Answer: People who came from Messina
Explanation: The arrival of the plague in western Europe happened in October 1347, when Genoese vessels en route from the Crimea region moored at Messina. The disease, caused by the bacterium Yersinia pestis, was transmitted with fleas (Xenopsylla cheopis) infesting black rats (but also certain other animals). Humans were usually infected when bitten by these fleas. Bubonic plague is fatal (though there is now a cure) and leads to an infection of the lymph nodes, which become swollen (bubo is Latin for "bump").
Here's what actually happens. The bacteria grow inside the flea, causing conditions which block the insect's stomach and induce extreme hunger. The flea starts to feed on a host, and in this way the disease spreads.