Nanospore

Nanospores were an insidious Grigari weapon that was deployed against the Federation in the alternate future known as the War of the Prophets created when the Red Orbs of Jalbador created the Red Wormhole.

Nanospores are nanites that infiltrate biological cells where they destroy the body from the inside out and use whatever materials they have access to within the living organisms body to create more of themselves. Nanospores could not be blocked by biofilters and resulted in many worlds being uninhabitable. Starfleet was forced to impose a qurantinee on those worlds affected to prevent the spread of the nanospore plague.

(DS9 novel: Millennium The War of the Prophets'')