Yep, an unusually wet year causes an explosion in the rodent population and those are the years the plague pops up. It has been that way long enough that the Navajo and Hopi both have stories about it passed down from the elders for many generations in Northern AZ, and NM.
I always heard the fleas on rodents and even rabbits carried it, my dad told us not to eat rabbits though some people did after a hard freeze.
Yes, the fleas transmit the disease from the rodents to people.