[blam]

"More than likely the resistance developed during a period when a Founder Population lived in a rodent infested region ~ probably the Arctic ~ they would have made their way South over thousands of years, gradually blending into the local population."

This article is a condensed version from the one in Archaeology Magazine. In the magazine version, it has this to say:

Most researchers now believe that the Black Death was the bubonic plague. Caused by the bacterium Yessinia pestis, it spread from rats to humans, usually by means of an infected flea.
But historical records show that the Black Death occurred in areas such as Iceland, where there were no rats. As a result, historian Susan Scott and Liverpool zoologist Chris Duncan suggest that Black Death was a viral hemorrhagic fever, akin to the Ebola Virus.
No one, however ,debates its lethal effect. In just three years, the Black Death swept across Europe, as far north as the Arctic Circle, claiming the lives of 40 percent of its inhabitants. And over the next three centuries, it struck repeatedly on the continent, filling graveyards whenever it appeared."

[muawiyah]

Blam, Barbara Tuchman reported that the virulence of the Black Death declined as it moved North, and by the time it got to the Arctic the death rate was less than 10%.

Guess who lives in the Arctic where the only animals other than wolves, bear and reindeer are rodents. Well, I guess you don't need to guess eh!.