27 Devastating Infectious Diseases

Causes And Effects Of The Black Death

There are various estimates of how many people died during the 1348-49 outbreak. Most historians believe between a third and half of the population were killed by the Black Death. The population of England at the time of the Black Death is estimated to have been around 6 million, so that means approximately 2 to 3 million people died.

Despite the scale of the fatalities, there is evidence that there was some sort of organised response from local government. Mass graves of victims have been found from the Middle Ages. The way the bodies are carefully laid in side by side suggests bodies were treated respectfully and in a dignified way.

A result of the high mortality rateclosemortality rateThe percentage of people who would normally die from a disease. So a disease with a mortality rate of 50% would mean an average of 50 people would die out of every 100 infected. Was a shortage of workers. This led to rapid wage rises as landowners had to compete for workers by paying more. In 1351 a law was introduced to force wages to go back to the levels they had been at before the Black Death. This was one of the causes of the Peasants' Revolt in 1381.

As no one knew exactly what caused the Black Death, they could do little to stop future outbreaks. There were further Black Death cases throughout the Middle Ages and beyond. There was another significant outbreak in 1665, particularly affecting London. This outbreak shows there had been no real increase in understanding about what was really causing the disease or how to prevent it.

It wasn't until the work of Louis Pasteur and Robert Koch in the 1800s that it was discovered germs are the cause of disease. The plague bacteria was finally discovered by Alexandre Yersin in 1894. The bacteria was named after him; 'Yersinia pestis.'

From The Black Death To Spanish Flu And Smallpox, A Brief History Of Plagues

No matter where you look up the meaning of the word "plague", it's never a good thing. It can be confusing, because as a verb, plague means "to cause continual distress", yet as a noun, it means a deadly disease that spreads very quickly – what we would today call a "pandemic". It can also refer to one specific disease, Yersinia pestis. 

On top of that, a plague can refer to a large number of insects or animals in one place that are causing a lot of damage, like the locusts currently swarming in east Africa. 

In this article, we'll talk about the plagues, or pandemics, that humans have battled with throughout history. 

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Black Death

The worst plague in history was the Black Death, which may have killed up to 200 million people. This was caused by a bacteria, Yersinia pestis, that first hit Europe in the 1340s. 

People still disagree over where it came from, but the most common theory is that it first emerged in Asia, in a certain type of flea that lived on rats. In fact, when scientists in the 1900s were looking for the cause of a similar disease, they came to Hong Kong as part of their investigation. 

Back in the 1300s, life was pretty dirty, as people didn't know anything about hygiene. They also didn't have much medical knowledge – they had never heard of antibiotics or quarantine. This meant that the plague killed around 90 per cent of the people it infected, and in some cases, it killed everyone it infected. But this didn't wipe it out.

Several waves of the Black Death swept the globe and killed hundreds of millions of people.

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Two more deadly waves of the plague hit in the 1500s and 1800s. In fact, scientists think that it may have been around before the 1300s, as there are records of a similar disease in Rome in 146AD, known as the Justinian plague.

The symptoms of the plague were awful. It started with a swelling in the lymph nodes under the armpit or in the groin, until they were about the size of an apple. Once the swellings burst, people had a fever, vomited blood, and soon died.

Spanish flu

After the devastation of the first world war came the Spanish flu. It did not actually come from Spain, but this was where it first became bad enough to be noticed. It killed up to 40 million people – more than all the deaths of the first world war. It spread across the world, aided by the movement of  hundreds of thousands of soldiers to far-off battlefields. 

It started out like a normal cold, so people were not too worried about it. But then those who were infected developed pneumonia, a lung condition which makes breathing difficult. After that, victims eventually suffocated. 

No one knows where the Spanish flu started, but recent studies show that the virus may have emerged when strains of pig and human flu infected the same host, and their genes combined to create a new mutation. 

Medical workers wore masks to avoid the Spanish flu at a US Army hospital in 1918.

Photo: Shutterstock

Smallpox 

There is no doubt that plagues changed the course of history. They caused empires to fall and new ones to arise. Smallpox first emerged around 68,000 years ago. We have no idea how many people it has killed, but we do that in the 20th century alone it killed around 500 million people. 

Smallpox was introduced to the Americas by European colonisers in the 1400s. It was responsible for the fall of the Aztec and Incan empires, and killed up to 90 per cent of the Northern Native American population – allowing the Europeans to steal the land and claim it as their own.

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Smallpox was the leading cause of death in the 18th century. And, like all good plagues, it was awful, causing sufferers to break out in small blisters all over their bodies that caused them great pain.

People did notice, however, that once someone had survived smallpox, they never got it again. So, in the 10th century, people in China began taking some pus from the infected blisters and scratching it into their own skin. This allowed the body to learn the virus' code and build immunity to defeat it. In 1798, an British doctor, Edward Jenner, developed a vaccine. In 1966, the World Health Organisation began a global vaccination campaign to wipe out smallpox for good. The last-ever case was diagnosed in 1977. Smallpox is one of only two infectious diseases to have been completely stopped. Hooray for vaccines!

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