Human Teeth Hold the Secrets of Ancient Plagues – The Atlantic

Zhang: This is what I find so fascinating. If the bacteria are largely the same, why dont we have Black Death anymore or big outbreaks of bubonic plague?

Krause: First of all, we changed our lifestyle quite a bit. We are just living in much more hygienic conditions. Plague is actually not usually transmitted between people, but between animals and people, and usually the vector is a flea. We dont live with mice and rats in the house as much.

Also, the type of rodents changed. In the medieval time, when the Black Death happened, we had a very large population of black ratsmuch, much bigger than today. And in fact, they were largely replaced by brown rats, Rattus norvegicus. Now, brown rats are very different in their behavior. They live in the sewage, and they live in the ground. They dont live under the roof. The black rat was called the roof rat. They were living where people stored their grain, and when people still had the grain storage in the house, thats where the rats were.

But people that do have exposure to animals, like people that live in the countryside, people that go hunting, they are usually the people that contract plague these days. Theres several cases in the U.S. every year. And there are warning signs if you go to the Grand Canyon: Dont feed the squirrels, because you could get plague. Its actually moving in the U.S. from the West Coast to the East Coast with rodent populations.

Zhang: I live in New York, so I guess we have that to look forward to at some point.

Krause: And you have a lot of rats in New York.

Zhang: Yes, but theyre brown rats!

Krause: Fortunately, yes.

Zhang: The spread of brown rats through global shipping routes is one of the big ecological stories of the past several centuries. Environmentally, its been devastating, especially for a lot of island ecosystems, so its really interesting to think about the role they might have played in spreading diseaseor not spreading it.

Krause: Some people speculate that the brown rat saved us from the plague. One of the mysteries is that the plague disappeared in the beginning of the 18th century, when you still have rats, when you still have hygienic conditions which are not great. What happens in Europe is that the new rat gets introduced. The brown rat arrivestheres some historical documentation around the 1720sand then it starts spreading. Actually, wherever the brown rat moves, the black rat is getting replaced, because they are really aggressive toward black rats. The black rats disappear. Its ironic, almost, that people, when they see rats today, they think about the plague and How horrible. But maybe that rat that you see today, like in New York in the subway, is actually the one that saved us from the plague.

Zhang: I think this really speaks to how disease is contingent on human behavior. We might think of diseases as things that just exist in naturetheyre out there and theyre trying to kill us. But whats happening is that these pathogens are only successful if they find and exploit the seams in human behavior. We created the conditions for the plague because we started living in cities, because we started living with rats, because we have fleas.

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Human Teeth Hold the Secrets of Ancient Plagues - The Atlantic