
Black Death 'spread by humans not rats' - curtis
http://www.bbc.com/news/science-environment-42690577
======
BorisVSchmid
Last author here. The paper itself comes out this week on PNAS, but the press
embargo is lifted already. When it comes out, you can find it here:
[http://www.pnas.org/cgi/doi/10.1073/pnas.1715640115](http://www.pnas.org/cgi/doi/10.1073/pnas.1715640115)

What we have done is compare the rise and fall of daily or weekly mortality
levels during plague outbreaks against three models of plague transmission -
two that are generally accepted (rat-borne plague and pneumonic plague), and
one that has been speculated about for a long time (human ectoparasites like
body lice and fleas). We allowed the models to achieve the best fit they could
within biological parameter constraints, and see how well each of these models
could mimic the observed mortality curve.

There is a bit more detail in this interview:
[https://news.nationalgeographic.com/2018/01/rats-plague-
blac...](https://news.nationalgeographic.com/2018/01/rats-plague-black-death-
humans-lice-health-science/)

The code/models we used are available online for one of the outbreaks
(Barcelona 1490)
[https://zenodo.org/record/1043924](https://zenodo.org/record/1043924)

A pre-review version of the paper is available as a poster here:
[http://www.mn.uio.no/cees/english/people/phd/katharrd/kd_yer...](http://www.mn.uio.no/cees/english/people/phd/katharrd/kd_yersinia_poster.pdf)
Note that we changed the lice model a bit since then, on recommendation of one
of the reviewers.

~~~
raphaelj
Could it be a combination of several transmission methods? Like rats + lice?

~~~
BorisVSchmid
That indeed could be. We didn't test mixed models of transmission, but we took
the first step here by testing all three models independently.

Xavier Didelot did some work on testing mixed models for two cities, 17th
century Eyam and 19th century Cairo. He did have to further simplify the
models though - there are some restrictions on how many floating parameters
you can have while the models are trying to converge to the parameter set that
results in the best match with the observations.

Epidemiological analysis of the Eyam plague outbreak of 1665–1666:
[http://rspb.royalsocietypublishing.org/content/283/1830/2016...](http://rspb.royalsocietypublishing.org/content/283/1830/20160618)

Model-based analysis of an outbreak of bubonic plague in Cairo in 1801:
[http://rsif.royalsocietypublishing.org/content/14/131/201701...](http://rsif.royalsocietypublishing.org/content/14/131/20170160.article-
info)

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tw1010
Attention-grabbing headlines and bad research has conditioned me to not update
my beliefs based on anything that I only briefly stumble upon like this. There
might have been a time when reading an article like this would blow my mind,
and make me excitedly share it with others who had a similar belief, but now
my first impulse is to just feel sceptical.

~~~
BorisVSchmid
Not a bad first impulse :-). It often pays in science to wait a few
years/follow-up studies before fully accepting something. What is thought to
be true in plague is especially fluid now with ancient DNA studies on human
remains coming out regularly, each with its own narrative on how to explain
the phylogenetic tree.

That said, there are some long-standing questions in plague research, one of
which is why the first and second plague pandemic were that much more lethal
than the third plague pandemic. Prior to the aDNA work, people speculated that
medieval plague was a different pathogen altogether, but that hypothesis has
been put to rest now. An alternative theory has been that plague could spread
through human ectoparasites, and we found a novel way to test that theory.
That resulted in this paper.

~~~
idanman
Could it be that by the third plague more people developed immunity and
therefore less were killed.

~~~
geezerjay
> more people developed immunity

Better yet, those who survived prior plagues were more likely to already be
immune to the disease, and evolutionary pressure led to a more resilient
population against this type of disease.

------
sillysaurus3
If you want to get into the mindset of what it was like to deal with the black
death, check out Plague Doctors:
[https://www.youtube.com/watch?v=oDz0OrRZOZ0](https://www.youtube.com/watch?v=oDz0OrRZOZ0)

~~~
JumpCrisscross
On the upside, Black Death survivorship may explain Europeans' relative
resilience to HIV (edit: smallpox) [1].

[1]
[https://www.nature.com/news/2005/050307/full/news050307-15.h...](https://www.nature.com/news/2005/050307/full/news050307-15.html)

~~~
IncRnd
If the contention of this page's article is true (BD spread by humans), then
the link you posted is more in favor of _smallpox_ being the cause of
relatively greater resistance to HIV in Europe.

------
toolslive
I think this was already known in the 90s. At least a plaque in the Antwerp
Zoo has already been stating this since the beginning of this millenium.

~~~
BorisVSchmid
You are right that there have been people speculating about it for a long
time, going back more than a hundred years. Some of the earliest reports are
from the time of the Indian Plague Commission, and there have been some
snippets of evidence since then.

One of the groups that is doing most of the research on body lice as vectors
of plague is the group of Didier Raoult. Michelle Ziegler made a nice summary
of that work here:

[https://contagions.wordpress.com/2016/11/17/the-case-for-
lou...](https://contagions.wordpress.com/2016/11/17/the-case-for-louse-
transmitted-plague/)

------
singhrac
Research clearly funded by rats.

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microcolonel
This may mean good things for the outbreaks in remote parts of Madagascar and
anywhere else one may occur, because the solution could be as simple as
sanitation and delicing.

~~~
BorisVSchmid
The 2017 madagascar one might actually have been a combination of rats and
pneumonic plague. But yeah, it is good to pay attention to all possible routes
of transmission and see where you can intervene.

------
ziotom78
There were several outbreaks in the centuries 14th-19th. Did the data used by
the author cover all the major ones? My impression is that it is easier to
recover data for the most recent outbreaks than for the older ones.

