When Jake Rosmarin boarded the MV Hondius, he gleefully posted on social media that the ship would be his home for 35 days as he traveled across the South Atlantic .

Now, he is one of 18 Americans under observation at specialized health care facilities designed to treat people with dangerous infectious diseases after three people died and others were sickened by a hantavirus outbreak aboard the ship.

Rosmarin, 30, said he expects to spend 42 days at the National Quarantine Unit at the University of Nebraska Medical Center in Omaha .

Fourteen other American passengers from the ship are also there. Another who tested positive for the virus is in the Nebraska Biocontainment Unit.…