In his exposition to the short story, "The Masque of the Red Death," Edgar Allan Poe's narrator describes the "Red Death" as having long devastated the country; in fact, no pestilence had ever
been so fatal, or so hideous. Blood was its Avatar and its seal--the redness and the horror of blood.
While the Prince and his light-hearted friends, knights and dames of his court seek refuge in the abbey, the Red Death, nevertheless, finds them. Prince Prospero demands that this intruder be seized and unmasked. But, the Red Death passes through the blue chamber to the purple, then the green, then the orage and white to the violet. Enraged Prince Prospero runs through the chambers, brandishing a dagger, but to no avail. Like "a thief in the night," the Red Death comes, staining the "blood-bedewed hall of their revel," and each guest dies in the "despairing posture of his fall." The life of the ebony clock goes out.
And the flames of the tripods expired. And Darkness and decay and the red Death held illimitable dominion over all.
To pull from Poe himself there are these vivid words: "hideous," "a deadly terror," "blood-bedewed halls," "Darkness" and "Decay" with "illimitable dominion."
For the disease itself, it would be: enigmatic, horrific, vomitive, disgusting, deadly
For the guest: terrifying, unexpected, machiavelic, diabolical, sadistic
-hope that works!