bruise-like purple
blotches, called buboes, on the victim's skin. It is from this
word, buboe, that the bubonic plague takes its name. The
hemorrhaging causes an intoxication of the nervous system, which
produces neurological and psychological disorders, including
insomnia, delirium, and stupor
Septicaemic plague is, like the bubonic plague, carried by
insects. Its distinguishing feature is its rapidity - death occurs
within a day of infection, even before buboes have had time to
form. This form of the plague is the rarest rare, but is almost
always fatal
victims suffer a sharp drop in body temperature,
which is followed by sever coughing and discharge of a bloody
sputum
airborne transmission.
None of these plagues are native to Europe.
bacteria
normally resides in Central Asia, Yunan China, Arabia, East Africa,
and limited areas of Iran and Libya.
Their spread to Europe from these areas has always been
through global commerce - trade which carried with it plague-
bearing rats and fleas.
From China, the plague is known to have been carried along the
Silk Road into Central Asia, where there are records of outbreaks
in 1339.
If we're right, we'll have to rewrite that part of history."
The Black Death, which originated in Asia, arrived in Europe in 1347 and caused one of the deadliest outbreaks in human history.
It had been thought that black rats were responsible for allowing the plague to establish in Europe, with new outbreaks occurring when fleas jumped from infected rodents to humans.
They compared tree-ring records from Europe with 7,711 historical plague outbreaks to see if the weather conditions would have been optimum for a rat-driven outbreak.
"We show that wherever there were good conditions for gerbils and fleas in central Asia, some years later the bacteria shows up in harbour cities in Europe and then spreads across the continent," Prof Stenseth said.
He said that a wet spring followed by a warm summer would cause gerbil numbers to boom.
And because this was a period when trade between the East and West was at a peak, the plague was most likely brought to Europe along the silk road, Prof Stenseth explained.
"Suddenly we could sort out a problem. Why did we have these waves of plagues in Europe?
The team now plans to analyse plague bacteria DNA taken from ancient skeletons across Europe.
If the genetic material shows a large amount of variation, it would suggest the team's theory is correct.