The quote seems to be a paraphrase coming from Nietzche's Zur Genealogie der Moral:
But thereby he introduced that most grave and sinister illness, from which mankind has not yet recovered, the suffering of man from the disease called man
This was published in 1887.
Mit ihm aber war die grösste und unheimlichste Erkrankung eingeleitet, von welcher die Menschheit bis heute nicht genesen ist, das Leiden des Menschen am Menschen, an sich
which google translates a bit differently (probably more politically correctly):
But with him the biggest and scariest disease was initiated, of which humanity is still not recuperated, the suffering of the people on the people, per se.
According to Google N-Gram viewer, the above is the earliest usage of the idiom "disease called man".
Otherwise, you found another great source on our Philosophy site, where you also cite another book of his Also sprach Zarathustra:
in Thus Spake Zarathustra (section 40, "Great Events"), in the discourse with the fire-dog, Nietzsche has Zarathustra say the following:
Die Erde, sagte er, hat eine Haut; und diese Haut hat Krankheiten. Eine dieser Krankheiten heisst zum Beispiel: "Mensch." [The earth, said he, hath a skin; and this skin hath diseases. One of these diseases, for example, is called "man."]
This book was published earlier still, 1883, but uses a slightly different version of the idiom "disease called man".