[gleeaikin]

The disease may have started with gerbils, but it spread to rats, and the rats aboard ships almost certainly carried the infected fleas west to Europe. Another problem is that the vector in Europe was most likely the black rat which lives in the upper part of houses and buildings. The gray Norway rat is a cellar and sewer dweller and probably not as big a danger to people should it be infected by fleas.

[SunkenCiv]

The rat difference isn’t the where they live so much as their lifestyle — one is nocturnal, the other one (the one seen walking along the sidewalks in large NE cities in the US) isn’t. :’)

[SunkenCiv]

Thanks gleeaikin.