At least 75 million people—including more than half of Britain’s population—are believed to have died during the 14th and 15th centuries from the plague known as the Black Death. For years, the fatal disease's spread was widely blamed on infected rats' fleas. But now, thanks to a trove of 25 skeletons unearthed by work on a new London railway line last year, scientists now believe the disease was instead likely airborne. How was this historic information gleaned? Teeth pulled from the centuries-old skeletons.
The Guardian with the details of the toothy discovery (emphasis mine):
By extracting the DNA of the disease bacterium, Yersinia pestis, from the largest teeth in some of the skulls retrieved from the square, the scientists were able to compare the strain of bubonic plague preserved there with that which was recently responsible for killing 60 people in Madagascar. To their surprise, the 14th-century strain, the cause of the most lethal catastrophe in recorded history, was no more virulent than today's disease. The DNA codes were an almost perfect match.
According to scientists working at Public Health England in Porton Down, for any plague to spread at such a pace it must have got into the lungs of victims who were malnourished and then been spread by coughs and sneezes. It was therefore a pneumonic plague rather than a bubonic plague. Infection was spread human to human, rather than by rat fleas that bit a sick person and then bit another victim. "As an explanation [rat fleas] for the Black Death in its own right, it simply isn't good enough. It cannot spread fast enough from one household to the next to cause the huge number of cases that we saw during the Black Death epidemics," said Dr Tim Brooks from Porton Down.
The skeletons were excavated after they were found by construction crews working on the Crosstrail Line in London's Charterhouse Square. Teams of archaeologists, scientists, historians and physicists are continuing to examine the remains for more information about both the plague and life during those centuries, according to the Associated Press. More more on the discovery here and here.