Sakuro's disease was a medical condition. It was first named after a man named Sakuro. Symptoms included fever and weakness. In the 23rd century, the disease was a serious condition, but could be cured in a hospital or starship sickbay provided it was diagnosed early after infection.
Among those who succumbed to this disease are Nancy Hedford and Demora Sulu's mother, Susan Ling. (TOS episode & novelization: Metamorphosis; TOS novel: The Captain's Daughter, ST - The Lost Era novels: Serpents Among the Ruins, One Constant Star)