The virus is usually spread from rodents, but the WHO said in this instance it could have spread among "really close contacts" aboard the MV Hondius vessel. It stressed the risk to the public was low. Two crew members - one British and one Dutch - are due to be medically evacuated by aircraft to the Netherlands after displaying "acute respiratory symptoms", the ship's operator Oceanwide Expeditions said. MV Hondius set sail from Argentina on its voyage across the Atlantic Ocean around a month ago. It is currently anchored near Cape Verde, off Africa's west coast. Medical teams from Cape Verde, supported by the WHO, have boarded the ship to help with the suspected cases, spokesperson Tarik Yasarevic told the BBC. Testing is taking place for other passengers and crew members who are displaying symptoms. Images taken from on board the cruise ship show workers in hazmat suits in a smaller vessel alongside. Some 149 people from 23 countries remain aboard under "strict precautionary measures", Oceanwide said. They include around 20 British nationals, according to a UK government spokesperson. "We do believe that there may be some human-to-human transmission that is happening among the really close contacts", WHO official Dr Maria Van Kerkhove said. She added that the WHO suspected the first person to fall ill could have contracted the virus before boarding the ship. Seven cases of hantavirus - two confirmed and five suspected - have so far been identified, according to the latest WHO update. (BBC)