Metremia was a fatal degenerative blood disease associated with exposure to the unique metreon isotopes released by the metreon cascade weapon.
Attacking its victims on the molecular level, it caused the body's atomic structure to undergo fission, a slower reaction similar to the way the Metreon Cascade vaporized its victims through bio-molecular disintegration.
It apparently had similar effects on Haakonian and Talaxian physiology. It might lay dormant for years, and sufferers could apparently keep on operating as normal for some time after the disease was diagnosed; Doctor Ma'Bor Jetrel was one victim of the disease who nevertheless managed to continue his work and research without any sign of suffering until the last few days of his life left him too weak to keep going. (VOY: "Jetrel")