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 of Center...