General:
* Epidemic: A widespread occurrence of an infectious disease in a community at a particular time.
* Outbreak: A sudden increase in the number of cases of a disease.
* Scourge: A cause of great suffering or destruction.
* Blight: A disease that affects plants, or something that causes widespread destruction.
More specific:
* Pestilence: A deadly or infectious epidemic disease.
* Contagion: The communication of a disease by contact.
* Infection: The invasion of the body by a pathogenic organism.
* Infestation: The presence of an excessive number of organisms, typically parasites or insects.
* Pandemic: An epidemic that spreads over a wide geographic area, often worldwide.
Figurative:
* Torment: Severe suffering or distress.
* Curse: A cause of great misfortune or suffering.
* Affliction: A condition that causes great suffering.
The best word to use will depend on the specific context of your writing.