[BRIEF NOTE] Two thoughts on the huge petty details of the Black Death

[rfmcdonald]

The news that the bacterium Yersinia pestis has been identified as the cause of the Black Death of the 14th century impresses me for two reasons. The first is the subtlety of the study.

The researchers studied DNA from the remains of 109 skeletons, now more than 650 years old, that were buried in the East Smithfield grave outside London’s old walls during the plague.

Poinar and his team took bone and teeth samples to get a hold of whatever small bits of DNA they could find. They then used a unique technique to look for Yersinia pestis among the morass of viruses, bacteria and human genes.

The researchers launched a protein-laced fishing line into this genetic pool designed to attract Yersinia pestis. Once the bacterium attached itself to the fishing line, the researchers used magnets to separate it out so they could map its genetic makeup.

Poinar said his team was only able to pull a small amount of the bacterium’s genetic markers. In all, the genetic string reaches more than 4.6 million units and Poinar’s team was able to capture about 50 to 60 units.

The second is the apparently very minor change it took for Yersinia pestis to become a mass killer.

The differences between Yersinia pestis and its soil-based cousin are small, said Hendrik Poinar, one of the lead authors on the study from McMaster University in Hamilton.

The task now is to determine how a harmless microbe turned into a deadly killer and better prepare for a future pandemic, Poinar said.

“The question is, can we identify what made the pathogen so bad?”said Poinar, an evolutionary geneticist at McMaster’s Michael G. DeGroote Institute for Infectious Disease Research.

“That’s the million-dollar question and we don’t have an answer yet, but that’s what we’re targeting.”

The study also suggests that the Black Plague was one of three pandemics beginning with the Plague of Justinian in 541 AD and culminating with the modern bubonic plague that is driven by international travel and trade.

Yersinia pestis is responsible worldwide for the deaths of approximately 2,000 people annually from the bubonic plague, but it is not nearly as powerful as the Black Death. Poinar said that no outbreak has been as deadly as Black Death.

“We’ve been relatively disease free,” Poinar says. “We’ve had infections such as HIV/AIDS that have killed millions of people, but not to the same extent.”

Details matter. Clearly.