Colder weather, failed harvests, and resulting malnourishment left Europe’s population susceptible to disease, and unfortunately for the continent, a virulent one appeared in the mid-fourteenth century. Around 1300 improvements in ship design had allowed year-round shipping for the first time. European merchants took advantage of these advances, and ships continually at sea carried all types of cargo. They also carried vermin of all types, especially insects and rats, both of which often harbored pathogens. Rats, fleas, and cockroaches could live for months on the cargo carried along the coasts, disembarking at ports with the grain, cloth, or other merchandise. Just as modern air travel has allowed diseases such as AIDS and the H1N1 virus to spread quickly over very long distances, medieval shipping allowed the diseases of the time to do the same. The most frightful of these diseases, carried on Genoese ships, first emerged in western Europe in 1347; the disease was later called the Black Death.