Velderix Riehn'va, also known as "The Usurper", was a virulent neurological disease that affected Romulans. The disease progressively weakened artery walls in the brain, resulting in the individual suffering fatal aneurysms if untreated.
In 2381 and 2382, Alizome infected Xarian Dor and Tal'Aura with Velderix Riehn'va, causing the deaths of both. Alizome, who was unaffected by the disease as she was Tzenkethi, had passed the disease onto both by casual contact such as shaking hands.
Dor collapsed at the Hall of State where doctors at the Ki Baratan Medical Center stated that he had seemingly died from Velderix Riehn'va and confirmed that it was an isolated case with no one else being infected by the disease. (ST - Typhon Pact novel: Rough Beasts of Empire)