A mystery disease is a disease that has not yet been identified. Reasons for lack of identification of etiology include lack of professional interest, difficult access, and lack of resources, in addition to being unknown to medicine. The following is a list of deadly diseases of which the exact cause is unknown, separated into long-standing and new:
Both "mystery diseases" reported in 2012 for Vietnam and Cambodia have been identified as Ricketsia and Hand, foot and mouth disease, respectively.
Febrile infection-related epilepsy syndrome, a seizure disorder characterized by chronic refractory seizures following an acute refractory seizure phase. It affects children and is preceded by a viral illness such as gastroenteritis or flu.