Twin Fever is mentioned in a scan in Metroid Prime as a viral-based disease native to Twin Tabula in the FS-176 System. The early symptom, and the source of its name, is double vision, known as 'twin sight'. When this symptom vanishes, it indicates that death is near. It is either unknown or has not yet been revealed if the disease is contagious, though it most likely is since it is virus-based, though how it passes from being to being is not revealed. The planet was quarantined due to this deadly disease.