Could represent loneliness, cruelty, disloyalty, suffering, bad love..
Illness is a reflection of some emotional/psychological weakness. Not all diseases are equal.
Malaria: bad air signifying malicious gossip, hostile opinion, feverish decisions, overheated state that leads to poor decision making
Grapes of Wrath - Grandpa Joad dies of a stroke. Stroke is a separation of brain and heart. Mind was back at home but body was going to california.
A Christmas Carol - In Scrooge’s vision, Tiny Tim dies from a disease. Causes Scrooge to realize that he needs to help him.