Yes, of course fleas can transmit lyme bacteria. I always said that ticks get too much credit!
The "host" of most lyme bacteria is the White Footed Mouse, yeah, they are the real culprit. They live most everywhere, in the U.S., Canada, Europe, etc. Any blood sucking bug that feeds on these mice will then carry lyme bacteria. I believe I read that the first identified rodent that carried lyme bacteria was found in 1890 in Germany.. I think lyme has been around forever but no one knew what it was or what to call it.