Moan'na

 was a Hakuai who had to run away from his own people. He hid himself in England in the 17th century, and disguised himself as a human with a biological resequencer. In 1665, Moan'na got the bubonic plague and died from it. Buried in a plague pit, the resequencer continued to change and evolve the plague in his body. When the Victoria line extension was built in the late 20th century, the vibrations awoke Moan'na's infected corpse, reanimated by the biological resequencer, and he infected Lloyd Collins. The Twelfth Doctor short-circuited the wiring that animated Moan'na's cadaver by electrifying the train tracks. (COMIC: The Pestilent Heart)