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The Mutant Genes Behind the Black Death
An anonymous reader writes: Each year, 4 million people visit Yosemite National Park in California. Most bring back photos, postcards and an occasional sunburn. But two unlucky visitors this summer got a very different souvenir. They got the plague. This quintessential medieval disease, caused by the bacterium Yersinia pestis and transmitted most often by fleabites, still surfaces in a handful of cases each year in the western United States, according to the Centers for Disease Control and Prevention. Its historical record is far more macabre. The plague of Justinian from 541 to 543 decimated nearly half the population in the Mediterranean, while the Black Death of the Middle Ages killed one in every three Europeans.
Now researchers are beginning to reveal a surprising genetic history of the plague. A rash of discoveries show how just a small handful of genetic changes — an altered protein here, a mutated gene there — can transform a relatively innocuous stomach bug into a pandemic capable of killing off a large fraction of a continent.
The most recent of these studies, published in June, found that the acquisition of a single gene named pla gave Y. pestis the ability to cause pneumonia, causing a form of plague so lethal that it kills essentially all of those infected who don't receive antibiotics. In addition, it is also among the most infectious bacteria known. "Yersinia pestis is a pretty kick-ass pathogen," said Paul Keim, a microbiologist at Northern Arizona University in Flagstaff. "A single bacterium can cause disease in mice. It's hard to get much more virulent than that."
Now researchers are beginning to reveal a surprising genetic history of the plague. A rash of discoveries show how just a small handful of genetic changes — an altered protein here, a mutated gene there — can transform a relatively innocuous stomach bug into a pandemic capable of killing off a large fraction of a continent.
The most recent of these studies, published in June, found that the acquisition of a single gene named pla gave Y. pestis the ability to cause pneumonia, causing a form of plague so lethal that it kills essentially all of those infected who don't receive antibiotics. In addition, it is also among the most infectious bacteria known. "Yersinia pestis is a pretty kick-ass pathogen," said Paul Keim, a microbiologist at Northern Arizona University in Flagstaff. "A single bacterium can cause disease in mice. It's hard to get much more virulent than that."
In each iteration these pathogens got more and more lethal....This explanation came out as a 12 page (The arrow of disease) article by Jared Diamond in 1992 in the Discover magazine. Later it was expanded into a Pulitzer winning book, Guns, Germs and Steel
IIRC, Jared's argument in GG&S was that each iteration became less and less lethal. No only did the humans with better natural protections survive and have offspring, but the disease itself survived better if it didn't kill off all its hosts, so it had evolutionary pressure to be less deadly and more endemic.