Anyone who was at Caffa (traders, villagers, siegers) were infected and they carried the disease into Europe.
In the fourteenth century most of Europe, southern and eastern Asia and Nothern Africa had settled in permanent villages and towns
Soon these settlemnets realised how beneficial peaceful trade was. Networks and roads devoloped throughout Europe and soon trade was happening nearly everywhere, and Europeans were regularly going into Asia and other places they wouldn't usually go.
Written reports say that outbreaks of the Black Death may have occurred in China in 1320s and 1330s. It was brought their by the Mongols who ruled there who brought the disease from Central Asia to China. The central of China is considered to be the first major outbreak.
Trade between China and Europe was increasing, using the Silk Road. The potential was always there for the Black Death to be carried to Europe from traders or from Mongolian Warriors.
Caffa was a big part in spreading the plague. Caffa was a major shipping port for trade in the black sea. In 1347 Tartars attacked the city.
As they sieged the city Tartars bean falling sick to a disease and large numbers of them died quickly. The Tartars withdrew but before they did they catapulted the dead into the city.
Caffa was in Italy. 1348 the plague was in nothern Italy, and from there spread to the rest of Italy, France and spain by the middle of the year.
Within a year all western Europe was affected and in 1350 the black death turned east again and reached russia. The middle east was also a victim
The Plague also reached north africa, but did not spread throughtout africa since the cities it afflicted were surronded by tribal settlements and black rats prefer living in places like England.