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Comment by pdevr | Hacker News Reader

As far as I understand it, they used 25 human and 12 squirrel samples. Comparison was done among medieval red squirrel strains, medieval human strains, and modern red squirrel strains.

Finding: medieval red squirrel strains were closer to medieval human strains than to modern red squirrel strains.

Inference: In medieval England, leprosy spread between red squirrels and people.

Problem with the inference: If they used modern human strains too and then compared them all, it would have been a complete study.

Are modern red squirrel strains closer to modern human strains than to medieval red squirrel strains? What kind of differences are there? Is it that they evolved independently from medieval times to modern times and thus appear different? Lots of questions are unanswered.

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> If they used modern human strains too and then compared them all

Presumably the number of leprosy cases originating in modern England is near zero, so actually procuring relevant strains seems impossible, no? I can't imagine that comparing random strains from places around the would would yield interesting results.

When we are only talking about a few samples in each group, 4 cases every few years seems fine.. I would hypothesize that many of the symptomatic cases are people who are foreign but exposed to UK endemic leprosy. Of course to establish how true that is means there are more data points to collect for cases with foreign contact and the involved lands.

I looked it up before I posted, and it's actually the opposite: the overwhelming majority of cases are from visitors to the UK who contracted the illness outside the country. The last confirmed case of leprosy being contracted in the UK was in 1953.

It is very low indeed, and a large percentage of the cases are involving strains from other countries, but hopefully the number is not real zero[1], even after discounting the strains from other countries.

[1] https://bmjopen.bmj.com/content/6/5/e010608

Not only that, but is it really the case that genetic material survives for 600 years? Can we really say, 'we know that these 12 samples are from red squirrels 600 years ago'?

> "With our genetic analysis we were able to identify red squirrels as the first ancient animal host of leprosy," says senior author Verena Schuenemann of the University of Basel in Switzerland.

Yes, it can https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3685887/

Thank you for the link.

> However, under favorable environmental conditions, for example when tissues are frozen or become desiccated quickly after death, these processes become inhibited before the complete destruction of all DNA endogenous to the organism.

Do you think there are 12 red squirrels in Winchester that were frozen or desiccated 600 years ago?

While Brexit has not improved food quality in Britain, I'm sure some well-preserved dead squirrels remain in the area. Also, Winchester is not that far from the Isle of Wight, one of the red squirrel strongholds

https://www.wildlifetrusts.org/where_to_see_red_squirrels

I'm out and about all the time, walking, I go to various places, and yet hardly ever find any signs of dead animals. Most recently I have saw a dead dear (roadkill), and it has now decomposed pretty completely after 2 months.

I don't see how 1 red squirrel dies 600 years ago, and we still have its remains today, nevermind 12 of them! All from Winchester!

Old churches, castles? Crypts, attics?

It's unlikely, right?

https://www.wikipedia.org/wiki/Grade_II*_listed_buildings_in...

Here's a list of medieval buildings in Winchester. There are 30-40 buildings old enough. Hard to imagine red squirrels choosing to die in these places, not being eaten by other critters, and then remaining undiscovered by cleaners all this time, only to finally become historical DNA samples.

> Back then, squirrel fur was used as a fine lining for clothes and some people also had pet squirrels. They were particularly popular with women.

from https://www.bbc.co.uk/news/articles/cj7mry8yvrmo

We are likely not talking about whole squirrels, but bits and pieces of them found on the burial sites.

I guess that proves it! :) /s

Thanks for the exchange.

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