Bubonic plague

The Bubonic Plague was a devastating disease which originated from the Middle Ages, and was spread by rats and fleas, due to the poor cleanliness in that age. it was also noted that the plague was personified by the being known as Death.

A group of escaped Terileptils planned to spread a genetically engineered strain with rats in order to eliminate the human race. The Doctor defeated them, eliminating the storage of viruses in the Great Fire of London, which was unintentionally created whilst fighting the Terileptils. (DW: The Visitation)

Toshiko Sato and Owen Harper have at one time investigated a quarantined hospital which was struck by the plague, which was introduced by a patient who came through the rift from the 14th century. (TW: End of Days)