when people move from one city or country to another, the spread of diseases may result. People often bring in germs that may not have been present there before These new germs can spread quickly and cause previously unknown diseases. If a germ is completely new to a region, people who already live have natural there no protection against it. As a result, they become ill more easily and die more often. In turn, newcomers may catch diseases that were not present where they came from. If they go back, they may carry the disease with them and bring about an epidemic there, too.