How did the Black Death spread? It was spread by people along trade routes.
The Black Death is another name for bubonic plague, which is caused by a bacteria called Yersinia pestis. Y. pestis generally lives in fleas that feed on rats. When the flea bites the rat, the bacteria passes into the rat’s blood. However, sometimes it kills off all of the rat population and has to find another host. This is where it makes the jump from rats to people. The fleas are equally happy feeding on the blood of people and the bacteria has no qualms about infecting us. People washed a lot less frequently then than they do now and most people had fleas.
Y. pestis gets into the body either by inhalation or through a cut or bite from a flea. It can sense the surrounding temperature and when the temperature is 37°C, the temperature of many warm-blooded mammals, the bacteria activates. It changes its outer membrane so that it can’t be detected by the immune system and heads for the lymph nodes. If the bacteria comes across any immune cells, it injects them with toxins that deactivate them. The Y. pestis uses a molecule to absorb the body’s iron and it starts to replicate in the lymph nodes. The lymph nodes try to defend themselves and swell up, causing the buboes that give bubonic plague its name. The bacteria spread through the blood, in a similar way to cancer, and head for the lungs. Because there are so many bacteria travelling through the blood, the body goes into septic shock and the blood vessels start to leak. The level of blood drops, the blood pressure drops, and the organs shut down, killing the person. The infection caused gangrene and blackened tissue, which could be where the name Black Death came from.
These days, bubonic plague is treatable with antibiotics, but this has only been true for the last hundred years or so. There have been three main bubonic plagues throughout history: 541, 1347, and 1894. There were probably other plagues before this, but they were not so well reported. Each of these plagues started in a different place and had a different method of spreading. Let’s look at them in turn.
The 541 plague is also called the Justinian Plague because the Byzantine Emperor, Justinian I, caught it and survived. This plague appears to have begun with rats infected by Y. pestis in sub-Saharan Africa. The plague spread from there up through Africa along trade routes. Where people traded grain, there would be rats, and the rats were usually infected. Once the plague reached Africa, it travelled on boats across the Mediterranean into Europe. Egypt was the grain basket of the Roman (Byzantine) Empire and the grain was traded all around their Empire. Looking at the map of the first great plague is almost the same as looking at a map of the Eastern Roman Empire. This plague lasted off and on for 300 years and is estimated to have killed about 40% of the population, about 100 million people.
The second great plague, the one where it became known as the Black Death, started in the 1330s and lasted until approximately 1400. This plague seems to have started in Central Asia, probably in Mongolia. The bacteria travelled from there into Europe, brought by Genoese traders. It reached Europe in 1347 and within three years it had spread throughout all of Europe. This goes to show how trade routes had advanced over the years since the first great plague. It probably killed about 200 million people across Europe. The plague would reappear on and off for centuries, often in many major world cities.
The third great plague started in 1855. It began in Yunnan, China, which had become a center of immigration due to its wealth of copper deposits. These people carried the disease on with them. It had spread throughout southern China and large parts of India by 1894. As with the previous two plagues, this plague shows the world’s trade routes at the time. The first plague was limited to the Byzantine Empire, the second to Europe, but this plague went worldwide. Within twenty years it had spread to every inhabited country on Earth. It is estimated to have killed 15 million people worldwide and it wasn’t contained until 1959. Most of the people that died were in India.
So, how did the black death spread? It spread along trade routes and was carried by rats with fleas, or people with fleas. Once people were infected, they could pass the bacteria on by coughing. And this is what I learned today.
Sources
https://my.clevelandclinic.org/health/diseases/21590-bubonic-plague
https://www.realclearscience.com/blog/2014/02/how_does_the_plague_kill_people.html
https://emergency.cdc.gov/agent/plague/faq.asp
https://en.wikipedia.org/wiki/Plague_of_Justinian
https://en.wikipedia.org/wiki/Second_plague_pandemic
https://www.history.com/news/rats-didnt-spread-the-black-death-it-was-humans
https://www.livescience.com/worst-epidemics-and-pandemics-in-history.html
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