Deadly Black Death bug hasn’t changed, but we have

SETH BORENSTEIN

AP Sci­ence Writer

WASHINGTON — Sci­en­tists have cracked the genetic code of the Black Death, one of history’s worst plagues, and found that its mod­ern day bac­te­r­ial descen­dants haven’t changed much over 600 years.

Luck­ily, we have.

The evo­lu­tion of soci­ety and med­i­cine — and our own bod­ies — has far out­paced the evo­lu­tion of that deadly bac­terium, sci­en­tists said.

The 14th cen­tury bug Yersinia pestis is nearly iden­ti­cal to the mod­ern day ver­sion of the same germ. There are only a few dozen changes among the more than 4 mil­lion build­ing blocks of DNA, accord­ing to a study pub­lished online Wednes­day in the jour­nal Nature.

What that shows is that the Black Death, or plague, was deadly for rea­sons beyond its DNA, study authors said. It had to do with the cir­cum­stances of the world back then.

In its day, the dis­ease killed between 30 mil­lion and 50 mil­lion peo­ple — about 1 of every 3 Euro­peans. It came at the worst pos­si­ble time — when the cli­mate was sud­denly get­ting colder, the world was in the midst of a long war and hor­ri­ble famine, and peo­ple were mov­ing into closer quar­ters where the dis­ease could infect them and spread eas­ily, sci­en­tists say. And it was likely the first time this par­tic­u­lar dis­ease had struck humans, attack­ing peo­ple with­out any innate protection.

“It was lit­er­ally like the four horse­man of the apoc­a­lypse that rained on Europe,” said study lead author Johannes Krause of the Uni­ver­sity of Tub­in­gen in Ger­many. “Peo­ple lit­er­ally thought it was the end of the world.”

In dev­as­tat­ing the pop­u­la­tion, it changed the human immune sys­tem, basi­cally wip­ing out peo­ple who couldn’t deal with the dis­ease and leav­ing the stronger to sur­vive, said study co-author Hen­drik Poinar of McMas­ter Uni­ver­sity in Ontario.

But sim­ple antibi­otics today, such as tetra­cy­cline, can beat the plague bac­te­ria, which doesn’t seem to have prop­er­ties that enable other germs to become drug resis­tant, Poinar said. Plus, changes in med­ical treat­ment of the sick, cou­pled with improved san­i­ta­tion and eco­nom­ics, put human­ity in a far bet­ter posi­tion. And there’s an immune sys­tem pro­tec­tion we mostly have now, Poinar said.

“I think we’re in a good state,” Poinar said. “The rea­son we do so well is that con­di­tions are so different.”

Peo­ple still get the dis­ease, usu­ally from fleas from rodents or other ani­mals, but not that often. There are around 2,000 cases a year in the world, mostly in rural areas, with a hand­ful of them pop­ping up in remote parts of the United States, accord­ing to the Cen­ters for Dis­ease Con­trol and Pre­ven­tion. Ear­lier this year, two peo­ple in New Mex­ico were diag­nosed with plague. In 1992, a Col­orado vet­eri­nar­ian died from a more recent strain, one that sci­en­tists used heav­ily in their study.

To get the orig­i­nal Black Death DNA, sci­en­tists played den­tist to dozens of skeletons.

Dur­ing the epi­demic in the 14th cen­tury, about 2,500 Lon­don area vic­tims of the dis­ease were buried in a spe­cial ceme­tery near the Tower of Lon­don. It was exca­vated in the mid-1980s with 600 indi­vid­ual skele­tons moved to the Museum of Lon­don, said study co-author Kirsten Bos, also of McMas­ter Uni­ver­sity. She then removed 40 of those teeth, drilled into the pulp inside the teeth and got “this dark black pow­dery type mate­r­ial” which likely was dried blood that included DNA from the bacteria.

And when she was done, Bos returned the teeth, minus a lit­tle DNA, to the skele­tons at the museum.

When the same sci­en­tists first tried map­ping the bacteria’s genetic makeup, it appeared to be a dis­tinctly dif­fer­ent germ than what is around cur­rently. But part of that was a reflec­tion of work­ing with 660-year-old DNA and newer, more refined tech­niques revealed less dif­fer­ence between the early day and mod­ern Y. pestis bac­te­ria than between a mother and daugh­ter, Krause said.

That’s a sur­pris­ing result, but the work was well done and makes sense, said Julian Parkhill, a dis­ease genome expert at the Well­come Trust Sanger Insti­tute in Britain. Parkhill was not involved in the research but has stud­ied the bacteria.

“Get­ting an effec­tively com­plete genome sequence of a bac­terium that lived nearly 700 years ago is incred­i­bly excit­ing,” Parkhill said.

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