I'd like to read this book : The Black Death Transformed, by Samuel K Cohn Jnr.
It's reviewed in The Independent

But Cohn does not deviate from his thesis, and as epidemiological detective he is convincing. People developed immunity to Black Death, something medically impossible with bubonic plague. Whatever it was, the new and ferocious disease which first assailed Europe between 1347 and 1352 was not the rat- and flea-borne bacillus with which modern science is familiar.

Having established this revolutionary claim, Cohn does not waste time with speculation as to what the Black Death really was. He is a historian, not a scientist, and he has bigger ideas to explore. Did the speed and confidence with which rational investigation and treatment of plague replaced pessimistic religiosity lay the foundations for the Renaissance?