MadSci Network: Microbiology

Re: How many people recovered from Black Death (Bubonic Plague)

Date: Mon Feb 22 12:01:53 1999
Posted By: Michael Maguire, Faculty,Case Western Reserve Univ.
Area of science: Microbiology
ID: 918741314.Mi

1.	Where did the rats get the bacteria?

Yersinia pestis is the bacterium that causes both bubonic and pneumonic 
plague, two different forms of the same disease.  It can live in rodents 
of all kinds, not just rats.  The rats get the disease also.  It can be 
transmitted to humans by a) rat bites or touching infected rats 
(uncommon), b) being in a dwelling or area that is not clean (lots of 
dust, rat droppings, etc.) and inhaling dust particle which also have some 
bacteria in them, c) flea bites.  The fleas are common on rodents, and get 
the bacterium when they bite the rats to eat.  They do not get the disease 
but can carry the bacterium for several days, during which time they may 
bite a human also, particularly if the human hasn't bathed or lives in a 
poorly cleaned, ventilated dwelling.  

Generally you get bubonic plague (skin sores and eruptions [called buboes, 
hence bubonic], internal hemorrhaging, shock due to massive internal cell 
death) from bites so that the bacterium directly enters the blood or 
tissue.  You get pneumonic plague (congested lungs, less body-wide 
infection) from inhaling the bacterium.  Actually, most people in the 
middle ages died of pneumonic plague not the bubonic form, but still, the 
same bacterium is causing the infection.

The bacterium is always around.  For reasons we do not understand even 
today, sometimes the conditions are right for a massive explosion of the 
rodent population and overcrowding.  This favors spread of the disease 
among the rodents.  They then come into contact with humans.  Plague is a 
disease of the growth of cities.  It was not known prior to the 13th 
century.  There might have been plagues earlier but very rarely, never at 
the size of the middle ages.  But for the first time in human history, 
cities began to grow rapidly in the 1200's and by the middle of the 
1300's, some were very large.  They were extremely crowded, with open 
sewers if they had sewers at all, poor water supplies that were always 
contaminated with some sewage, and overall, extremely poor hygiene.  In 
addition, bathing during the 12-1400's was considered unhealthy, so people 
and their clothes were usually great for fleas, which would also help 
spread the disease.  Plague is relatively rare now primarily because of 
better sanitation and quick control if cases are seen.

2.	How many people died in each family?

	Most.  Whole cities were depopulated.  It was estimated that 
Europe has a population if about 75 million in 1346, the year of the first 
major plague.  By 1350, only 4 years later, after several rounds of the 
plague, at least 25 million people had died, or 1/3 of the population.  
London's population fell from 60,000 to 25,000, Hamburg's fell by 50%, 
Bremen's by 2/3.  In 1665, another plague hit London (and had hit 
continental Europe the previous year), and 100,000 people died in less 
than a year.  The epidemic stopped probably only because a great fire 
swept over most of London, destroying houses (and the rats and fleas) and 
especially thatched roofs, which are a heavenly dwelling for rats and 
especially fleas.  This got rid of a lot of the carriers of the disease 
and also greatly diminished the density of the population.  Plague was not 
just in Europe.  China had several epidemics from 1200 to 1350 and its 
population decreased from 125 million to 60 million by about 1350.

3.	How many people died from Black Death after the 1900`s?

	Not that many.  There were small outbreaks in New Mexico among the 
Navajos in the 1980's, in Ghana in 1908 and 1924, and between 1975 and 
1985 in Madagascar, Uganda, Tanzania, Bolivia, Brazil, Peru, Burma and 
Vietnam.  In all cases, no more than a few hundred and usually well under 
100 people died.

4.	Is there a cure?

	Yes, it's a bacterium, so antibiotics work fairly well.  Current 
recommendations are streptomycin plus a tetracycline in combination.

5.	What do you find most interesting about Black Death?

	What's most interesting to me is that it is a disease of the 
growth of cities.  This is also true of Hansen's disease (leprosy), 
tuberculosis and syphilis.  Leprosy was not known until the 1100's (what 
the Bible calls leprosy is not true leprosy but an unknown disease that is 
definitely not leprosy).  Tuberculosis was very rare and syphilis was a 
minor disease of Caribbean and S. American Indians, but which proved quite 
deadly in the early 1500's in Europe.  There are a lot of pathogenic 
(infectious) bacteria on Earth, but many are never a threat to humans 
until exactly the right conditions are met for their growth to a point 
where lots of people get infected at once, then we get an epidemic.  The 
growth of cities is one example where several bacterial diseases found a 
way to grow better than ever before.  The advent of air-conditioning and 
water cooling towers has promoted growth of some other types of bacteria 
that can cause lung infections (Legionnaire's disease and several others).

As another example, in the 1980's, there was an outbreak of a type of 
pneumonia caused by Hantavirus among the Navajos in New Mexico and 
Arizona.  It was caused by an unusually wet and mild winter, which led to 
a very abundant pinon nut harvest from the pines, which provided an 
unusually abundant food supply over the winter and in spring for field 
mice, which increased in population several times and then, with the food 
running out, invaded human dwellings in search of food.  The virus resides 
in mice rather commonly, but rarely infects humans because of lack of 
contact.  In this case, the mice came in contact with a lot of people.

Bacterial and viral infections are not just from occasional interaction 
with a bacterium or virus, but can be increased or decreased by our 
actions, our culture and changing societies (how we live together).  

The Coming Plague (1994) Laurie Garrett, publ. by Farrar Straus and 
Giroux, New York.
Man and Microbes (1995) Arlo Karlen, publ. by Simon and Schuster, New York

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