to get through our defenses, it could pretty much wipe out everyone.

Lee Raynor from Citra Florida on September 21, 2013:

Excellent Hub

I think there is a bigger point behind this. With the increase in the number of people on Earth, the population density in cities and easy human mobility it seems inevitable that some untreatable disease is likely in the future. It may not be the Plague but there are plenty of diseases to choose from

jonnycomelately on September 20, 2013:

Excellent presentation. Thank you Thomas. Most interesting.

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