[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

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...

The code/models we used are available online for one of the outbreaks (Barcelona 1490) 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... 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...

Model-based analysis of an outbreak of bubonic plague in Cairo in 1801: http://rsif.royalsocietypublishing.org/content/14/131/201701...

[mathattack]

Great paper. Certainly gives credence to the idea that All Conclusions Are Provisional. (Also will make me panic the next time the kids get head lice)

[BorisVSchmid]

Thanks! You might be able to postpone the panicking. Although I haven't looked into head lice (we specifically looked at body lice), this redditor had some links in that head lice apparently are less likely to carry diseases.

https://www.reddit.com/r/news/comments/7qopqf/black_death_sp...

[maxerickson]

The lice would also need to be coming from a human with the plague, right?

And we can treat the plague today.

[archgoon]

So the original theory of the black death was that the disease originated in Asia, and was borne to Europe via rats on ships. Is the new theory arguing that it was the sailors transmitting it instead, or is the origin of the black death in Europe now unknown? Also, is the paper arguing that rats are not vectors for the disease?

[BorisVSchmid]

Paper is online now :-).

I also put a popular science summary of the paper online here: https://medium.com/@boris.schmid/human-ectoparasites-and-the...