Currently, the plague still infects several thousand people every year around the world, though most patients recover if treated early enough with antibiotics. When they compared the strain of plague preserved in this medieval DNA with the strain that recently killed some 60 people in Madagascar, however, they found something surprising. The medieval strain was no stronger than the recent one; in fact, their genetic codes matched almost exactly.
Scientists at Public Health England in Porton Down, argue that for the Black Death to have spread so quickly and killed so many victims with such devastating speed, it would have to have been airborne. Therefore, rather than bubonic plague, which is transmitted to humans through bites from infected rat fleas, they concluded that this must have been a pneumatic plague that made its way into the lungs of the infected and spread through coughs and sneezes.