Spreading Plague is a rare Druid spell card that belongs to the "Knights of the Frozen Throne" set, which was released on 10.08.2017 and is one of initially 135 cards. The artist of this card was Alexander Alexandrov, who also made 9 other artworks for Hearthstone.
The flavor text of the card is the following: In the past, plagues were spread by mice or fleas. These days they're spread by elves.
The card is easy to memorize with 97.2% of correct quiz questions.