A vacationing doctor who stepped in to treat hantavirus patients on the MV Hondius after the ship’s chief medic fell ill is isolating inside a biocontainment unit after also contracting the virus.  Retired oncologist Stephen Kornfeld was put in isolation after landing in Omaha, Nebraska – but told CNN Tuesday he’s feeling wonderful and currently showing no symptoms. Kornfeld, one of 18 passengers who arrived in Omaha Monday, said he experienced flu-like symptoms while at sea — unaware that it could be hantavirus.   Stephen Kornfeld, a doctor who was vacationing on the MV Hondius, tested positive for the virus. Dr.…