|“||Which fatal illness shall I use to kill the great Apolloooo? Anthrax? Perhaps eboooola…||”|
–Nosoi, in The Hidden Oracle
The Nosoi (Singluar "Nosos") are the spirits of illness, plague, and disease. They were one of the many evils locked inside Pandora's Pithos. They are sometimes likened to the Keres. Their Roman equivalent are the Morbi.
On their way to Camp Half-Blood, Apollo, Meg, and Percy were attacked by a group of three Nosoi. One of them manages to infect Apollo. They are weakened by Meg, who used her demigod powers, and later finished off by her friendly Karpos – Peaches.
The Nosoi, in their basic form, were described as vaguely humanoid apparitions. Their bodies are made of glimmering smoke, which renders them invulnerable to any weaponry, even ones made from blessed metals such as Riptide. They can change their form into semi-corporeal; resembling ghoulish corpses with yellow eyes, dressed in destroyed clothes, and covered in festering wounds. Any sort of attack will simply pass through them.
The Nosoi are embodiment of fatal diseases. When they are in their smoke form, they can infect people by making them inhale the vapors of their bodies.
- The Nosoi were responsible for the Black Death in the 14th century.
- Nosoi are often depicted as ravens wearing plagues masks.