Infectious diseases that occur in humans in the form of a pandemic, rather than at regular intervals, have some common characteristics. First of all, they spread rapidly and effectively from an infected person to surrounding healthy people, resulting in the whole population being infected in a short time. Dog And She Lived Happily Ever After poster. Second, they are “acute” diseases, that is, in a short time, the patient either dies or fully heals. Thirdly, those who are fortunate among us to recover will have antibodies that will help immunity to that disease for a long time, possibly for the rest of our lives.