The Black Death

1. The Black Death Your questions answered

2. Yersinia Pestis • The plague is caused by a bacterium – Yersinia Pestis. • Yersinia Pestis is easily destroyed by sunlight and drying but it can still live up to an hour in the air. 

3. 3 Types of Transmission • Bubonic – caused by affected aleabiting a human. Lymphatic system > swollen and tender lymph glands, fever, headache, chills, and weakness • Septisemic– occurs when bacteria numbers multiply in the blood of the victim via inhalation or initial flea bite. [bacteria] increases in blood > fever, chill, abdominal pain, shock, bleeding into the skin and organs. • Pneumotic- caused by inhaling the bacteria associated with the "Black Death." It begins as a severe pneumonia with high fever, chills, and cough.

4. Bad Lung!

5. Y. Pestis • Is epizootic – this means it causes a disease that is widespread throughout an animal population. • Rodents are its natural reservoir. • Worldwide, approximately 1,000 to 5,000 human cases of plague and 100 to 200 deaths reported annually to the World Health Organization

6. What happens to animals infected with Y. Pestis? • Depends on the animal – and the parasitic relationship between host and parasite. • Dogs – seem to recover quickly with sub-clinical symptoms • Cats – can recover but some fatality • Mountain lions – quite susceptible, fatal • Rodents – high fatality in rats. • Marmots – in China and suseptible.

7. How do plagues begin? • Rats baring plague infected fleas were transported by the Silk Road from China and along the trade routes to Europe • People began to move from rural areas which were isolated, into larger towns and cities – increase in Urban density. • These rats and their fleas entered new environments and exploited them – their population increased. • Ignorance about hygiene and germ theory further exacerbated the situation. • Low immunity in population due to unbalanced diet and lack of food and hygiene.

9. Why did the plague recur sort of regularly? • The flea-bearing rodent reservoir of disease was eventually succeeded by another species. The Black Rat (Rattusrattus) was subsequently displaced by the bigger Brown Rat (Rattusnorvegicus). • The brown rat was not as prone to transmit the germ-bearing fleas to humans in large die-offs due to a different rat ecology. • The dynamic complexities of rat ecology, herd immunity in that reservoir, interaction with human ecology, secondary transmission routes between humans with or without fleas, human herd immunity, and changes in each might explain the eruption, dissemination, and re-eruptions of plague that continued for centuries until its unexplained disappearance.

10. How did the Plague end? 1. Natural acquired immunity. Eventually the plague simply couldn't affect as many people. Most everyone was immune after it ran its course through Europe. The ones who got it and didn't get an immunity were dead. All that were left to infect were the ones that had managed to not catch it at all. 2. Communities got better at dealing with it – isolation measures. 3. Population of fleas and rats reduced so that it was no longer supported widely, and ceased to be epidemic.

11. Natural Acquired Immunity

12. Why was Milan less affected than other places? • "In Milan, to take one of the most successful examples, city officials immediately walled up houses found to have the plague, isolating the healthy in them along with the sick. Venice took sophisticated and stringent quarantine and health measures, including isolating all incoming ships on a separate island. But people died anyway, though fewer in Milan and Venice than in cities that took no such measures” The entire paper can be found at: http://www.militaryhistoryonline.com/general/articles/BlackDeath.aspx

13. Any other questions?