Arctic of Canada. In addition, measles and other “crowd diseases” tend to kill infected adults rather than children, yet all adults in that tribe are infected. By contrast, modern Americans rarely catch measles if they are adults because most or have had measles or were vaccinated against measles as a child. After killing most people in the tribe, the epidemic disappeared. Cats She Lived Happily Ever After poster. The meager population of the tribes is not only the reason why their populations are unable to sustain the epidemic from outside for a long time, but also why they never being able to create its own contagious diseases to infect those who came from far away.