~~~
BorisVSchmid
There were indeed hundreds of outbreaks during those centuries. The outbreaks
we selected were the ones for which we could find daily or weekly mortality
records, as that gives you an epidemic curve that you can fit mathematical
model to.

We didn't use all of the cities for which we had outbreaks, but selected nine
that covered a large part of the time period, and a large geographic region.
Here is the list:

Givry, France, 1348. Florence, Italy, 1400. Barcelona, Spain, 1490. London,
England, 1563-1564. Eyam, England, 1666. Gdansk, Poland, 1709. Stockholm,
Sweden, 1710-1711. Moscow, Russia, 1771. Malta, Malta, 1813.

------
scentoni
PSA: "Plague is widespread in much of California, including in the Sierra
Nevada mountains and foothills. In a typical year, the Centers for Disease
Control and Prevention (CDC) reports about ten cases of plague in humans per
year in the western United States. However, during 2015, 16 human plague cases
were reported."

[https://www.nps.gov/yose/planyourvisit/plague.htm](https://www.nps.gov/yose/planyourvisit/plague.htm)

------
nukeop
Does this shed a new light on the mystery of why the area of modern Poland was
spared, remaining largely unaffected by the plague?

Also it makes a certain novel sound a little bit less realistic.

~~~
olavk
It seems to be an internet myth that Poland was laregly spared. Some guy over
at AskHistorians actully dug into the evidence:
[https://www.reddit.com/r/AskHistorians/comments/79dwua/why_d...](https://www.reddit.com/r/AskHistorians/comments/79dwua/why_did_poland_have_lower_rates_of_black_death/)
\- it is a fascinating writeup.

------
mc32
So I guess, one question this would raise, is, of modern infection, what is
the vector found?

Not that they must be the same, but at least they might have an explanation as
to why modern infections would be different from historical ones, if they are
any different.

~~~
BorisVSchmid
There are some studies that looked at the ectoparasites found during plague
outbreaks, but just finding an ectoparasite with plague-infected blood in it
doesn't tell you much yet on the importance of the transmission route.

Piarroux R, et al. (2013) Plague epidemics and lice, Democratic Republic of
the Congo. Emerg Infect Dis 19:505–506.

Laudisoit A, et al. (2007) Plague and the human flea, Tanzania. Emerg Infect
Dis 13: 687–693.

Ratovonjato J, Rajerison M, Rahelinirina S, Boyer S (2014) Yersinia pestis in
Pulex irritans fleas during plague outbreak, Madagascar. Emerg Infect Dis
20:1414–1415.

------
david927
Boris, thanks for answering questions here.

One more: has this raised any doubts that the Black Death was a Bubonic
Plague?

~~~
BorisVSchmid
Depends on how you mean the question. ancient DNA analysis has settled that
the first two plague pandemics were Yersinia pestis, so if your question was
on what kind of bacterium caused the Black Death - that is Yersinia pestis.

If it is about the manifestation of the disease (the clinical symptoms), those
we only know from historical descriptions and that is not something a model
can change :-). So yeah, many infected people would still have had buboes.
Buboes are also the expected result from plague acquired from fleas (whether
they were human fleas or rat fleas).

What might be less known is that there is a pretty high chance (10-20%) that a
person suffering from bubonic plague progresses to pneumonic plague. That
basically is a death warrant for that person, but it also means that he/she
might spread the disease further through air-droplets. If the conditions are
right, you might get a pneumonic plague epidemic intermingled with a bubonic
plague epidemic. Model-wise, that is one scenario we haven't looked into, but
we have seen something like that play out in Madagascar last year.

------
scentoni
Rodent Plague Surveillance in California

[https://www.arcgis.com/apps/ImpactSummary/index.html?appid=6...](https://www.arcgis.com/apps/ImpactSummary/index.html?appid=6627dfd8b7f1485cbdfda824965e49b3)

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brndnmtthws
I never really understood why people hate rats, but love squirrels. I think
rats are cool too.

~~~
astura
Most people hate squirrels, at least around here.

~~~
brndnmtthws
In NYC it's pretty common to see people watching them and taking pictures of
them.

~~~
dentemple
Those are tourists.

~~~
brndnmtthws
And what, they don't count as people?

~~~
geezerjay
They don't count as people who have to deal with squirrels. Bears are also
cuddly.

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hajile
Yet another paper discovers the obvious. The "cure" for the plague was 40 days
off isolation of affected homes or cities. Rats and fleas don't respect human
quarantines.

Another factor is rats. They are killed by plague just like humans. At least
one person should have noted large volumes of rats dropping dead everywhere,
but that isn't mentioned in writings of the time.

~~~
autokad
> " Rats and fleas don't respect human quarantines."

rats dont travel as much as you think, even within cities. only when the rats
piggy back on human travel, could they have spread the disease.

[https://www.nytimes.com/2015/04/26/magazine/the-rat-paths-
of...](https://www.nytimes.com/2015/04/26/magazine/the-rat-paths-of-new-
york.html)

"But feral cats won’t stray three blocks beyond where they were born, and few
mice will venture more than a hundred feet from their burrows in a lifetime."

~~~
hajile
If rats don't travel, then how do they spread the plague? If they do travel,
then quarantine would not work. If they travel with humans, then we would
expect to see massively higher infection and death rates among travellers due
to prolonged times with infected rats as they dragged them everywhere (where
is this evidence?) The plague spread across Europe at an enormously fast rate
(some believe that hemorrhagic fever with a separate bubonic outbreak in
Italy).

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aurelien
Maybe it spread from the sacramental bread eat in church ...

