Plagues and other great diseases are important parts of history and some settings. They defy man and may even defy God in their swift and terrible punishment upon the body of society.
My issue with modifying/removing dwarves and elves is that the PC’s may want to play them.
One of the most powerful tools found in the World Building 102b article is the Worksheet. Here is a place to put the settings you might make with them.
The party comes across a nice hermit in the woods. He gives them food and lodging for the night. They awaken to his terrified screams. "East! It's east! Stop it! It'll kill us all!" The poor horror-stricken hermit dies thrashing in agony, one boney arm outstretched, his finger pointing to the east.