evil is not something that exists outside of human kind and the jinn, as everything else is in submission to Allah - evil occurs when human kind or jinns go against their nature and knowingly disobey Allah, anything that occurs through this knowing disobeying is evil, even if it appears to be pleasant or beneficial to the doer. natural diseases, catastrophes etc are not evil as they happen by the will of Allah - they are just unpleasant to personally experience, but not evil. indeed Allah works in ways beyond what we can keep track of. - we may hate a thing that is good for us or love a thing which is bad for us. sometimes He may protect us with something that we find unpleasant, from something far far worse. to understand this read the story of Khidr (raa) and Musa (as) in the Holy Qur'an.