A fatal degenerative blood disease caused by exposure to the metreon cascade that devastated the Talaxian moon Rinax, which its inventor Ma'Bor Jetrel falsely tells Neelix he has contracted.
Metremia appears in the Voyager episode Jetrel. The Haakonian scientist who designed the metreon cascade comes aboard to warn Neelix that those who went to Rinax after the attack to look for survivors are at risk. The disease breaks down the body at the atomic level and has no cure.
Jetrel examines Neelix and tells him that he has it. The claim is a lie intended to get Voyager to the Talaxian system, where Jetrel hopes to use the transporter to reassemble victims vaporised by his weapon.
Jetrel himself is in the last stage of metremia. His experiment fails, and he dies soon afterwards, though not before Neelix, who has admitted hiding from the war as a deserter, tells him that he forgives him.