Quote:
Bubonic and septicaemic plague are transmitted by direct contact with fleas, most notably the rat flea Xenopsylla cheopsis. The bacteria multiply inside a flea, blocking its stomach and causing it to become very hungry. The flea then voraciously bites a host and continues to feed because it is unable to satisfy its hunger. During the feeding process, infected blood carrying the plague bacteria flows from the fleas' stomachs into the open wound. The plague bacteria then has a new host, and the flea eventually dies from starvation.
The human pneumonic plague has a different form of transmission. It is transmitted through bacteria in droplets of saliva coughed up by persons with bloodstream infection (sepsis) or pneumonia, which may have started as the bubonic form of disease. The airborne bacteria may be inhaled by a nearby susceptible person, and a new infection starts directly in the lungs or throat of the other, bypassing the bubonic form of disease.
It doesn't say rats necessarily, but the fleas. It's very possible even in areas where "rats" weren't seen, that someone could have been bitten during travel of some sort or could have come into contact with someone who had it, then brought it back home to Iceland.