Throughout the play Hamlet, Shakespear displays many underlying themes by way of imagery. A quick summary of the play would go as follows: Hamlet returns home from school after learning that his father is dead. When he arrives, he discovers his uncle Claudius is married to his mother Gertrude and is now king. Thing begin turning sour around him when his best friend Horatio and a couple guards show him a ghost who looks like his father. The ghost delivers a message to Hamlet, one that involves revenge by killing Claudius. Hamlet can't decide what to do, and many things have fallen apart because of the poisoning act on the part of Claudius. At this time Hamlet starts acting mad, likely as a result of the tumultuous events occurring around him. While Hamlet is mad, he kills his love interest Ophelia's father, Polonius. The death of her father causes Ophelia to commit suicide (or so it seems). At the end of it all, Hamlet duels a rival of his, and ends up dying along with most all of the other characters in the story. Throughout the story, disease plagues Denmark and the people in it, shown by imagery that Shakespear delivers consistently throughout.
In the opening scene, Horatio makes an interesting statement: "As stars with trains of fire and dews of blood, Disasters in the sun; and the moist star upon whose influence Neptune's empire stands was sick almost to doomsday with eclipse (1.1.117-120)." He compared the ghost as a possible sign of disaster or catastrophe in Denmark, as to what happened before the death of Julius Caesar. From the start of the play, Denmark was already tainted and wrought with disease that would eventually continue over the course of the play.
In Hamlet's first soliloquy, he states that the world is "an unweeded garden,.
That grows to seed; things rank and gross in nature possess it merely (1.2.135-137)." Like a spreading weed in a garden, the world is being spread with disease, all starting with the incestuous marriage of Gertrude and Claudius.