Dear Secretagent,
Sorry, my typo. Due to my old age, I accidentally typed Eruvin when I meant Ta’anis, which is the mesechta we are discussing. So again, see tosfos Ta’anis 21:, d”h Amru, where according to the historians, tosfos seems to be referring to the Black Plague.
This discovery is not a shock. Ohrbach quotes the Maharshal (Shu”t Maharshal 64) at the beginning of his discussion that tosfos on Ta’anis is “?? ?????????”