How did the plague spread from human to human?
The plague, specifically the bubonic form caused by the bacterium Yersinia pestis, was predominantly transmitted from human to human through infected fleas. Here's how the spread occurred:
1. Interaction with Infected Rodents: The plague primarily originated in wild rodents, such as rats, squirrels, and marmots. These animals carried infected fleas that transmitted the bacteria to humans.
2. Infecting Fleas: When an infected rodent is bitten by a flea, the bacterium Yersinia pestis multiplies within the flea's digestive system. This can cause the flea to become blocked and unable to feed properly, leading to an increased tendency to bite multiple hosts in search of blood.
3. Human Flea Bites: Infected fleas jump from rodents onto humans and bite them, injecting the Yersinia pestis bacteria into the human bloodstream. The site of the flea bite usually develops into a swollen and painful lymph node, known as a bubo, which is a hallmark symptom of bubonic plague.
4. Spread Through Coughing and Sneezing: In some cases, pneumonic plague can occur when the plague bacteria reach the lungs and cause symptoms like coughing and sneezing. If an infected person coughs or sneezes near another person, the bacteria can be transmitted through respiratory droplets, leading to person-to-person transmission.
5. Contact with Infected Materials: The plague can also be spread through contact with infected materials or bodily fluids, such as the pus or blood of an infected person or animal. This type of transmission can occur during medical procedures, handling infected carcasses, or close contact with an infected person's belongings.
It's important to note that the transmission of the plague from human to human was most prevalent during medieval pandemics, such as the Black Death, where overcrowding, poor sanitation, and lack of medical knowledge contributed to the rapid spread of the disease. Modern public health measures and antibiotics have significantly reduced the risk of plague transmission and outbreaks.