The singer announced the end of the tour, including his scheduled June 21 date with Sir Cliff Richard in New York, with "unimaginable sorrow".
A message posted on True To You, a popular Morrissey fan site used for his official announcements, said he collapsed after his show in Boston on Saturday.
It said he fell ill after catching "a horrendous cold" from his support act Kristeen Young in Miami, adding: "Morrissey received medical attention in Miami, and once again in Boston, but it was not enough to shake off the virus, the recovery time for which is too lengthy to meet the final 9 shows of the tour."
When the date with Sir Cliff was initially announced, the Devil Woman singer admitted he could not name any of the ex-Smiths singer's hits.
He said: "I couldn't tell you the titles. I've just googled him to see what kinds of crowds he plays to and what sort of show he did. I'm thinking, okay, it looks like a pop-rock show."
It is not the first time ill-health has forced Morrissey from the stage. Last year he cancelled a string of US dates after suffering a bleeding ulcer, Barrett's oesophagus and double pneumonia.