Anthrax

Anthrax was a disease which Sam thought he'd contracted from letters he'd been reading when the First Doctor told him the building was under quarantine. The Doctor assured him, though, that it was not anthrax he'd been infected with. It was a meme. (PROSE: INtRUsioNs)

When Ferran read the Eighth Doctor's memories, he saw anthrax — along with multiple wars, rape, flooding mines, AIDS, stock market crashes, concentration camps and Agent Orange — as an example of evil on Earth. (PROSE: Father Time)