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 healthcare facilities designed to treat people with dangerous infectious diseases after three people died and others were sickened by a hantavirus outbreak onboard 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.…