when people move form 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 there have no natural 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.