It's beginnings in Europe were not exactly subtle. It arrived in Sicily via a ship whose crew were all dead or infected. It was likely noticed before its first victim set foot on European soil. There are similar stories of it arriving via infected vessels to other European cities, particularly in England.

If you look up the symptoms, it was pretty hard to miss and pretty hard to ignore its severity. It also spread and killed very quickly. Something like 4 miles a day over land with a life expectancy in the neighborhood of 3 days once contracted.