The bubonic plague, also known as the Black Death, is a zoonotic disease that has a very high efficiency in its transmission. It spreads easily and the mortality rate is high. This plague is caused by a bacterium named Yersinia pestis; the transmission occurs in a cycle: this bacterium is transmitted to the human body by a bite from the vector which is a flea; the flea gets infected by sucking the blood of an infected rat. Others ways humans get infected with this disease include improper handling of infected animals and breathing in infectious materials, which is an uncommon means of transmission.
The symptoms of bubonic plague are headache, fever, vomiting, painful and swollen lymph nodes. At an advanced stage of bubonic plague, symptoms include heavy breathing, continuous vomiting of blood, aching limbs, extreme pain caused by the decomposition or decay of the skin, extreme fatigue, gastrointestinal problems, delirium and coma.
The spread of this plague was rapid because of some factors, the presence of these factors served as catalysts. Among these factors are environmental, biological and climatic factors:
Increased rat population
The pathogen Yersinia pestis is primarily a bacteria of rats. It survives amidst rats; hence increased rat population will lead to its successful thrive. The increased population also caused migration of rats alongside traders who were moving from one coast to another in ships. Also expanded trade across Europe which required traders to move from a place to another facilitated the rapid movement of the disease across the continent and beyond.
The abundance of adult fleas
Adult blood-sucking fleas which are the vectors of bubonic plague caused the rapid spread of the plague. They transmit the bacteria from rats to rats, and from rats to humans. The increased population of the fleas increased also potential infections of humans.
Lack of medical knowledge and basic scientific awareness
The people of the middle ages were ignorant of the impact of parasitic microorganisms on health. They do not believe or have any knowledge of the ability of microscopic organisms in causing diseases, hence another major reason for its rapid spread. Instead of finding solutions, the Medieval people were blaming some other sources like miasma (that is bad air), foreigners in the land, minority groups like the Jews and Gypsies, and societal wickedness which has invited the wrath of God in form of the bubonic plague.
Climate
Wet climates – heavy rainfalls and floods were also responsible for the increased spread of the plague. It was believed that heavy rainfalls which resulted in flooding could have been responsible for the migration of the rodents as well as human beings, thus carrying the disease-causing bacterium with them as they move along well-established roads and routes into towns and cities.
Lack of sanitation
Apart from the other factors that aided the spread of the plague, how people lived was also a great contributor. Irregular bathing, dirty clothing and beddings were normal for those living in a peasant environment. This attitude led to an increase in the population of rats and fleas, as the roofs of the homes provide suitable and comfortable homes for the rats and the dirty clothing, a harbour for the fleas.
These are the factors that led to the rapid spread of the infectious and deadly bubonic plague.