Indeed, Carnival has issued a letter to passengers who've recently traveled on Carnival Glory, which sails seven-night trips out of Port Canaveral, saying that an "an individual tested positive for measles and another individual for rubella (German measles). The two persons were immediately isolated upon suspicion of the illness."
According to Carnival's statement, rubella and measles are rare in the United States as the vast majority of Americans are immune to these illnesses because of the immunization program. Canada also routinely vaccinates children against measles, mumps and rubella (MMR). Speculation that the measles surfaced via crew members is rampant -- indeed, in some cases those staffers do not come from countries where the vaccination is required.
At this point, Carnival is alerting folks from past and future voyages and says it has now screened, vaccinated and counseled.
For more info on measles, go to the Centers for Disease Control web site at www.cdc.gov.