Scientists find medieval plague outbreaks picked up speed over 300 years


Date:
October 19, 2020
Source:
McMaster University
Summary:
Researchers who analyzed thousands of documents covering a 300-year
span of plague outbreaks in London, England, have estimated that
the disease spread four times faster in the 17th century than it
had in the 14th century.



FULL STORY ========================================================================== McMaster University researchers who analyzed thousands of documents
covering a 300-year span of plague outbreaks in London, England, have
estimated that the disease spread four times faster in the 17th century
than it had in the 14th century.


==========================================================================
The findings, published today in the Proceedings of the National Academy
of Sciences, show a striking acceleration in plague transmission between
the Black Death of 1348, estimated to have wiped out more than one-third
of the population of Europe, and later epidemics, which culminated in
the Great Plague of 1665.

Researchers found that in the 14th century, the number of people infected during an outbreak doubled approximately every 43 days. By the 17th
century, the number was doubling every 11 days.

"It is an astounding difference in how fast plague epidemics grew," says
David Earn, a professor in the Department of Mathematics & Statistics
at McMaster and investigator with the Michael G. DeGroote Institute for Infectious Disease Research, who is lead author on the study.

Earn and a team including statisticians, biologists and evolutionary geneticists estimated death rates by analyzing historical, demographic and epidemiological data from three sources: personal wills and testaments,
parish registers, and the London Bills of Mortality.

It was not simply a matter of counting up the dead, since no published
records of deaths are available for London prior to 1538. Instead, the researchers mined information from individual wills and testaments to
establish how the plague was spreading through the population.

"At that time, people typically wrote wills because they were dying
or they feared they might die imminently, so we hypothesized that the
dates of wills would be a good proxy for the spread of fear, and of death itself. For the 17th century, when both wills and mortality were recorded,
we compared what we can infer from each source, and we found the same
growth rates," says Earn. "No one living in London in the 14th or 17th
century could have imagined how these records might be used hundreds
of years later to understand the spread of disease." While previous
genetic studies have identified Yersinia pestis as the pathogen that
causes plague, little is known about how the disease was transmitted.

"From genetic evidence, we have good reason to believe that the strains
of bacterium responsible for plague changed very little over this time
period, so this is a fascinating result," says Hendrik Poinar, a professor
in the Department of Anthropology at McMaster, who is also affiliated
with the Michael G. DeGroote Institute for Infectious Disease Research,
and is a co-author on the study.

The estimated speed of these epidemics, along with other information
about the biology of plague, suggest that during these centuries the
plague bacterium did not spread primarily through human-to-human contact,
known as pneumonic transmission. Growth rates for both the early and late epidemics are more consistent with bubonic plague, which is transmitted
by the bites of infected fleas.

Researchers believe that population density, living conditions and cooler temperatures could potentially explain the acceleration, and that the transmission patterns of historical plague epidemics offer lessons for understanding COVID-19 and other modern pandemics.

This new digitized archive developed by Earn's group provides a way to
analyze epidemiological patterns from the past and has the potential to
lead to new discoveries about how infectious diseases, and the factors
that drive their spread, have changed through time.


========================================================================== Story Source: Materials provided by McMaster_University. Original written
by Michelle Donovan. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. David J. D. Earn, Junling Ma, Hendrik Poinar, Jonathan Dushoff, and
Benjamin M. Bolker. Acceleration of plague outbreaks in the second
pandemic. PNAS, 2020 DOI: 10.1073/pnas.2004904117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201019155926.htm

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