Macro-virus

Life cycle
The Macro-viruses reproduced by infecting individuals of other species. These individuals would seemingly develop a disease which in humans resembled the Black Death, until at a later stage they would rapidly transform into another Macro-virus. (IDW: Black Death White Life)

History
The Macro-viruses waged a constant war on the flesh planet Mimosa 3, which was defended by Immnoglobulins. Following one battle their enemies were decimated, and one of the Immunoglobulin generals fled the planet. and a trio of Macro-viruses followed to destroy it, eventually arriving on Earth.

Disguised as plague doctors, they managed to find it in 1669 in a rural English village. In the meantime they sought to recruit more individuals into their army, infecting Martha Jones among others. They attacked the church it stayed in but were destroyed when it regained its full powers and divided into a new army. (IDW: Black Death White Life)