The Black Death
Your questions answered
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 Types of Transmission
• Bubonic – caused by affected alea biting 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.
Bad Lung!
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
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.
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.
Why did the plague recur sort of
regularly?
• The flea-bearing rodent reservoir of disease was
eventually succeeded by another species. The Black Rat
(Rattus rattus) was subsequently displaced by the
bigger Brown Rat (Rattus norvegicus).
• The brown rat was not as prone to transmit the germbearing 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.
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.
Natural Acquired Immunity
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/Bl
ackDeath.aspx
Any other questions?