The Black Death 1346-1353: The Complete History

In 1870, scientists discovered bacteria as a source of illness and began to identify pathogens. This advancement led French and Japanese researchers to identify yersinia pestis, the bacterium that causes plague, in 1894. They also noted that rats were the source of this bacteria. This discovery occurred in response to a plague outbreak that started in in the western Chinese province of Yunnan, spread to Canton and Hong Kong, and led to many casualties. Canton and Hong King were important center of trade for western colonialists who took an interest in combatting plague.

In the early 20th century, the Indian Plague Research Commission discovered that rats carried these bacteria and that they were transmitted through flea bites. Because homes were often infested with rat colonies, once the plague depleted the rat population, the fleas moved to human hosts. Rat fleas carry high levels of the bacteria, and when the insects develop a stomach blockage, they spew infected blood into bite wounds on their hosts. Fleas with this stomach blockage become ravenous and, thus, bite innumerable times. Rat fleas are especially susceptible to developing such a blockage.

The commission also investigated plague’s epidemiology. Findings show that it takes between 10 and 14 days for a rat colony to die off due to plague. The fleas then move to human hosts, who become infected with plague in three to four days; it takes approximately three to five days for humans to exhibit symptoms. Thus, the first human infections typically appear within 16 to 23 days, while death occurs within 20 to 28 days. Those who visit the homes of the ill are most likely to become infected when rat fleas contaminate their clothing or when they are bitten at the victim’s home. Travelers carrying the rat fleas in their baggage and/or clothes, therefore, unknowingly carried plague to other villages, towns, and cities.

Plague was also able to travel hundreds of miles along routes of trade because the infectious rat fleas had the ability to survive on grain that was being transported over global networks of trade. Infectious rat fleas survive well in moist climates, so the humidity of ship travel facilitated their survival and transport. Archeological and linguistic evidence shows that black rats were found all over pre-modern Europe, including the colder northern areas. Thus, they were the primary carriers of the bacterium that caused the Black Death during the European Middle Ages.

Plague can take several forms, but the most common form in the medieval period was the bubonic plague that is carried by rats and spread by fleas. This form of plague inflects one’s lymph nodes. In some cases, it moves into the victim’s blood stream, which can cause under-skin hemorrhaging, resulting in dark splotches on the body such as those described in the late medieval account authored by Florentine eyewitness Giovanni Boccaccio. Plague also comes in a pneumonic form when the bacteria reach the victim’s lungs after the person has been infected with the bubonic variety. This form can also be transmitted from person to person via respiratory droplets, but these cases were rarer and restricted to household members and caregivers for the sick. Women were more vulnerable to contracting this form of infection because they were often primary caregivers to the sick. This variety, known as primary pneumonic plague, was more contained, because the ill die swiftly, often before a cough develops, thus limiting their ability to spread the illness to others. Pneumonic plague, therefore, was not the primary form of plague spread during the Black Death.

The Indian Plague Commission’s research also showed that the pathogen had a lower mortality rate in densely populated cities than in small villages. Mortality rates in the countryside proved highest. Urban areas were, thus, not so hard hit as researchers previously believed. Population density is significant in the case of plague mortality because

Rats are social animals that define and defend their territories. This means that in the countryside, at least one rat colony will normally be co-resident with a household, whereas in urban areas several households will usually crowd together within the territory of the rat colony. (33)

In other words, there is a smaller rat/flea-to-human ratio in cities, and, hence, there are more human hosts on which hungry fleas can feast. Most of medieval Europe’s population was rural, with lower population density in the countryside than today; thus, these areas had higher mortality rates than Europe’s cities when the Black Death erupted. To be sure, many people died in dense urban areas, too, but small villages fared worse.

The first plague pandemic, sometimes called the Justinian pandemic, consisted of 15 waves between 541 and 767 AD. The second plague pandemic, which also took place in waves, is the Black Death of the 14th century. Evidence shows plague had a presence in parts of Africa and modern Yemen that spread to areas of Europe during this first pandemic via local plague foci in northern Africa and the Middle East, where it arrived with merchant caravans. Two factors led to the first pandemic’s end. First, the collapse of the western Roman Empire and Germanic migrations across Europe led to de-urbanization and a reduction in trade. Second, the rise of the Islamic Caliphate in the 600s to 700s “broke off almost entirely the exchange of goods and persons over the Mediterranean […]” (40). The first pandemic concluded because of these political developments that disrupted trade and, thus, the disease’s spread.

Plague also had a long history in the eastern hemisphere, where it made appearances in China and India. Benedictow identifies three foci as contenders for the Black Death’s place of origin. The first is the focus that runs along the shore of the Caspian Sea that crossed modern Russia and Kazakhstan heading toward the Crimea. Next is the focus that crosses the Caspian’s eastern side and enters Central Asia. Finally, there is a plague focus centered on modern Russia’s Siberian frontier that borders Mongolia, Outer Mongolia, and Manchuria in today’s northern China. Did the Black Death originate in East Asia or closer to Europe? Benedictow argues that surviving primary sources do not support the theory of Chinese origin. Rather, the Black Death originated in today’s southern Russia, along the Caspian’s northwestern shore, which was controlled by the Mongol Golden Horde. Russian chroniclers recorded information about a plague outbreak in 1346, and this information, along with other data, supports Benedictow’s assertion. This plague eventually reached the Crimean city and important port of trade, Kaffa, which was located on the banks of the Black Sea. The Italian city-state of Genoa controlled Kaffa, but in the mid-1300s, the Golden Horde besieged the city and brought plague. Sources indicate that a plague outbreak started in the military encampment around the city but soon breached the city walls. Because of illness, the Golden Horde retreated, and Genoese merchants fled to Italy, traveling through the Byzantine capital, Constantinople, unaware that they were taking bubonic plague with them and contaminating both cities.