A spaceborne virus is a type of highly virulent pathogen.
The Brunali employed genetic engineering to create children that produced a spaceborne virus deadly to the Borg and other cybernetic organisms. They then allowed these children to be assimilated, spreading the pathogen to their Borg vessels.
In 2376, Icheb, one such child, was assimilated by a Borg cube. He spread the virus to the drones on board, killing the entire crew save for the neonatal drones, who were protected by their maturation chambers. Icheb and four others were subsequently awakened, and encountered the USS Voyager. The Voyager crew investigated the use of the virus as a biological weapon, though it was never deployed. (VOY: "Collective", "Child's Play")